diff --git a/.travis.yml b/.travis.yml
index 6775e6021..225421756 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,7 +17,7 @@ matrix:
         - pip freeze
       script:
         - mypy openslides/ tests/
-        - pytest --cov --cov-fail-under=76
+        - pytest --cov --cov-fail-under=75
 
     - language: python
       name: "Server: Tests Python 3.7"
@@ -36,7 +36,7 @@ matrix:
         - isort --check-only --diff --recursive openslides tests
         - black --check --diff --target-version py36 openslides tests
         - mypy openslides/ tests/
-        - pytest --cov --cov-fail-under=76
+        - pytest --cov --cov-fail-under=75
 
     - language: python
       name: "Server: Tests Startup Routine Python 3.7"
diff --git a/client/package.json b/client/package.json
index 81a104ac2..65ef9b540 100644
--- a/client/package.json
+++ b/client/package.json
@@ -24,8 +24,8 @@
         "po2json-tempfix": "./node_modules/.bin/po2json -f mf src/assets/i18n/de.po /dev/stdout | sed -f sed_replacements > src/assets/i18n/de.json && ./node_modules/.bin/po2json -f mf src/assets/i18n/cs.po /dev/stdout | sed -f sed_replacements > src/assets/i18n/cs.json",
         "prettify-check": "prettier --config ./.prettierrc --list-different \"src/{app,environments}/**/*{.ts,.js,.json,.css,.scss}\"",
         "prettify-write": "prettier --config ./.prettierrc --write \"src/{app,environments}/**/*{.ts,.js,.json,.css,.scss}\"",
-        "cleanup": "npm run lint-write; npm run prettify-write",
-        "cleanup-win": "npm run lint-write & npm run prettify-write"
+        "cleanup": "npm run prettify-write; npm run lint-write",
+        "cleanup-win": "npm run prettify-write & npm run lint-write"
     },
     "dependencies": {
         "@angular/animations": "^8.0.3",
diff --git a/client/src/app/core/core-services/autoupdate.service.ts b/client/src/app/core/core-services/autoupdate.service.ts
index 2ff1b4908..d12a5b235 100644
--- a/client/src/app/core/core-services/autoupdate.service.ts
+++ b/client/src/app/core/core-services/autoupdate.service.ts
@@ -96,7 +96,10 @@ export class AutoupdateService {
         Object.keys(autoupdate.changed).forEach(collection => {
             elements = elements.concat(this.mapObjectsToBaseModels(collection, autoupdate.changed[collection]));
         });
+
+        const updateSlot = await this.DSUpdateManager.getNewUpdateSlot(this.DS);
         await this.DS.set(elements, autoupdate.to_change_id);
+        this.DSUpdateManager.commit(updateSlot);
     }
 
     /**
@@ -107,7 +110,7 @@ export class AutoupdateService {
         const maxChangeId = this.DS.maxChangeId;
 
         if (autoupdate.from_change_id <= maxChangeId && autoupdate.to_change_id <= maxChangeId) {
-            console.log('ignore');
+            console.log(`Ignore. Clients change id: ${maxChangeId}`);
             return; // Ignore autoupdates, that lay full behind our changeid.
         }
 
diff --git a/client/src/app/core/core-services/constants.service.ts b/client/src/app/core/core-services/constants.service.ts
index 58de7dd1f..00b90d4d0 100644
--- a/client/src/app/core/core-services/constants.service.ts
+++ b/client/src/app/core/core-services/constants.service.ts
@@ -1,6 +1,7 @@
 import { Injectable } from '@angular/core';
 
-import { Observable, of, Subject } from 'rxjs';
+import { BehaviorSubject, Observable } from 'rxjs';
+import { filter } from 'rxjs/operators';
 
 import { WebsocketService } from './websocket.service';
 
@@ -28,17 +29,12 @@ export class ConstantsService {
     /**
      * The constants
      */
-    private constants: Constants;
-
-    /**
-     * Flag, if constants are requested, but the server hasn't send them yet.
-     */
-    private pending = false;
+    private constants: Constants = {};
 
     /**
      * Pending requests will be notified by these subjects, one per key.
      */
-    private pendingSubject: { [key: string]: Subject<any> } = {};
+    private subjects: { [key: string]: BehaviorSubject<any> } = {};
 
     /**
      * @param websocketService
@@ -47,29 +43,16 @@ export class ConstantsService {
         // The hook for recieving constants.
         websocketService.getOberservable<Constants>('constants').subscribe(constants => {
             this.constants = constants;
-            if (this.pending) {
-                // send constants to subscribers that await constants.
-                this.pending = false;
-                this.informSubjects();
-            }
+            Object.keys(this.subjects).forEach(key => {
+                this.subjects[key].next(this.constants[key]);
+            });
         });
 
         // We can request constants, if the websocket connection opens.
         // On retries, the `refresh()` method is called by the OpenSlidesService, so
         // here we do not need to take care about this.
         websocketService.noRetryConnectEvent.subscribe(() => {
-            if (this.pending) {
-                this.websocketService.send('constants', {});
-            }
-        });
-    }
-
-    /**
-     * Inform subjects about changes.
-     */
-    private informSubjects(): void {
-        Object.keys(this.pendingSubject).forEach(key => {
-            this.pendingSubject[key].next(this.constants[key]);
+            this.refresh();
         });
     }
 
@@ -78,32 +61,19 @@ export class ConstantsService {
      * @param key The constant to get.
      */
     public get<T>(key: string): Observable<T> {
-        if (this.constants) {
-            return of(this.constants[key]);
-        } else {
-            // we have to request constants.
-            if (!this.pending) {
-                this.pending = true;
-                // if the connection is open, we directly can send the request.
-                if (this.websocketService.isConnected) {
-                    this.websocketService.send('constants', {});
-                }
-            }
-            if (!this.pendingSubject[key]) {
-                this.pendingSubject[key] = new Subject<any>();
-            }
-            return this.pendingSubject[key].asObservable() as Observable<T>;
+        if (!this.subjects[key]) {
+            this.subjects[key] = new BehaviorSubject<any>(this.constants[key]);
         }
+        return this.subjects[key].asObservable().pipe(filter(x => !!x));
     }
 
     /**
      * Refreshed the constants
      */
-    public async refresh(): Promise<void> {
+    public refresh(): Promise<void> {
         if (!this.websocketService.isConnected) {
             return;
         }
-        this.constants = await this.websocketService.sendAndGetResponse('constants', {});
-        this.informSubjects();
+        this.websocketService.send('constants', {});
     }
 }
diff --git a/client/src/app/core/core-services/data-store-upgrade.service.ts b/client/src/app/core/core-services/data-store-upgrade.service.ts
index 58eb74766..bc7e9e51e 100644
--- a/client/src/app/core/core-services/data-store-upgrade.service.ts
+++ b/client/src/app/core/core-services/data-store-upgrade.service.ts
@@ -1,12 +1,23 @@
 import { Injectable } from '@angular/core';
 
-import { take } from 'rxjs/operators';
-
 import { AutoupdateService } from './autoupdate.service';
 import { ConstantsService } from './constants.service';
 import { StorageService } from './storage.service';
 
-const DB_SCHEMA_VERSION = 'DbSchemaVersion';
+interface SchemaVersion {
+    db: string;
+    config: number;
+    migration: number;
+}
+
+function isSchemaVersion(obj: any): obj is SchemaVersion {
+    if (!obj || typeof obj !== 'object') {
+        return false;
+    }
+    return obj.db !== undefined && obj.config !== undefined && obj.migration !== undefined;
+}
+
+const SCHEMA_VERSION = 'SchemaVersion';
 
 /**
  * Manages upgrading the DataStore, if the migration version from the server is higher than the current one.
@@ -25,24 +36,47 @@ export class DataStoreUpgradeService {
         private constantsService: ConstantsService,
         private storageService: StorageService
     ) {
-        this.checkForUpgrade();
+        // Prevent the schema version to be cleard. This is important
+        // after a reset from OpenSlides, because the complete data is
+        // queried from the server and we do not want also to trigger a reload
+        // by changing the schema from null -> <schema>.
+        this.storageService.addNoClearKey(SCHEMA_VERSION);
+
+        this.constantsService
+            .get<SchemaVersion>(SCHEMA_VERSION)
+            .subscribe(serverVersion => this.checkForUpgrade(serverVersion));
     }
 
-    public async checkForUpgrade(): Promise<boolean> {
-        const version = await this.constantsService
-            .get<string | number>(DB_SCHEMA_VERSION)
-            .pipe(take(1))
-            .toPromise();
-        console.log('DB schema version:', version);
-        const currentVersion = await this.storageService.get<string>(DB_SCHEMA_VERSION);
-        await this.storageService.set(DB_SCHEMA_VERSION, version);
-        const doUpgrade = version !== currentVersion;
+    public async checkForUpgrade(serverVersion: SchemaVersion): Promise<boolean> {
+        console.log('Server schema version:', serverVersion);
+        const clientVersion = await this.storageService.get<SchemaVersion>(SCHEMA_VERSION);
+        await this.storageService.set(SCHEMA_VERSION, serverVersion);
 
-        if (doUpgrade) {
-            console.log(`DB schema version changed from ${currentVersion} to ${version}`);
-            await this.autoupdateService.doFullUpdate();
+        let doUpgrade = false;
+        if (isSchemaVersion(clientVersion)) {
+            if (clientVersion.db !== serverVersion.db) {
+                console.log(`\tDB id changed from ${clientVersion.db} to ${serverVersion.db}`);
+                doUpgrade = true;
+            }
+            if (clientVersion.config !== serverVersion.config) {
+                console.log(`\tConfig changed from ${clientVersion.config} to ${serverVersion.config}`);
+                doUpgrade = true;
+            }
+            if (clientVersion.migration !== serverVersion.migration) {
+                console.log(`\tMigration changed from ${clientVersion.migration} to ${serverVersion.migration}`);
+                doUpgrade = true;
+            }
+        } else {
+            console.log('\tNo client schema version.');
+            doUpgrade = true;
         }
 
+        if (doUpgrade) {
+            console.log('\t-> In result of a schema version change: Do full update.');
+            await this.autoupdateService.doFullUpdate();
+        } else {
+            console.log('\t-> No upgrade needed.');
+        }
         return doUpgrade;
     }
 }
diff --git a/client/src/app/core/core-services/openslides.service.ts b/client/src/app/core/core-services/openslides.service.ts
index c3c958bda..093998101 100644
--- a/client/src/app/core/core-services/openslides.service.ts
+++ b/client/src/app/core/core-services/openslides.service.ts
@@ -3,7 +3,6 @@ import { Router } from '@angular/router';
 
 import { AutoupdateService } from './autoupdate.service';
 import { ConstantsService } from './constants.service';
-import { DataStoreUpgradeService } from './data-store-upgrade.service';
 import { DataStoreService } from './data-store.service';
 import { OperatorService } from './operator.service';
 import { StorageService } from './storage.service';
@@ -47,8 +46,7 @@ export class OpenSlidesService {
         private router: Router,
         private autoupdateService: AutoupdateService,
         private DS: DataStoreService,
-        private constantsService: ConstantsService,
-        private dataStoreUpgradeService: DataStoreUpgradeService
+        private constantsService: ConstantsService
     ) {
         // Handler that gets called, if the websocket connection reconnects after a disconnection.
         // There might have changed something on the server, so we check the operator, if he changed.
@@ -162,6 +160,7 @@ export class OpenSlidesService {
         const response = await this.operator.whoAmI();
         // User logged off.
         if (!response.user && !response.guest_enabled) {
+            this.websocketService.cancelReconnectenRetry();
             await this.shutdown();
             this.redirectToLoginIfNotSubpage();
         } else {
@@ -174,24 +173,9 @@ export class OpenSlidesService {
                 await this.reboot();
             } else if (requestChanges) {
                 // User is still the same, but check for missed autoupdates.
-                await this.recoverAfterReconnect();
+                this.autoupdateService.requestChanges();
+                this.constantsService.refresh();
             }
         }
     }
-
-    /**
-     * The cache-refresh strategy, if there was an reconnect and the user didn't changed.
-     */
-    private async recoverAfterReconnect(): Promise<void> {
-        // Reload constants to get either new one (in general) and especially
-        // the "DbSchemaVersion" one, to check, if the DB has changed (e.g. due
-        // to an update)
-        await this.constantsService.refresh();
-
-        // If the DB schema version didn't change, request normal changes.
-        // If so, then a full update is implicit triggered, so we do not need to to anything.
-        if (!(await this.dataStoreUpgradeService.checkForUpgrade())) {
-            this.autoupdateService.requestChanges();
-        }
-    }
 }
diff --git a/client/src/app/core/core-services/storage.service.ts b/client/src/app/core/core-services/storage.service.ts
index 54c7815ea..f8caa1094 100644
--- a/client/src/app/core/core-services/storage.service.ts
+++ b/client/src/app/core/core-services/storage.service.ts
@@ -13,12 +13,18 @@ import { OpenSlidesStatusService } from './openslides-status.service';
     providedIn: 'root'
 })
 export class StorageService {
+    private noClearKeys: string[] = [];
+
     /**
      * Constructor to create the StorageService. Needs the localStorage service.
      * @param localStorage
      */
     public constructor(private localStorage: LocalStorage, private OSStatus: OpenSlidesStatusService) {}
 
+    public addNoClearKey(key: string): void {
+        this.noClearKeys.push(key);
+    }
+
     /**
      * Sets the item into the store asynchronously.
      * @param key
@@ -57,13 +63,20 @@ export class StorageService {
     }
 
     /**
-     * Clear the whole cache
+     * Clear the whole cache except for keys given in `addNoClearKey`.
      */
     public async clear(): Promise<void> {
         this.assertNotHistoryMode();
+        const savedData: { [key: string]: any } = {};
+        for (const key of this.noClearKeys) {
+            savedData[key] = await this.get(key);
+        }
         if (!(await this.localStorage.clear().toPromise())) {
             throw new Error('Could not clear the storage.');
         }
+        for (const key of this.noClearKeys) {
+            await this.set(key, savedData[key]);
+        }
     }
 
     /**
diff --git a/client/src/app/core/core-services/websocket.service.ts b/client/src/app/core/core-services/websocket.service.ts
index 582031b5e..af8352d87 100644
--- a/client/src/app/core/core-services/websocket.service.ts
+++ b/client/src/app/core/core-services/websocket.service.ts
@@ -182,6 +182,11 @@ export class WebsocketService {
      */
     private retryCounter = 0;
 
+    /**
+     * The timeout in the onClose-handler for the next reconnect retry.
+     */
+    private retryTimeout: any = null;
+
     /**
      * Constructor that handles the router
      * @param matSnackBar
@@ -385,12 +390,20 @@ export class WebsocketService {
 
             // A random retry timeout between 2000 and 5000 ms.
             const timeout = Math.floor(Math.random() * 3000 + 2000);
-            setTimeout(() => {
+            this.retryTimeout = setTimeout(() => {
+                this.retryTimeout = null;
                 this.connect({ enableAutoupdates: true }, true);
             }, timeout);
         }
     }
 
+    public cancelReconnectenRetry(): void {
+        if (this.retryTimeout) {
+            clearTimeout(this.retryTimeout);
+            this.retryTimeout = null;
+        }
+    }
+
     private dismissConnectionErrorNotice(): void {
         if (this.connectionErrorNotice) {
             this.connectionErrorNotice.dismiss();
diff --git a/openslides/core/apps.py b/openslides/core/apps.py
index e7728e512..7f6fe8497 100644
--- a/openslides/core/apps.py
+++ b/openslides/core/apps.py
@@ -1,4 +1,3 @@
-import hashlib
 import logging
 import os
 import sys
@@ -8,11 +7,9 @@ from typing import Any, Dict, List
 
 from django.apps import AppConfig
 from django.conf import settings
-from django.db.models import Max
 from django.db.models.signals import post_migrate, pre_delete
 
-
-logger = logging.getLogger("openslides.core")
+from openslides.utils.schema_version import schema_version_handler
 
 
 class CoreAppConfig(AppConfig):
@@ -179,18 +176,7 @@ class CoreAppConfig(AppConfig):
             config_groups[-1]["subgroups"][-1]["items"].append(config_variable.data)
         constants["ConfigVariables"] = config_groups
 
-        # get max migration id -> the "version" of the DB
-        from django.db.migrations.recorder import MigrationRecorder
-
-        migration_version = MigrationRecorder.Migration.objects.aggregate(Max("id"))[
-            "id__max"
-        ]
-        config_version = config["config_version"]
-        hash = hashlib.sha1(
-            f"{migration_version}#{config_version}".encode()
-        ).hexdigest()
-        constants["DbSchemaVersion"] = hash
-        logger.info(f"DbSchemaVersion={hash}")
+        constants["SchemaVersion"] = schema_version_handler.get()
 
         return constants
 
@@ -209,6 +195,7 @@ def manage_config(**kwargs):
     altered = config.cleanup_old_config_values() or altered
     if altered:
         config.increment_version()
+        logging.getLogger(__name__).info("Updated config variables")
 
 
 def startup():
@@ -224,6 +211,6 @@ def startup():
     from openslides.utils.cache import element_cache
     from openslides.core.models import History
 
-    element_cache.ensure_cache()
+    element_cache.ensure_schema_version()
     set_constants(get_constants_from_apps())
     History.objects.build_history()
diff --git a/openslides/core/config.py b/openslides/core/config.py
index 6525531e7..cd2f7c93e 100644
--- a/openslides/core/config.py
+++ b/openslides/core/config.py
@@ -49,7 +49,7 @@ class ConfigHandler:
         if not self.exists(key):
             raise ConfigNotFound(f"The config variable {key} was not found.")
 
-        return async_to_sync(element_cache.get_element_full_data)(
+        return async_to_sync(element_cache.get_element_data)(
             self.get_collection_string(), self.get_key_to_id()[key]
         )["value"]
 
@@ -85,7 +85,7 @@ class ConfigHandler:
             if self.key_to_id is not None:
                 return
 
-        config_full_data = await element_cache.get_collection_full_data(
+        config_full_data = await element_cache.get_collection_data(
             self.get_collection_string()
         )
         elements = config_full_data.values()
diff --git a/openslides/core/config_variables.py b/openslides/core/config_variables.py
index 6ab131242..84f6a4b1a 100644
--- a/openslides/core/config_variables.py
+++ b/openslides/core/config_variables.py
@@ -1,3 +1,5 @@
+import uuid
+
 from django.core.validators import MaxLengthValidator
 
 from openslides.core.config import ConfigVariable
@@ -394,7 +396,7 @@ def get_config_variables():
         group="Custom translations",
     )
 
-    # Config version
+    # Config version and DB id
     yield ConfigVariable(
         name="config_version",
         input_type="integer",
@@ -402,3 +404,10 @@ def get_config_variables():
         group="Version",
         hidden=True,
     )
+    yield ConfigVariable(
+        name="db_id",
+        input_type="string",
+        default_value=uuid.uuid4().hex,
+        group="Version",
+        hidden=True,
+    )
diff --git a/openslides/core/models.py b/openslides/core/models.py
index 351d48bcc..393ab0796 100644
--- a/openslides/core/models.py
+++ b/openslides/core/models.py
@@ -287,7 +287,7 @@ class HistoryManager(models.Manager):
         instances = None
         if self.all().count() == 0:
             elements = []
-            all_full_data = async_to_sync(element_cache.get_all_full_data)()
+            all_full_data = async_to_sync(element_cache.get_all_data_list)()
             for collection_string, data in all_full_data.items():
                 for full_data in data:
                     elements.append(
diff --git a/openslides/core/views.py b/openslides/core/views.py
index 11f71b968..620366d3d 100644
--- a/openslides/core/views.py
+++ b/openslides/core/views.py
@@ -608,7 +608,7 @@ class HistoryDataView(utils_views.APIView):
         )
         missing_keys = all_current_config_keys - all_old_config_keys
         if missing_keys:
-            config_full_data = async_to_sync(element_cache.get_collection_full_data)(
+            config_full_data = async_to_sync(element_cache.get_collection_data)(
                 "core/config"
             )
             key_to_id = config.get_key_to_id()
diff --git a/openslides/core/websocket.py b/openslides/core/websocket.py
index 8558c4792..5739d04af 100644
--- a/openslides/core/websocket.py
+++ b/openslides/core/websocket.py
@@ -5,11 +5,9 @@ from ..utils.constants import get_constants
 from ..utils.projector import get_projector_data
 from ..utils.stats import WebsocketLatencyLogger
 from ..utils.websocket import (
-    WEBSOCKET_CHANGE_ID_TOO_HIGH,
     WEBSOCKET_NOT_AUTHORIZED,
     BaseWebsocketClientMessage,
     ProtocollAsyncJsonWebsocketConsumer,
-    get_element_data,
 )
 
 
@@ -116,18 +114,7 @@ class GetElementsWebsocketClientMessage(BaseWebsocketClientMessage):
         self, consumer: "ProtocollAsyncJsonWebsocketConsumer", content: Any, id: str
     ) -> None:
         requested_change_id = content.get("change_id", 0)
-        try:
-            element_data = await get_element_data(
-                consumer.scope["user"]["id"], requested_change_id
-            )
-        except ValueError as error:
-            await consumer.send_error(
-                code=WEBSOCKET_CHANGE_ID_TOO_HIGH, message=str(error), in_response=id
-            )
-        else:
-            await consumer.send_json(
-                type="autoupdate", content=element_data, in_response=id
-            )
+        await consumer.send_autoupdate(requested_change_id, in_response=id)
 
 
 class AutoupdateWebsocketClientMessage(BaseWebsocketClientMessage):
diff --git a/openslides/users/views.py b/openslides/users/views.py
index caadede9a..d1290d625 100644
--- a/openslides/users/views.py
+++ b/openslides/users/views.py
@@ -130,8 +130,6 @@ class UserViewSet(ModelViewSet):
                 if key not in ("username", "about_me"):
                     del request.data[key]
         response = super().update(request, *args, **kwargs)
-        # Maybe some group assignments have changed. Better delete the restricted user cache
-        async_to_sync(element_cache.del_user)(user.pk)
         return response
 
     def destroy(self, request, *args, **kwargs):
@@ -275,8 +273,6 @@ class UserViewSet(ModelViewSet):
                 user.groups.add(*groups)
             else:
                 user.groups.remove(*groups)
-            # Maybe some group assignments have changed. Better delete the restricted user cache
-            async_to_sync(element_cache.del_user)(user.pk)
 
         inform_changed_data(users)
         return Response()
@@ -570,13 +566,9 @@ class GroupViewSet(ModelViewSet):
         if not changed_permissions:
             return  # either None or empty list.
 
-        # Delete the user chaches of all affected users
-        for user in group.user_set.all():
-            async_to_sync(element_cache.del_user)(user.pk)
-
         elements: List[Element] = []
         signal_results = permission_change.send(None, permissions=changed_permissions)
-        all_full_data = async_to_sync(element_cache.get_all_full_data)()
+        all_full_data = async_to_sync(element_cache.get_all_data_list)()
         for _, signal_collections in signal_results:
             for cachable in signal_collections:
                 for full_data in all_full_data.get(
@@ -672,8 +664,8 @@ class WhoAmIDataView(APIView):
         guest_enabled = anonymous_is_enabled()
 
         if user_id:
-            user_data = async_to_sync(element_cache.get_element_restricted_data)(
-                user_id, self.request.user.get_collection_string(), user_id
+            user_data = async_to_sync(element_cache.get_element_data)(
+                self.request.user.get_collection_string(), user_id, user_id
             )
             group_ids = user_data["groups_id"] or [GROUP_DEFAULT_PK]
         else:
@@ -682,9 +674,7 @@ class WhoAmIDataView(APIView):
 
         # collect all permissions
         permissions: Set[str] = set()
-        group_all_data = async_to_sync(element_cache.get_collection_full_data)(
-            "users/group"
-        )
+        group_all_data = async_to_sync(element_cache.get_collection_data)("users/group")
         for group_id in group_ids:
             permissions.update(group_all_data[group_id]["permissions"])
 
diff --git a/openslides/utils/access_permissions.py b/openslides/utils/access_permissions.py
index 2a27c3a74..1fb547e13 100644
--- a/openslides/utils/access_permissions.py
+++ b/openslides/utils/access_permissions.py
@@ -86,16 +86,14 @@ class RequiredUsers:
         user_ids: Set[int] = set()
 
         for collection_string in collection_strings:
-            collection_full_data = await element_cache.get_collection_full_data(
-                collection_string
-            )
+            collection_data = await element_cache.get_collection_data(collection_string)
             # Get the callable for the collection_string
             get_user_ids = self.callables.get(collection_string)
-            if not (get_user_ids and collection_full_data):
+            if not (get_user_ids and collection_data):
                 # if the collection_string is unknown or it has no data, do nothing
                 continue
 
-            for element in collection_full_data.values():
+            for element in collection_data.values():
                 user_ids.update(get_user_ids(element))
 
         return user_ids
diff --git a/openslides/utils/auth.py b/openslides/utils/auth.py
index 102264d00..bfadeb6d9 100644
--- a/openslides/utils/auth.py
+++ b/openslides/utils/auth.py
@@ -67,14 +67,14 @@ async def async_has_perm(user_id: int, perm: str) -> bool:
         has_perm = False
     elif not user_id:
         # Use the permissions from the default group.
-        default_group = await element_cache.get_element_full_data(
+        default_group = await element_cache.get_element_data(
             group_collection_string, GROUP_DEFAULT_PK
         )
         if default_group is None:
             raise RuntimeError("Default Group does not exist.")
         has_perm = perm in default_group["permissions"]
     else:
-        user_data = await element_cache.get_element_full_data(
+        user_data = await element_cache.get_element_data(
             user_collection_string, user_id
         )
         if user_data is None:
@@ -87,7 +87,7 @@ async def async_has_perm(user_id: int, perm: str) -> bool:
             # permission. If the user has no groups, then use the default group.
             group_ids = user_data["groups_id"] or [GROUP_DEFAULT_PK]
             for group_id in group_ids:
-                group = await element_cache.get_element_full_data(
+                group = await element_cache.get_element_data(
                     group_collection_string, group_id
                 )
                 if group is None:
@@ -131,7 +131,7 @@ async def async_in_some_groups(user_id: int, groups: List[int]) -> bool:
         # Use the permissions from the default group.
         in_some_groups = GROUP_DEFAULT_PK in groups
     else:
-        user_data = await element_cache.get_element_full_data(
+        user_data = await element_cache.get_element_data(
             user_collection_string, user_id
         )
         if user_data is None:
@@ -167,7 +167,7 @@ async def async_anonymous_is_enabled() -> bool:
     """
     from ..core.config import config
 
-    element = await element_cache.get_element_full_data(
+    element = await element_cache.get_element_data(
         config.get_collection_string(),
         (await config.async_get_key_to_id())["general_system_enable_anonymous"],
     )
diff --git a/openslides/utils/cache.py b/openslides/utils/cache.py
index 93260e056..64673b3c6 100644
--- a/openslides/utils/cache.py
+++ b/openslides/utils/cache.py
@@ -1,4 +1,3 @@
-import asyncio
 import json
 import logging
 from collections import defaultdict
@@ -7,42 +6,54 @@ from time import sleep
 from typing import Any, Callable, Dict, List, Optional, Tuple, Type
 
 from asgiref.sync import async_to_sync
-from django.conf import settings
+from django.apps import apps
 
 from .cache_providers import (
     Cachable,
     ElementCacheProvider,
     MemmoryCacheProvider,
     RedisCacheProvider,
-    get_all_cachables,
 )
 from .redis import use_redis
+from .schema_version import SchemaVersion, schema_version_handler
 from .utils import get_element_id, split_element_id
 
 
 logger = logging.getLogger(__name__)
 
 
+def get_all_cachables() -> List[Cachable]:
+    """
+    Returns all element of OpenSlides.
+    """
+    out: List[Cachable] = []
+    for app in apps.get_app_configs():
+        try:
+            # Get the method get_startup_elements() from an app.
+            # This method has to return an iterable of Cachable objects.
+            get_startup_elements = app.get_startup_elements
+        except AttributeError:
+            # Skip apps that do not implement get_startup_elements.
+            continue
+        out.extend(get_startup_elements())
+    return out
+
+
 class ElementCache:
     """
     Cache for the elements.
 
-    Saves the full_data and if enabled the restricted data.
+    Saves the full_data
 
-    There is one redis Hash (simular to python dict) for the full_data and one
-    Hash for every user.
+    There is one redis Hash (simular to python dict) for the full_data
 
     The key of the Hashes is COLLECTIONSTRING:ID where COLLECTIONSTRING is the
     collection_string of a collection and id the id of an element.
 
-    All elements have to be in the cache. If one element is missing, the cache
-    is invalid, but this can not be detected. When a plugin with a new
-    collection is added to OpenSlides, then the cache has to be rebuild manualy.
-
     There is an sorted set in redis with the change id as score. The values are
     COLLETIONSTRING:ID for the elements that have been changed with that change
-    id. With this key it is possible, to get all elements as full_data or as
-    restricted_data that are newer then a specific change id.
+    id. With this key it is possible, to get all elements as full_data
+    that are newer then a specific change id.
 
     All method of this class are async. You either have to call them with
     await in an async environment or use asgiref.sync.async_to_sync().
@@ -50,36 +61,34 @@ class ElementCache:
 
     def __init__(
         self,
-        use_restricted_data_cache: bool = False,
         cache_provider_class: Type[ElementCacheProvider] = RedisCacheProvider,
         cachable_provider: Callable[[], List[Cachable]] = get_all_cachables,
-        start_time: int = None,
+        default_change_id: Optional[int] = None,
     ) -> None:
         """
         Initializes the cache.
-
-        When restricted_data_cache is false, no restricted data is saved.
         """
-        self.use_restricted_data_cache = use_restricted_data_cache
-        self.cache_provider = cache_provider_class()
+        self.cache_provider = cache_provider_class(self.async_ensure_cache)
         self.cachable_provider = cachable_provider
         self._cachables: Optional[Dict[str, Cachable]] = None
+        self.set_default_change_id(default_change_id)
 
-        # Start time is used as first change_id if there is non in redis
-        if start_time is None:
+    def set_default_change_id(self, default_change_id: Optional[int] = None) -> None:
+        """
+        Sets the default change id for the cache. Needs to update, if the cache gets generated.
+        """
+        # The current time is used as the first change_id if there is non in redis
+        if default_change_id is None:
             # Use the miliseconds (rounted) since the 2016-02-29.
-            start_time = (
+            default_change_id = (
                 int((datetime.utcnow() - datetime(2016, 2, 29)).total_seconds()) * 1000
             )
-        self.start_time = start_time
-
-        # Tells if self.ensure_cache was called.
-        self.ensured = False
+        self.default_change_id = default_change_id
 
     @property
     def cachables(self) -> Dict[str, Cachable]:
         """
-        Returns all Cachables as a dict where the key is the collection_string of the cachable.
+        Returns all cachables as a dict where the key is the collection_string of the cachable.
         """
         # This method is neccessary to lazy load the cachables
         if self._cachables is None:
@@ -89,45 +98,71 @@ class ElementCache:
             }
         return self._cachables
 
-    def ensure_cache(self, reset: bool = False) -> None:
+    def ensure_cache(
+        self, reset: bool = False, default_change_id: Optional[int] = None
+    ) -> None:
         """
-        Makes sure that the cache exist.
-
-        Builds the cache if not. If reset is True, it will be reset in any case.
-
-        This method is sync, so it can be run when OpenSlides starts.
+        Ensures the existance of the cache; see async_ensure_cache for more info.
         """
-        cache_exists = async_to_sync(self.cache_provider.data_exists)()
+        async_to_sync(self.async_ensure_cache)(reset, default_change_id)
+
+    async def async_ensure_cache(
+        self, reset: bool = False, default_change_id: Optional[int] = None
+    ) -> None:
+        """
+        Makes sure that the cache exist. Builds the cache if not or reset is given as True.
+        """
+        cache_exists = await self.cache_provider.data_exists()
 
         if reset or not cache_exists:
-            lock_name = "ensure_cache"
-            # Set a lock so only one process builds the cache
-            if async_to_sync(self.cache_provider.set_lock)(lock_name):
-                logger.info("Building up the cache data...")
-                try:
-                    mapping = {}
-                    for collection_string, cachable in self.cachables.items():
-                        for element in cachable.get_elements():
-                            mapping.update(
-                                {
-                                    get_element_id(
-                                        collection_string, element["id"]
-                                    ): json.dumps(element)
-                                }
-                            )
-                    logger.info("Done building the cache data.")
-                    logger.info("Saving cache data into the cache...")
-                    async_to_sync(self.cache_provider.reset_full_cache)(mapping)
-                    logger.info("Done saving the cache data.")
-                finally:
-                    async_to_sync(self.cache_provider.del_lock)(lock_name)
-            else:
-                logger.info("Wait for another process to build up the cache...")
-                while async_to_sync(self.cache_provider.get_lock)(lock_name):
-                    sleep(0.01)
-                logger.info("Cache is ready (built by another process).")
+            await self.build_cache(default_change_id)
 
-        self.ensured = True
+    def ensure_schema_version(self) -> None:
+        async_to_sync(self.async_ensure_schema_version)()
+
+    async def async_ensure_schema_version(self) -> None:
+        cache_schema_version = await self.cache_provider.get_schema_version()
+        schema_changed = not schema_version_handler.compare(cache_schema_version)
+        schema_version_handler.log_current()
+
+        cache_exists = await self.cache_provider.data_exists()
+        if schema_changed or not cache_exists:
+            await self.build_cache(schema_version=schema_version_handler.get())
+
+    async def build_cache(
+        self,
+        default_change_id: Optional[int] = None,
+        schema_version: Optional[SchemaVersion] = None,
+    ) -> None:
+        lock_name = "build_cache"
+        # Set a lock so only one process builds the cache
+        if await self.cache_provider.set_lock(lock_name):
+            logger.info("Building up the cache data...")
+            try:
+                mapping = {}
+                for collection_string, cachable in self.cachables.items():
+                    for element in cachable.get_elements():
+                        mapping.update(
+                            {
+                                get_element_id(
+                                    collection_string, element["id"]
+                                ): json.dumps(element)
+                            }
+                        )
+                logger.info("Done building the cache data.")
+                logger.info("Saving cache data into the cache...")
+                self.set_default_change_id(default_change_id=default_change_id)
+                await self.cache_provider.reset_full_cache(mapping)
+                if schema_version:
+                    await self.cache_provider.set_schema_version(schema_version)
+                logger.info("Done saving the cache data.")
+            finally:
+                await self.cache_provider.del_lock(lock_name)
+        else:
+            logger.info("Wait for another process to build up the cache...")
+            while await self.cache_provider.get_lock(lock_name):
+                sleep(0.01)
+            logger.info("Cache is ready (built by another process).")
 
     async def change_elements(
         self, elements: Dict[str, Optional[Dict[str, Any]]]
@@ -135,16 +170,12 @@ class ElementCache:
         """
         Changes elements in the cache.
 
-        elements is a list of the changed elements as dict. When the value is None,
-        it is interpreded as deleted. The key has to be an element_id.
+        elements is a dict with element_id <-> changed element. When the value is None,
+        it is interpreded as deleted.
 
         Returns the new generated change_id.
         """
-        if not self.ensured:
-            raise RuntimeError(
-                "Call element_cache.ensure_cache before changing elements."
-            )
-
+        # Split elements into changed and deleted.
         deleted_elements = []
         changed_elements = []
         for element_id, data in elements.items():
@@ -155,47 +186,90 @@ class ElementCache:
             else:
                 deleted_elements.append(element_id)
 
-        if changed_elements:
-            await self.cache_provider.add_elements(changed_elements)
-        if deleted_elements:
-            await self.cache_provider.del_elements(deleted_elements)
-
         return await self.cache_provider.add_changed_elements(
-            self.start_time + 1, elements.keys()
+            changed_elements, deleted_elements, self.default_change_id + 1
         )
 
-    async def get_all_full_data(self) -> Dict[str, List[Dict[str, Any]]]:
+    async def get_all_data_list(
+        self, user_id: Optional[int] = None
+    ) -> Dict[str, List[Dict[str, Any]]]:
         """
-        Returns all full_data.
+        Returns all data with a list per collection:
+        {
+            <collection>: [<element>, <element>, ...]
+        }
+        If the user id is given the data will be restricted for this user.
+        """
+        all_data: Dict[str, List[Dict[str, Any]]] = defaultdict(list)
+        for element_id, data in (await self.cache_provider.get_all_data()).items():
+            collection_string, _ = split_element_id(element_id)
+            all_data[collection_string].append(json.loads(data.decode()))
 
-        The returned value is a dict where the key is the collection_string and
-        the value is a list of data.
-        """
-        all_data = await self.get_all_full_data_ordered()
-        out: Dict[str, List[Dict[str, Any]]] = defaultdict(list)
-        for collection_string, collection_data in all_data.items():
-            for data in collection_data.values():
-                out[collection_string].append(data)
-        return dict(out)
+        if user_id is not None:
+            for collection_string in all_data.keys():
+                restricter = self.cachables[collection_string].restrict_elements
+                all_data[collection_string] = await restricter(
+                    user_id, all_data[collection_string]
+                )
+        return dict(all_data)
 
-    async def get_all_full_data_ordered(self) -> Dict[str, Dict[int, Dict[str, Any]]]:
+    async def get_all_data_dict(self) -> Dict[str, Dict[int, Dict[str, Any]]]:
         """
-        Like get_all_full_data but orders the element of one collection by there
-        id.
+        Returns all data with a dict (id <-> element) per collection:
+        {
+            <collection>: {
+                <id>: <element>
+            }
+        }
         """
-        out: Dict[str, Dict[int, Dict[str, Any]]] = defaultdict(dict)
-        full_data = await self.cache_provider.get_all_data()
-        for element_id, data in full_data.items():
+        all_data: Dict[str, Dict[int, Dict[str, Any]]] = defaultdict(dict)
+        for element_id, data in (await self.cache_provider.get_all_data()).items():
             collection_string, id = split_element_id(element_id)
-            out[collection_string][id] = json.loads(data.decode())
-        return dict(out)
+            all_data[collection_string][id] = json.loads(data.decode())
+        return dict(all_data)
 
-    async def get_full_data(
-        self, change_id: int = 0, max_change_id: int = -1
+    async def get_collection_data(
+        self, collection_string: str
+    ) -> Dict[int, Dict[str, Any]]:
+        """
+        Returns the data for one collection as dict: {id: <element>}
+        """
+        encoded_collection_data = await self.cache_provider.get_collection_data(
+            collection_string
+        )
+        collection_data = {}
+        for id in encoded_collection_data.keys():
+            collection_data[id] = json.loads(encoded_collection_data[id].decode())
+        return collection_data
+
+    async def get_element_data(
+        self, collection_string: str, id: int, user_id: Optional[int] = None
+    ) -> Optional[Dict[str, Any]]:
+        """
+        Returns one element or None, if the element does not exist.
+        If the user id is given the data will be restricted for this user.
+        """
+        encoded_element = await self.cache_provider.get_element_data(
+            get_element_id(collection_string, id)
+        )
+
+        if encoded_element is None:
+            return None
+        element = json.loads(encoded_element.decode())  # type: ignore
+
+        if user_id is not None:
+            restricter = self.cachables[collection_string].restrict_elements
+            restricted_elements = await restricter(user_id, [element])
+            element = restricted_elements[0] if restricted_elements else None
+        return element
+
+    async def get_data_since(
+        self, user_id: Optional[int] = None, change_id: int = 0, max_change_id: int = -1
     ) -> Tuple[Dict[str, List[Dict[str, Any]]], List[str]]:
         """
-        Returns all full_data since change_id until max_change_id (including).
-        max_change_id -1 means the highest change_id.
+        Returns all data since change_id until max_change_id (included).
+        max_change_id -1 means the highest change_id. If the user id is given the
+        data will be restricted for this user.
 
         Returns two values inside a tuple. The first value is a dict where the
         key is the collection_string and the value is a list of data. The second
@@ -210,7 +284,7 @@ class ElementCache:
         that the cache does not know about.
         """
         if change_id == 0:
-            return (await self.get_all_full_data(), [])
+            return (await self.get_all_data_list(user_id), [])
 
         # This raises a Runtime Exception, if there is no change_id
         lowest_change_id = await self.get_lowest_change_id()
@@ -226,245 +300,39 @@ class ElementCache:
         raw_changed_elements, deleted_elements = await self.cache_provider.get_data_since(
             change_id, max_change_id=max_change_id
         )
-        return (
-            {
-                collection_string: [json.loads(value.decode()) for value in value_list]
-                for collection_string, value_list in raw_changed_elements.items()
-            },
-            deleted_elements,
-        )
+        changed_elements = {
+            collection_string: [json.loads(value.decode()) for value in value_list]
+            for collection_string, value_list in raw_changed_elements.items()
+        }
 
-    async def get_collection_full_data(
-        self, collection_string: str
-    ) -> Dict[int, Dict[str, Any]]:
-        full_data = await self.cache_provider.get_collection_data(collection_string)
-        out = {}
-        for element_id, data in full_data.items():
-            returned_collection_string, id = split_element_id(element_id)
-            if returned_collection_string == collection_string:
-                out[id] = json.loads(data.decode())
-        return out
-
-    async def get_element_full_data(
-        self, collection_string: str, id: int
-    ) -> Optional[Dict[str, Any]]:
-        """
-        Returns one element as full data.
-
-        Returns None if the element does not exist.
-        """
-        element = await self.cache_provider.get_element(
-            get_element_id(collection_string, id)
-        )
-
-        if element is None:
-            return None
-        return json.loads(element.decode())
-
-    async def exists_restricted_data(self, user_id: int) -> bool:
-        """
-        Returns True, if the restricted_data exists for the user.
-        """
-        if not self.use_restricted_data_cache:
-            return False
-
-        return await self.cache_provider.data_exists(user_id)
-
-    async def del_user(self, user_id: int) -> None:
-        """
-        Removes one user from the resticted_data_cache.
-        """
-        await self.cache_provider.del_restricted_data(user_id)
-
-    async def update_restricted_data(self, user_id: int) -> None:
-        """
-        Updates the restricted data for an user from the full_data_cache.
-        """
-        # TODO: When elements are changed at the same time then this method run
-        #       this could make the cache invalid.
-        #       This could be fixed when get_full_data would be used with a
-        #       max change_id.
-        if not self.use_restricted_data_cache:
-            # If the restricted_data_cache is not used, there is nothing to do
-            return
-
-        if not self.ensured:
-            raise RuntimeError(
-                "Call element_cache.ensure_cache before updating restricted data."
-            )
-
-        # Try to write a special key.
-        # If this succeeds, there is noone else currently updating the cache.
-        # TODO: Make a timeout. Else this could block forever
-        lock_name = f"restricted_data_{user_id}"
-        if await self.cache_provider.set_lock(lock_name):
-            # Get change_id for this user
-            value = await self.cache_provider.get_change_id_user(user_id)
-            # If the change id is not in the cache yet, use -1 to get all data since 0
-            user_change_id = int(value) if value else -1
-            change_id = await self.get_current_change_id()
-            if change_id > user_change_id:
-                try:
-                    full_data_elements, deleted_elements = await self.get_full_data(
-                        user_change_id + 1
-                    )
-                except RuntimeError:
-                    # The user_change_id is lower then the lowest change_id in the cache.
-                    # The whole restricted_data for that user has to be recreated.
-                    full_data_elements = await self.get_all_full_data()
-                    deleted_elements = []
-                    await self.cache_provider.del_restricted_data(user_id)
-
-                mapping = {}
-                for collection_string, full_data in full_data_elements.items():
-                    restricter = self.cachables[collection_string].restrict_elements
-                    restricted_elements = await restricter(user_id, full_data)
-
-                    # find all elements the user can not see at all
-                    full_data_ids = set(element["id"] for element in full_data)
-                    restricted_data_ids = set(
-                        element["id"] for element in restricted_elements
-                    )
-                    for item_id in full_data_ids - restricted_data_ids:
-                        deleted_elements.append(
-                            get_element_id(collection_string, item_id)
-                        )
-
-                    for element in restricted_elements:
-                        # The user can see the element
-                        mapping.update(
-                            {
-                                get_element_id(
-                                    collection_string, element["id"]
-                                ): json.dumps(element)
-                            }
-                        )
-                mapping["_config:change_id"] = str(change_id)
-                await self.cache_provider.update_restricted_data(user_id, mapping)
-                # Remove deleted elements
-                if deleted_elements:
-                    await self.cache_provider.del_elements(deleted_elements, user_id)
-            # Unset the lock
-            await self.cache_provider.del_lock(lock_name)
-        else:
-            # Wait until the update if finshed
-            while await self.cache_provider.get_lock(lock_name):
-                await asyncio.sleep(0.01)
-
-    async def get_all_restricted_data(
-        self, user_id: int
-    ) -> Dict[str, List[Dict[str, Any]]]:
-        """
-        Like get_all_full_data but with restricted_data for an user.
-        """
-        if not self.use_restricted_data_cache:
-            all_restricted_data = {}
-            for collection_string, full_data in (
-                await self.get_all_full_data()
-            ).items():
+        if user_id is not None:
+            for collection_string, elements in changed_elements.items():
                 restricter = self.cachables[collection_string].restrict_elements
-                elements = await restricter(user_id, full_data)
-                all_restricted_data[collection_string] = elements
-            return all_restricted_data
-
-        await self.update_restricted_data(user_id)
-
-        out: Dict[str, List[Dict[str, Any]]] = defaultdict(list)
-        restricted_data = await self.cache_provider.get_all_data(user_id)
-        for element_id, data in restricted_data.items():
-            if element_id.decode().startswith("_config"):
-                continue
-            collection_string, __ = split_element_id(element_id)
-            out[collection_string].append(json.loads(data.decode()))
-        return dict(out)
-
-    async def get_restricted_data(
-        self, user_id: int, change_id: int = 0, max_change_id: int = -1
-    ) -> Tuple[Dict[str, List[Dict[str, Any]]], List[str]]:
-        """
-        Like get_full_data but with restricted_data for an user.
-        """
-        if change_id == 0:
-            # Return all data
-            return (await self.get_all_restricted_data(user_id), [])
-
-        if not self.use_restricted_data_cache:
-            changed_elements, deleted_elements = await self.get_full_data(
-                change_id, max_change_id
-            )
-            restricted_data = {}
-            for collection_string, full_data in changed_elements.items():
-                restricter = self.cachables[collection_string].restrict_elements
-                elements = await restricter(user_id, full_data)
+                restricted_elements = await restricter(user_id, elements)
 
                 # Add removed objects (through restricter) to deleted elements.
-                full_data_ids = set([data["id"] for data in full_data])
-                restricted_data_ids = set([data["id"] for data in elements])
-                for id in full_data_ids - restricted_data_ids:
+                element_ids = set([element["id"] for element in elements])
+                restricted_element_ids = set(
+                    [element["id"] for element in restricted_elements]
+                )
+                for id in element_ids - restricted_element_ids:
                     deleted_elements.append(get_element_id(collection_string, id))
 
-                if elements:
-                    restricted_data[collection_string] = elements
-            return restricted_data, deleted_elements
+                if not restricted_elements:
+                    del changed_elements[collection_string]
+                else:
+                    changed_elements[collection_string] = restricted_elements
 
-        lowest_change_id = await self.get_lowest_change_id()
-        if change_id < lowest_change_id:
-            # When change_id is lower then the lowest change_id in redis, we can
-            # not inform the user about deleted elements.
-            raise RuntimeError(
-                f"change_id {change_id} is lower then the lowest change_id in redis {lowest_change_id}. "
-                "Catch this exception and rerun the method with change_id=0."
-            )
-
-        # If another coroutine or another daphne server also updates the restricted
-        # data, this waits until it is done.
-        await self.update_restricted_data(user_id)
-
-        raw_changed_elements, deleted_elements = await self.cache_provider.get_data_since(
-            change_id, user_id, max_change_id
-        )
-        return (
-            {
-                collection_string: [json.loads(value.decode()) for value in value_list]
-                for collection_string, value_list in raw_changed_elements.items()
-            },
-            deleted_elements,
-        )
-
-    async def get_element_restricted_data(
-        self, user_id: int, collection_string: str, id: int
-    ) -> Optional[Dict[str, Any]]:
-        """
-        Returns the restricted_data of one element.
-
-        Returns None, if the element does not exists or the user has no permission to see it.
-        """
-        if not self.use_restricted_data_cache:
-            full_data = await self.get_element_full_data(collection_string, id)
-            if full_data is None:
-                return None
-            restricter = self.cachables[collection_string].restrict_elements
-            restricted_data = await restricter(user_id, [full_data])
-            return restricted_data[0] if restricted_data else None
-
-        await self.update_restricted_data(user_id)
-
-        out = await self.cache_provider.get_element(
-            get_element_id(collection_string, id), user_id
-        )
-        return json.loads(out.decode()) if out else None
+        return (changed_elements, deleted_elements)
 
     async def get_current_change_id(self) -> int:
         """
         Returns the current change id.
 
-        Returns start_time if there is no change id yet.
+        Returns default_change_id if there is no change id yet.
         """
         value = await self.cache_provider.get_current_change_id()
-        if not value:
-            return self.start_time
-        # Return the score (second element) of the first (and only) element
-        return value[0][1]
+        return value if value is not None else self.default_change_id
 
     async def get_lowest_change_id(self) -> int:
         """
@@ -479,7 +347,7 @@ class ElementCache:
         return value
 
 
-def load_element_cache(restricted_data: bool = True) -> ElementCache:
+def load_element_cache() -> ElementCache:
     """
     Generates an element cache instance.
     """
@@ -488,12 +356,8 @@ def load_element_cache(restricted_data: bool = True) -> ElementCache:
     else:
         cache_provider_class = MemmoryCacheProvider
 
-    return ElementCache(
-        cache_provider_class=cache_provider_class,
-        use_restricted_data_cache=restricted_data,
-    )
+    return ElementCache(cache_provider_class=cache_provider_class)
 
 
 # Set the element_cache
-use_restricted_data = getattr(settings, "RESTRICTED_DATA_CACHE", True)
-element_cache = load_element_cache(restricted_data=use_restricted_data)
+element_cache = load_element_cache()
diff --git a/openslides/utils/cache_providers.py b/openslides/utils/cache_providers.py
index 302293799..18b4ae666 100644
--- a/openslides/utils/cache_providers.py
+++ b/openslides/utils/cache_providers.py
@@ -1,17 +1,28 @@
+import functools
+import hashlib
+import logging
 from collections import defaultdict
-from typing import Any, Dict, Iterable, List, Optional, Set, Tuple
+from textwrap import dedent
+from typing import Any, Callable, Coroutine, Dict, List, Optional, Set, Tuple
 
-from django.apps import apps
+from django.core.exceptions import ImproperlyConfigured
 from typing_extensions import Protocol
 
 from .redis import use_redis
+from .schema_version import SchemaVersion
 from .utils import split_element_id, str_dict_to_bytes
 
 
+logger = logging.getLogger(__name__)
+
 if use_redis:
     from .redis import get_connection, aioredis
 
 
+class CacheReset(Exception):
+    pass
+
+
 class ElementCacheProvider(Protocol):
     """
     Base class for cache provider.
@@ -19,49 +30,43 @@ class ElementCacheProvider(Protocol):
     See RedisCacheProvider as reverence implementation.
     """
 
+    def __init__(self, ensure_cache: Callable[[], Coroutine[Any, Any, None]]) -> None:
+        ...
+
+    async def ensure_cache(self) -> None:
+        ...
+
     async def clear_cache(self) -> None:
         ...
 
     async def reset_full_cache(self, data: Dict[str, str]) -> None:
         ...
 
-    async def data_exists(self, user_id: Optional[int] = None) -> bool:
+    async def data_exists(self) -> bool:
         ...
 
-    async def add_elements(self, elements: List[str]) -> None:
+    async def get_all_data(self) -> Dict[bytes, bytes]:
         ...
 
-    async def del_elements(
-        self, elements: List[str], user_id: Optional[int] = None
-    ) -> None:
+    async def get_collection_data(self, collection: str) -> Dict[int, bytes]:
+        ...
+
+    async def get_element_data(self, element_id: str) -> Optional[bytes]:
         ...
 
     async def add_changed_elements(
-        self, default_change_id: int, element_ids: Iterable[str]
+        self,
+        changed_elements: List[str],
+        deleted_element_ids: List[str],
+        default_change_id: int,
     ) -> int:
         ...
 
-    async def get_all_data(self, user_id: Optional[int] = None) -> Dict[bytes, bytes]:
-        ...
-
-    async def get_collection_data(
-        self, collection: str, user_id: Optional[int] = None
-    ) -> Dict[bytes, bytes]:
-        ...
-
     async def get_data_since(
-        self, change_id: int, user_id: Optional[int] = None, max_change_id: int = -1
+        self, change_id: int, max_change_id: int = -1
     ) -> Tuple[Dict[str, List[bytes]], List[str]]:
         ...
 
-    async def get_element(
-        self, element_id: str, user_id: Optional[int] = None
-    ) -> Optional[bytes]:
-        ...
-
-    async def del_restricted_data(self, user_id: int) -> None:
-        ...
-
     async def set_lock(self, lock_name: str) -> bool:
         ...
 
@@ -71,18 +76,48 @@ class ElementCacheProvider(Protocol):
     async def del_lock(self, lock_name: str) -> None:
         ...
 
-    async def get_change_id_user(self, user_id: int) -> Optional[int]:
-        ...
-
-    async def update_restricted_data(self, user_id: int, data: Dict[str, str]) -> None:
-        ...
-
-    async def get_current_change_id(self) -> List[Tuple[str, int]]:
+    async def get_current_change_id(self) -> Optional[int]:
         ...
 
     async def get_lowest_change_id(self) -> Optional[int]:
         ...
 
+    async def get_schema_version(self) -> Optional[SchemaVersion]:
+        ...
+
+    async def set_schema_version(self, schema_version: SchemaVersion) -> None:
+        ...
+
+
+def ensure_cache_wrapper() -> Callable[[Callable[..., Any]], Callable[..., Any]]:
+    """
+    Wraps a cache function to ensure, that the cache is filled.
+    When the function raises a CacheReset-Error the cache will be ensured (call
+    to `ensure_cache`) and the method will be recalled. This is done, until the
+    operation was successful.
+    """
+
+    def wrapper(func: Callable[..., Any]) -> Callable[..., Any]:
+        @functools.wraps(func)
+        async def wrapped(
+            cache_provider: ElementCacheProvider, *args: Any, **kwargs: Any
+        ) -> Any:
+            success = False
+            while not success:
+                try:
+                    result = await func(cache_provider, *args, **kwargs)
+                    success = True
+                except CacheReset:
+                    logger.warn(
+                        f"Redis was flushed before method '{func.__name__}'. Ensures cache now."
+                    )
+                    await cache_provider.ensure_cache()
+            return result
+
+        return wrapped
+
+    return wrapper
+
 
 class RedisCacheProvider:
     """
@@ -90,204 +125,251 @@ class RedisCacheProvider:
     """
 
     full_data_cache_key: str = "full_data"
-    restricted_user_cache_key: str = "restricted_data:{user_id}"
     change_id_cache_key: str = "change_id"
+    schema_cache_key: str = "schema"
     prefix: str = "element_cache_"
 
+    # All lua-scripts used by this provider. Every entry is a Tuple (str, bool) with the
+    # script and an ensure_cache-indicator. If the indicator is True, a short ensure_cache-script
+    # will be prepended to the script which raises a CacheReset, if the full data cache is empty.
+    # This requires the full_data_cache_key to be the first key given in `keys`!
+    # All scripts are dedented and hashed for faster execution. Convention: The keys of this
+    # member are the methods that needs these scripts.
+    scripts = {
+        "clear_cache": (
+            "return redis.call('del', 'fake_key', unpack(redis.call('keys', ARGV[1])))",
+            False,
+        ),
+        "get_all_data": ("return redis.call('hgetall', KEYS[1])", True),
+        "get_collection_data": (
+            """
+            local cursor = 0
+            local collection = {}
+            repeat
+                local result = redis.call('HSCAN', KEYS[1], cursor, 'MATCH', ARGV[1])
+                cursor = tonumber(result[1])
+                for _, v in pairs(result[2]) do
+                    table.insert(collection, v)
+                end
+            until cursor == 0
+            return collection
+            """,
+            True,
+        ),
+        "get_element_data": ("return redis.call('hget', KEYS[1], ARGV[1])", True),
+        "add_changed_elements": (
+            """
+            -- Generate a new change_id
+            local tmp = redis.call('zrevrangebyscore', KEYS[2], '+inf', '-inf', 'WITHSCORES', 'LIMIT', 0, 1)
+            local change_id
+            if next(tmp) == nil then
+                -- The key does not exist
+                change_id = ARGV[1]
+            else
+                change_id = tmp[2] + 1
+            end
+
+            local nc = tonumber(ARGV[2])
+            local nd = tonumber(ARGV[3])
+
+            local i, max
+            -- Add changed_elements to the cache and sorted set (the first of the pairs)
+            if (nc > 0) then
+                max = 2 + nc
+                redis.call('hmset', KEYS[1], unpack(ARGV, 4, max + 1))
+                for i = 4, max, 2 do
+                    redis.call('zadd', KEYS[2], change_id, ARGV[i])
+                end
+            end
+
+            -- Delete deleted_element_ids and add them to sorted set
+            if (nd > 0) then
+                max = 3 + nc + nd
+                redis.call('hdel', KEYS[1], unpack(ARGV, 4 + nc, max))
+                for i = 4 + nc, max, 2 do
+                    redis.call('zadd', KEYS[2], change_id, ARGV[i])
+                end
+            end
+
+            -- Set lowest_change_id if it does not exist
+            redis.call('zadd', KEYS[2], 'NX', change_id, '_config:lowest_change_id')
+
+            return change_id
+            """,
+            True,
+        ),
+        "get_data_since": (
+            """
+            -- Get change ids of changed elements
+            local element_ids = redis.call('zrangebyscore', KEYS[2], ARGV[1], ARGV[2])
+
+            -- Save elements in array. Rotate element_id and element_json
+            local elements = {}
+            for _, element_id in pairs(element_ids) do
+              table.insert(elements, element_id)
+              table.insert(elements, redis.call('hget', KEYS[1], element_id))
+            end
+            return elements
+            """,
+            True,
+        ),
+    }
+
+    def __init__(self, ensure_cache: Callable[[], Coroutine[Any, Any, None]]) -> None:
+        self._ensure_cache = ensure_cache
+
+        # hash all scripts and remove indentation.
+        for key in self.scripts.keys():
+            script, add_ensure_cache = self.scripts[key]
+            script = dedent(script)
+            if add_ensure_cache:
+                script = (
+                    dedent(
+                        """
+                        local exist = redis.call('exists', KEYS[1])
+                        if (exist == 0) then
+                            redis.log(redis.LOG_WARNING, "empty: "..KEYS[1])
+                            return redis.error_reply("cache_reset")
+                        end
+                        """
+                    )
+                    + script
+                )
+            self.scripts[key] = (script, add_ensure_cache)
+        self._script_hashes = {
+            key: hashlib.sha1(script.encode()).hexdigest()
+            for key, (script, _) in self.scripts.items()
+        }
+
+    async def ensure_cache(self) -> None:
+        await self._ensure_cache()
+
     def get_full_data_cache_key(self) -> str:
         return "".join((self.prefix, self.full_data_cache_key))
 
-    def get_restricted_data_cache_key(self, user_id: int) -> str:
-        return "".join(
-            (self.prefix, self.restricted_user_cache_key.format(user_id=user_id))
-        )
-
     def get_change_id_cache_key(self) -> str:
         return "".join((self.prefix, self.change_id_cache_key))
 
+    def get_schema_cache_key(self) -> str:
+        return "".join((self.prefix, self.schema_cache_key))
+
     async def clear_cache(self) -> None:
         """
         Deleted all cache entries created with this element cache.
         """
-        async with get_connection() as redis:
-            await redis.eval(
-                "return redis.call('del', 'fake_key', unpack(redis.call('keys', ARGV[1])))",
-                keys=[],
-                args=[f"{self.prefix}*"],
-            )
+        await self.eval("clear_cache", keys=[], args=[f"{self.prefix}*"])
 
     async def reset_full_cache(self, data: Dict[str, str]) -> None:
         """
-        Deletes the full_data_cache and write new data in it.
-
-        Also deletes the restricted_data_cache and the change_id_cache.
+        Deletes the full_data_cache and write new data in it. Clears the change id key.
+        Does not clear locks.
         """
         async with get_connection() as redis:
             tr = redis.multi_exec()
-            # like clear_cache but does not delete a lock
-            tr.eval(
-                "return redis.call('del', 'fake_key', unpack(redis.call('keys', ARGV[1])))",
-                keys=[],
-                args=[f"{self.prefix}{self.restricted_user_cache_key}*"],
-            )
             tr.delete(self.get_change_id_cache_key())
             tr.delete(self.get_full_data_cache_key())
             tr.hmset_dict(self.get_full_data_cache_key(), data)
             await tr.execute()
 
-    async def data_exists(self, user_id: Optional[int] = None) -> bool:
+    async def data_exists(self) -> bool:
         """
         Returns True, when there is data in the cache.
-
-        If user_id is None, the method tests for full_data. If user_id is an int, it tests
-        for the restricted_data_cache for the user with the user_id. 0 is for anonymous.
         """
         async with get_connection() as redis:
-            if user_id is None:
-                cache_key = self.get_full_data_cache_key()
-            else:
-                cache_key = self.get_restricted_data_cache_key(user_id)
-            return await redis.exists(cache_key)
+            return await redis.exists(self.get_full_data_cache_key())
 
-    async def add_elements(self, elements: List[str]) -> None:
+    @ensure_cache_wrapper()
+    async def get_all_data(self) -> Dict[bytes, bytes]:
         """
-        Add or change elements to the cache.
-
-        elements is a list with an even len. the odd values are the element_ids and the even
-        values are the elements. The elements have to be encoded, for example with json.
+        Returns all data from the full_data_cache in a mapping from element_id to the element.
         """
-        async with get_connection() as redis:
-            await redis.hmset(self.get_full_data_cache_key(), *elements)
+        return await aioredis.util.wait_make_dict(
+            self.eval("get_all_data", [self.get_full_data_cache_key()])
+        )
 
-    async def del_elements(
-        self, elements: List[str], user_id: Optional[int] = None
-    ) -> None:
+    @ensure_cache_wrapper()
+    async def get_collection_data(self, collection: str) -> Dict[int, bytes]:
         """
-        Deletes elements from the cache.
-
-        elements has to be a list of element_ids.
-
-        If user_id is None, the elements are deleted from the full_data cache. If user_id is an
-        int, the elements are deleted one restricted_data_cache. 0 is for anonymous.
+        Returns all elements for a collection from the cache. The data is mapped
+        from element_id to the element.
         """
-        async with get_connection() as redis:
-            if user_id is None:
-                cache_key = self.get_full_data_cache_key()
-            else:
-                cache_key = self.get_restricted_data_cache_key(user_id)
-            await redis.hdel(cache_key, *elements)
+        response = await self.eval(
+            "get_collection_data", [self.get_full_data_cache_key()], [f"{collection}:*"]
+        )
 
+        collection_data = {}
+        for i in range(0, len(response), 2):
+            _, id = split_element_id(response[i])
+            collection_data[id] = response[i + 1]
+
+        return collection_data
+
+    @ensure_cache_wrapper()
+    async def get_element_data(self, element_id: str) -> Optional[bytes]:
+        """
+        Returns one element from the cache. Returns None, when the element does not exist.
+        """
+        try:
+            return await self.eval(
+                "get_element_data", [self.get_full_data_cache_key()], [element_id]
+            )
+        except aioredis.errors.ReplyError:
+            raise CacheReset()
+
+    @ensure_cache_wrapper()
     async def add_changed_elements(
-        self, default_change_id: int, element_ids: Iterable[str]
+        self,
+        changed_elements: List[str],
+        deleted_element_ids: List[str],
+        default_change_id: int,
     ) -> int:
         """
-        Saves which elements are change with a change_id.
-
-        Generates and returns the change_id.
+        Modified the full_data_cache to insert the changed_elements and removes the
+        deleted_element_ids (in this order). Generates a new change_id and inserts all
+        element_ids (changed and deleted) with the change_id into the change_id_cache.
+        The newly generated change_id is returned.
         """
-        async with get_connection() as redis:
-            return int(
-                await redis.eval(
-                    lua_script_change_data,
-                    keys=[self.get_change_id_cache_key()],
-                    args=[default_change_id, *element_ids],
-                )
+        return int(
+            await self.eval(
+                "add_changed_elements",
+                keys=[self.get_full_data_cache_key(), self.get_change_id_cache_key()],
+                args=[
+                    default_change_id,
+                    len(changed_elements),
+                    len(deleted_element_ids),
+                    *(changed_elements + deleted_element_ids),
+                ],
             )
+        )
 
-    async def get_all_data(self, user_id: Optional[int] = None) -> Dict[bytes, bytes]:
-        """
-        Returns all data from a cache.
-
-        if user_id is None, then the data is returned from the full_data_cache. If it is and
-        int, it is returned from a restricted_data_cache. 0 is for anonymous.
-        """
-        if user_id is None:
-            cache_key = self.get_full_data_cache_key()
-        else:
-            cache_key = self.get_restricted_data_cache_key(user_id)
-
-        async with get_connection() as redis:
-            return await redis.hgetall(cache_key)
-
-    async def get_collection_data(
-        self, collection: str, user_id: Optional[int] = None
-    ) -> Dict[bytes, bytes]:
-        """
-        Returns all elements for a collection from the cache.
-        """
-        if user_id is None:
-            cache_key = self.get_full_data_cache_key()
-        else:
-            cache_key = self.get_restricted_data_cache_key(user_id)
-
-        async with get_connection() as redis:
-            out = {}
-            async for k, v in redis.ihscan(cache_key, match=f"{collection}:*"):
-                out[k] = v
-            return out
-
-    async def get_element(
-        self, element_id: str, user_id: Optional[int] = None
-    ) -> Optional[bytes]:
-        """
-        Returns one element from the cache.
-
-        Returns None, when the element does not exist.
-        """
-        if user_id is None:
-            cache_key = self.get_full_data_cache_key()
-        else:
-            cache_key = self.get_restricted_data_cache_key(user_id)
-
-        async with get_connection() as redis:
-            return await redis.hget(cache_key, element_id)
-
+    @ensure_cache_wrapper()
     async def get_data_since(
-        self, change_id: int, user_id: Optional[int] = None, max_change_id: int = -1
+        self, change_id: int, max_change_id: int = -1
     ) -> Tuple[Dict[str, List[bytes]], List[str]]:
         """
-        Returns all elements since a change_id.
+        Returns all elements since a change_id (included) and until the max_change_id (included).
 
         The returend value is a two element tuple. The first value is a dict the elements where
         the key is the collection_string and the value a list of (json-) encoded elements. The
         second element is a list of element_ids, that have been deleted since the change_id.
-
-        if user_id is None, the full_data is returned. If user_id is an int, the restricted_data
-        for an user is used. 0 is for the anonymous user.
         """
         changed_elements: Dict[str, List[bytes]] = defaultdict(list)
         deleted_elements: List[str] = []
-        if user_id is None:
-            cache_key = self.get_full_data_cache_key()
-        else:
-            cache_key = self.get_restricted_data_cache_key(user_id)
 
         # Convert max_change_id to a string. If its negative, use the string '+inf'
         redis_max_change_id = "+inf" if max_change_id < 0 else str(max_change_id)
-        async with get_connection() as redis:
-            # lua script that returns gets all element_ids from change_id_cache_key
-            # and then uses each element_id on full_data or restricted_data.
-            # It returns a list where the odd values are the change_id and the
-            # even values the element as json. The function wait_make_dict creates
-            # a python dict from the returned list.
-            elements: Dict[bytes, Optional[bytes]] = await aioredis.util.wait_make_dict(
-                redis.eval(
-                    """
-                -- Get change ids of changed elements
-                local element_ids = redis.call('zrangebyscore', KEYS[1], ARGV[1], ARGV[2])
-
-                -- Save elements in array. Rotate element_id and element_json
-                local elements = {}
-                for _, element_id in pairs(element_ids) do
-                  table.insert(elements, element_id)
-                  table.insert(elements, redis.call('hget', KEYS[2], element_id))
-                end
-                return elements
-                """,
-                    keys=[self.get_change_id_cache_key(), cache_key],
-                    args=[change_id, redis_max_change_id],
-                )
+        # lua script that returns gets all element_ids from change_id_cache_key
+        # and then uses each element_id on full_data or restricted_data.
+        # It returns a list where the odd values are the change_id and the
+        # even values the element as json. The function wait_make_dict creates
+        # a python dict from the returned list.
+        elements: Dict[bytes, Optional[bytes]] = await aioredis.util.wait_make_dict(
+            self.eval(
+                "get_data_since",
+                keys=[self.get_full_data_cache_key(), self.get_change_id_cache_key()],
+                args=[change_id, redis_max_change_id],
             )
+        )
 
         for element_id, element_json in elements.items():
             if element_id.startswith(b"_config"):
@@ -301,20 +383,11 @@ class RedisCacheProvider:
                 changed_elements[collection_string].append(element_json)
         return changed_elements, deleted_elements
 
-    async def del_restricted_data(self, user_id: int) -> None:
-        """
-        Deletes all restricted_data for an user. 0 is for the anonymous user.
-        """
-        async with get_connection() as redis:
-            await redis.delete(self.get_restricted_data_cache_key(user_id))
-
     async def set_lock(self, lock_name: str) -> bool:
         """
         Tries to sets a lock.
 
-        Returns True when the lock could be set.
-
-        Returns False when the lock was already set.
+        Returns True when the lock could be set and False, if it was already set.
         """
         # TODO: Improve lock. See: https://redis.io/topics/distlock
         async with get_connection() as redis:
@@ -322,48 +395,28 @@ class RedisCacheProvider:
 
     async def get_lock(self, lock_name: str) -> bool:
         """
-        Returns True, when the lock for the restricted_data of an user is set. Else False.
+        Returns True, when the lock is set. Else False.
         """
         async with get_connection() as redis:
             return await redis.get(f"{self.prefix}lock_{lock_name}")
 
     async def del_lock(self, lock_name: str) -> None:
         """
-        Deletes the lock for the restricted_data of an user. Does nothing when the
-        lock is not set.
+        Deletes the lock. Does nothing when the lock is not set.
         """
         async with get_connection() as redis:
             await redis.delete(f"{self.prefix}lock_{lock_name}")
 
-    async def get_change_id_user(self, user_id: int) -> Optional[int]:
-        """
-        Get the change_id for the restricted_data of an user.
-
-        This is the change_id where the restricted_data was last calculated.
-        """
-        async with get_connection() as redis:
-            return await redis.hget(
-                self.get_restricted_data_cache_key(user_id), "_config:change_id"
-            )
-
-    async def update_restricted_data(self, user_id: int, data: Dict[str, str]) -> None:
-        """
-        Updates the restricted_data for an user.
-
-        data has to be a dict where the key is an element_id and the value the (json-) encoded
-        element.
-        """
-        async with get_connection() as redis:
-            await redis.hmset_dict(self.get_restricted_data_cache_key(user_id), data)
-
-    async def get_current_change_id(self) -> List[Tuple[str, int]]:
+    async def get_current_change_id(self) -> Optional[int]:
         """
         Get the highest change_id from redis.
         """
         async with get_connection() as redis:
-            return await redis.zrevrangebyscore(
+            value = await redis.zrevrangebyscore(
                 self.get_change_id_cache_key(), withscores=True, count=1, offset=0
             )
+            # Return the score (second element) of the first (and only) element, if exists.
+            return value[0][1] if value else None
 
     async def get_lowest_change_id(self) -> Optional[int]:
         """
@@ -376,6 +429,53 @@ class RedisCacheProvider:
                 self.get_change_id_cache_key(), "_config:lowest_change_id"
             )
 
+    async def get_schema_version(self) -> Optional[SchemaVersion]:
+        """ Retrieves the schema version of the cache or None, if not existent """
+        async with get_connection() as redis:
+            schema_version = await redis.hgetall(self.get_schema_cache_key())
+        if not schema_version:
+            return None
+
+        return {
+            "migration": int(schema_version[b"migration"].decode()),
+            "config": int(schema_version[b"config"].decode()),
+            "db": schema_version[b"db"].decode(),
+        }
+
+    async def set_schema_version(self, schema_version: SchemaVersion) -> None:
+        """ Sets the schema version for this cache. """
+        async with get_connection() as redis:
+            await redis.hmset_dict(self.get_schema_cache_key(), schema_version)
+
+    async def eval(
+        self, script_name: str, keys: List[str] = [], args: List[Any] = []
+    ) -> Any:
+        """
+        Runs a lua script in redis. This wrapper around redis.eval tries to make
+        usage of redis script cache. First the hash is send to the server and if
+        the script is not present there (NOSCRIPT error) the actual script will be
+        send.
+        If the script uses the ensure_cache-prefix, the first key must be the full_data
+        cache key. This is checked here.
+        """
+        hash = self._script_hashes[script_name]
+        if (
+            self.scripts[script_name][1]
+            and not keys[0] == self.get_full_data_cache_key()
+        ):
+            raise ImproperlyConfigured(
+                "A script with a ensure_cache prefix must have the full_data cache key as its first key"
+            )
+
+        async with get_connection() as redis:
+            try:
+                return await redis.evalsha(hash, keys, args)
+            except aioredis.errors.ReplyError as e:
+                if str(e).startswith("NOSCRIPT"):
+                    return await redis.eval(self.scripts[script_name][0], keys, args)
+                else:
+                    raise e
+
 
 class MemmoryCacheProvider:
     """
@@ -385,112 +485,86 @@ class MemmoryCacheProvider:
 
     This provider supports only one process. It saves the data into the memory.
     When you use different processes they will use diffrent data.
+
+    For this reason, the ensure_cache is not used and the schema version always
+    returns an invalid schema to always buold the cache.
     """
 
-    def __init__(self) -> None:
+    def __init__(self, ensure_cache: Callable[[], Coroutine[Any, Any, None]]) -> None:
         self.set_data_dicts()
 
     def set_data_dicts(self) -> None:
         self.full_data: Dict[str, str] = {}
-        self.restricted_data: Dict[int, Dict[str, str]] = {}
         self.change_id_data: Dict[int, Set[str]] = {}
         self.locks: Dict[str, str] = {}
 
+    async def ensure_cache(self) -> None:
+        pass
+
     async def clear_cache(self) -> None:
         self.set_data_dicts()
 
     async def reset_full_cache(self, data: Dict[str, str]) -> None:
+        self.change_id_data = {}
         self.full_data = data
 
-    async def data_exists(self, user_id: Optional[int] = None) -> bool:
-        if user_id is None:
-            cache_dict = self.full_data
-        else:
-            cache_dict = self.restricted_data.get(user_id, {})
+    async def data_exists(self) -> bool:
+        return bool(self.full_data)
 
-        return bool(cache_dict)
+    async def get_all_data(self) -> Dict[bytes, bytes]:
+        return str_dict_to_bytes(self.full_data)
 
-    async def add_elements(self, elements: List[str]) -> None:
-        if len(elements) % 2:
-            raise ValueError(
-                "The argument elements of add_elements has to be a list with an even number of elements."
-            )
+    async def get_collection_data(self, collection: str) -> Dict[int, bytes]:
+        out = {}
+        query = f"{collection}:"
+        for element_id, value in self.full_data.items():
+            if element_id.startswith(query):
+                _, id = split_element_id(element_id)
+                out[id] = value.encode()
+        return out
 
-        for i in range(0, len(elements), 2):
-            self.full_data[elements[i]] = elements[i + 1]
-
-    async def del_elements(
-        self, elements: List[str], user_id: Optional[int] = None
-    ) -> None:
-        if user_id is None:
-            cache_dict = self.full_data
-        else:
-            cache_dict = self.restricted_data.get(user_id, {})
-
-        for element in elements:
-            try:
-                del cache_dict[element]
-            except KeyError:
-                pass
+    async def get_element_data(self, element_id: str) -> Optional[bytes]:
+        value = self.full_data.get(element_id, None)
+        return value.encode() if value is not None else None
 
     async def add_changed_elements(
-        self, default_change_id: int, element_ids: Iterable[str]
+        self,
+        changed_elements: List[str],
+        deleted_element_ids: List[str],
+        default_change_id: int,
     ) -> int:
-        element_ids = list(element_ids)
-        try:
-            change_id = (await self.get_current_change_id())[0][1] + 1
-        except IndexError:
+        current_change_id = await self.get_current_change_id()
+        if current_change_id is None:
             change_id = default_change_id
+        else:
+            change_id = current_change_id + 1
+
+        for i in range(0, len(changed_elements), 2):
+            element_id = changed_elements[i]
+            self.full_data[element_id] = changed_elements[i + 1]
 
-        for element_id in element_ids:
             if change_id in self.change_id_data:
                 self.change_id_data[change_id].add(element_id)
             else:
                 self.change_id_data[change_id] = {element_id}
+
+        for element_id in deleted_element_ids:
+            try:
+                del self.full_data[element_id]
+            except KeyError:
+                pass
+            if change_id in self.change_id_data:
+                self.change_id_data[change_id].add(element_id)
+            else:
+                self.change_id_data[change_id] = {element_id}
+
         return change_id
 
-    async def get_all_data(self, user_id: Optional[int] = None) -> Dict[bytes, bytes]:
-        if user_id is None:
-            cache_dict = self.full_data
-        else:
-            cache_dict = self.restricted_data.get(user_id, {})
-
-        return str_dict_to_bytes(cache_dict)
-
-    async def get_collection_data(
-        self, collection: str, user_id: Optional[int] = None
-    ) -> Dict[bytes, bytes]:
-        if user_id is None:
-            cache_dict = self.full_data
-        else:
-            cache_dict = self.restricted_data.get(user_id, {})
-
-        out = {}
-        for key, value in cache_dict.items():
-            if key.startswith(f"{collection}:"):
-                out[key] = value
-        return str_dict_to_bytes(out)
-
-    async def get_element(
-        self, element_id: str, user_id: Optional[int] = None
-    ) -> Optional[bytes]:
-        if user_id is None:
-            cache_dict = self.full_data
-        else:
-            cache_dict = self.restricted_data.get(user_id, {})
-
-        value = cache_dict.get(element_id, None)
-        return value.encode() if value is not None else None
-
     async def get_data_since(
-        self, change_id: int, user_id: Optional[int] = None, max_change_id: int = -1
+        self, change_id: int, max_change_id: int = -1
     ) -> Tuple[Dict[str, List[bytes]], List[str]]:
         changed_elements: Dict[str, List[bytes]] = defaultdict(list)
         deleted_elements: List[str] = []
-        if user_id is None:
-            cache_dict = self.full_data
-        else:
-            cache_dict = self.restricted_data.get(user_id, {})
 
         all_element_ids: Set[str] = set()
         for data_change_id, element_ids in self.change_id_data.items():
@@ -500,7 +574,7 @@ class MemmoryCacheProvider:
                 all_element_ids.update(element_ids)
 
         for element_id in all_element_ids:
-            element_json = cache_dict.get(element_id, None)
+            element_json = self.full_data.get(element_id, None)
             if element_json is None:
                 deleted_elements.append(element_id)
             else:
@@ -508,12 +582,6 @@ class MemmoryCacheProvider:
                 changed_elements[collection_string].append(element_json.encode())
         return changed_elements, deleted_elements
 
-    async def del_restricted_data(self, user_id: int) -> None:
-        try:
-            del self.restricted_data[user_id]
-        except KeyError:
-            pass
-
     async def set_lock(self, lock_name: str) -> bool:
         if lock_name in self.locks:
             return False
@@ -529,20 +597,11 @@ class MemmoryCacheProvider:
         except KeyError:
             pass
 
-    async def get_change_id_user(self, user_id: int) -> Optional[int]:
-        data = self.restricted_data.get(user_id, {})
-        change_id = data.get("_config:change_id", None)
-        return int(change_id) if change_id is not None else None
-
-    async def update_restricted_data(self, user_id: int, data: Dict[str, str]) -> None:
-        redis_data = self.restricted_data.setdefault(user_id, {})
-        redis_data.update(data)
-
-    async def get_current_change_id(self) -> List[Tuple[str, int]]:
+    async def get_current_change_id(self) -> Optional[int]:
         change_data = self.change_id_data
         if change_data:
-            return [("no_usefull_value", max(change_data.keys()))]
-        return []
+            return max(change_data.keys())
+        return None
 
     async def get_lowest_change_id(self) -> Optional[int]:
         change_data = self.change_id_data
@@ -550,6 +609,12 @@ class MemmoryCacheProvider:
             return min(change_data.keys())
         return None
 
+    async def get_schema_version(self) -> Optional[SchemaVersion]:
+        return None
+
+    async def set_schema_version(self, schema_version: SchemaVersion) -> None:
+        pass
+
 
 class Cachable(Protocol):
     """
@@ -577,45 +642,3 @@ class Cachable(Protocol):
         elements can be an empty list, a list with some elements of the cachable or with all
         elements of the cachable.
         """
-
-
-def get_all_cachables() -> List[Cachable]:
-    """
-    Returns all element of OpenSlides.
-    """
-    out: List[Cachable] = []
-    for app in apps.get_app_configs():
-        try:
-            # Get the method get_startup_elements() from an app.
-            # This method has to return an iterable of Cachable objects.
-            get_startup_elements = app.get_startup_elements
-        except AttributeError:
-            # Skip apps that do not implement get_startup_elements.
-            continue
-        out.extend(get_startup_elements())
-    return out
-
-
-lua_script_change_data = """
--- Generate a new change_id
-local tmp = redis.call('zrevrangebyscore', KEYS[1], '+inf', '-inf', 'WITHSCORES', 'LIMIT', 0, 1)
-local change_id
-if next(tmp) == nil then
-    -- The key does not exist
-    change_id = ARGV[1]
-else
-    change_id = tmp[2] + 1
-end
-
--- Add elements to sorted set
-local count = 2
-while ARGV[count] do
-    redis.call('zadd', KEYS[1], change_id, ARGV[count])
-    count = count + 1
-end
-
--- Set lowest_change_id if it does not exist
-redis.call('zadd', KEYS[1], 'NX', change_id, '_config:lowest_change_id')
-
-return change_id
-"""
diff --git a/openslides/utils/consumers.py b/openslides/utils/consumers.py
index c54b3574a..690e9e74b 100644
--- a/openslides/utils/consumers.py
+++ b/openslides/utils/consumers.py
@@ -1,14 +1,15 @@
 import logging
 import time
 from collections import defaultdict
-from typing import Any, Dict, List
+from typing import Any, Dict, List, Optional
 from urllib.parse import parse_qs
 
+from ..utils.websocket import WEBSOCKET_CHANGE_ID_TOO_HIGH
 from .auth import async_anonymous_is_enabled
 from .autoupdate import AutoupdateFormat
 from .cache import element_cache, split_element_id
 from .utils import get_worker_id
-from .websocket import ProtocollAsyncJsonWebsocketConsumer, get_element_data
+from .websocket import ProtocollAsyncJsonWebsocketConsumer
 
 
 logger = logging.getLogger("openslides.websocket")
@@ -70,13 +71,7 @@ class SiteConsumer(ProtocollAsyncJsonWebsocketConsumer):
 
         if change_id is not None:
             logger.debug(f"connect: change id {change_id} ({self._id})")
-            try:
-                data = await get_element_data(self.scope["user"]["id"], change_id)
-            except ValueError:
-                # When the change_id is to big, do nothing
-                pass
-            else:
-                await self.send_json(type="autoupdate", content=data)
+            await self.send_autoupdate(change_id)
         else:
             logger.debug(f"connect: no change id ({self._id})")
 
@@ -111,30 +106,69 @@ class SiteConsumer(ProtocollAsyncJsonWebsocketConsumer):
             item["senderUserId"] = event["senderUserId"]
             await self.send_json(type="notify", content=item)
 
-    async def send_data(self, event: Dict[str, Any]) -> None:
+    async def send_autoupdate(
+        self,
+        change_id: int,
+        max_change_id: Optional[int] = None,
+        in_response: Optional[str] = None,
+    ) -> None:
         """
-        Send changed or deleted elements to the user.
+        Sends an autoupdate to the client from change_id to max_change_id.
+        If max_change_id is None, the current change id will be used.
         """
-        change_id = event["change_id"]
-        changed_elements, deleted_elements_ids = await element_cache.get_restricted_data(
-            self.scope["user"]["id"], change_id, max_change_id=change_id
-        )
+        user_id = self.scope["user"]["id"]
+
+        if max_change_id is None:
+            max_change_id = await element_cache.get_current_change_id()
+
+        if change_id == max_change_id + 1:
+            # The client is up-to-date, so nothing will be done
+            return
+
+        if change_id > max_change_id:
+            message = f"Requested change_id {change_id} is higher this highest change_id {max_change_id}."
+            await self.send_error(
+                code=WEBSOCKET_CHANGE_ID_TOO_HIGH,
+                message=message,
+                in_response=in_response,
+            )
+            return
+
+        try:
+            changed_elements, deleted_element_ids = await element_cache.get_data_since(
+                user_id, change_id, max_change_id
+            )
+        except RuntimeError:
+            # The change_id is lower the the lowerst change_id in redis. Return all data
+            changed_elements = await element_cache.get_all_data_list(user_id)
+            all_data = True
+            deleted_elements: Dict[str, List[int]] = {}
+        else:
+            all_data = False
+            deleted_elements = defaultdict(list)
+            for element_id in deleted_element_ids:
+                collection_string, id = split_element_id(element_id)
+                deleted_elements[collection_string].append(id)
 
-        deleted_elements: Dict[str, List[int]] = defaultdict(list)
-        for element_id in deleted_elements_ids:
-            collection_string, id = split_element_id(element_id)
-            deleted_elements[collection_string].append(id)
         await self.send_json(
             type="autoupdate",
             content=AutoupdateFormat(
                 changed=changed_elements,
                 deleted=deleted_elements,
                 from_change_id=change_id,
-                to_change_id=change_id,
-                all_data=False,
+                to_change_id=max_change_id,
+                all_data=all_data,
             ),
+            in_response=in_response,
         )
 
+    async def send_data(self, event: Dict[str, Any]) -> None:
+        """
+        Send changed or deleted elements to the user.
+        """
+        change_id = event["change_id"]
+        await self.send_autoupdate(change_id, max_change_id=change_id)
+
     async def projector_changed(self, event: Dict[str, Any]) -> None:
         """
         The projector has changed.
diff --git a/openslides/utils/middleware.py b/openslides/utils/middleware.py
index 79ac4cdb5..513755988 100644
--- a/openslides/utils/middleware.py
+++ b/openslides/utils/middleware.py
@@ -54,7 +54,7 @@ async def get_user(scope: Dict[str, Any]) -> Dict[str, Any]:
         pass
     else:
         if backend_path in settings.AUTHENTICATION_BACKENDS:
-            user = await element_cache.get_element_full_data("users/user", user_id)
+            user = await element_cache.get_element_data("users/user", user_id)
             if user:
                 # Verify the session
                 session_hash = session.get(HASH_SESSION_KEY)
diff --git a/openslides/utils/projector.py b/openslides/utils/projector.py
index 7a21df2a6..321dcc855 100644
--- a/openslides/utils/projector.py
+++ b/openslides/utils/projector.py
@@ -67,7 +67,7 @@ async def get_projector_data(
     if projector_ids is None:
         projector_ids = []
 
-    all_data = await element_cache.get_all_full_data_ordered()
+    all_data = await element_cache.get_all_data_dict()
     projector_data: Dict[int, List[Dict[str, Any]]] = {}
 
     for projector_id, projector in all_data.get("core/projector", {}).items():
diff --git a/openslides/utils/rest_api.py b/openslides/utils/rest_api.py
index b29f12a27..59edc07ae 100644
--- a/openslides/utils/rest_api.py
+++ b/openslides/utils/rest_api.py
@@ -253,10 +253,11 @@ class ListModelMixin(_ListModelMixin):
             # The corresponding queryset does not support caching.
             response = super().list(request, *args, **kwargs)
         else:
+            # TODO
             # This loads all data from the cache, not only the requested data.
             # If we would use the rest api, we should add a method
             # element_cache.get_collection_restricted_data
-            all_restricted_data = async_to_sync(element_cache.get_all_restricted_data)(
+            all_restricted_data = async_to_sync(element_cache.get_all_data_list)(
                 request.user.pk or 0
             )
             response = Response(all_restricted_data.get(collection_string, []))
@@ -278,8 +279,8 @@ class RetrieveModelMixin(_RetrieveModelMixin):
         else:
             lookup_url_kwarg = self.lookup_url_kwarg or self.lookup_field
             user_id = request.user.pk or 0
-            content = async_to_sync(element_cache.get_element_restricted_data)(
-                user_id, collection_string, self.kwargs[lookup_url_kwarg]
+            content = async_to_sync(element_cache.get_element_data)(
+                collection_string, self.kwargs[lookup_url_kwarg], user_id
             )
             if content is None:
                 raise Http404
diff --git a/openslides/utils/schema_version.py b/openslides/utils/schema_version.py
new file mode 100644
index 000000000..0fdab1461
--- /dev/null
+++ b/openslides/utils/schema_version.py
@@ -0,0 +1,84 @@
+import logging
+from typing import Optional
+
+from django.db.models import Max
+from mypy_extensions import TypedDict
+
+
+logger = logging.getLogger(__name__)
+SchemaVersion = TypedDict("SchemaVersion", {"migration": int, "config": int, "db": str})
+
+
+class SchemaVersionHandler:
+    """
+    Handler for the schema version of this running OpenSlides instance.
+    What is a schema version? This is an indictor of the current schema of the data
+    in the database, config variables, and the database itself. E.b. with a migration,
+    new/changed config variables or with a database change, the schema of the data changes.
+
+    To detect this is needed to reset the cache, so it does not hold any old data. This
+    affects the server cache, but also the client uses this technique to flush the cache.
+
+    Get the current schema with `get`. The schema version is built just once. After a change
+    in the schema, all workers needs a restart!
+    """
+
+    def __init__(self) -> None:
+        self._schema_version: Optional[SchemaVersion] = None
+
+    def get(self) -> SchemaVersion:
+        if self._schema_version is not None:
+            return self._schema_version
+
+        from django.db.migrations.recorder import MigrationRecorder
+
+        migration = MigrationRecorder.Migration.objects.aggregate(Max("id"))["id__max"]
+
+        from openslides.core.config import ConfigStore
+
+        try:
+            config = ConfigStore.objects.get(key="config_version").value
+        except ConfigStore.DoesNotExist:
+            config = 0
+        try:
+            db = ConfigStore.objects.get(key="db_id").value
+        except ConfigStore.DoesNotExist:
+            db = ""
+
+        self._schema_version = {"migration": migration, "config": config, "db": db}
+        return self._schema_version
+
+    def compare(self, other: Optional[SchemaVersion]) -> bool:
+        current = self.get()
+
+        if not other:
+            logger.info("No old schema version")
+            return False
+
+        equal = True
+        if current["db"] != other["db"]:
+            other_db = other["db"] or "<empty>"
+            logger.info(f"DB changed from {other_db} to {current['db']}")
+            equal = False
+        if current["config"] != other["config"]:
+            other_config = other["config"] or "<empty>"
+            logger.info(f"Config changed from {other_config} to {current['config']}")
+            equal = False
+        if current["migration"] != other["migration"]:
+            logger.info(
+                f"Migration changed from {other['migration']} to {current['migration']}"
+            )
+            equal = False
+        return equal
+
+    def log_current(self) -> None:
+        current = self.get()
+        logger.info(
+            f"""Schema version:
+    DB:        {current["db"]}
+    migration: {current["migration"]}
+    config:    {current["config"]}"""
+        )
+
+
+schema_version_handler = SchemaVersionHandler()
diff --git a/openslides/utils/settings.py.tpl b/openslides/utils/settings.py.tpl
index 39a6c44bf..8c55d260b 100644
--- a/openslides/utils/settings.py.tpl
+++ b/openslides/utils/settings.py.tpl
@@ -100,11 +100,6 @@ if use_redis:
     # or a unix domain socket path string — "/path/to/redis.sock".
     REDIS_ADDRESS = "redis://127.0.0.1"
 
-    # When use_redis is True, the restricted data cache caches the data individuel
-    # for each user. This requires a lot of memory if there are a lot of active
-    # users.
-    RESTRICTED_DATA_CACHE = True
-
     # Session backend
 
     # Redis configuration for django-redis-sessions.
diff --git a/openslides/utils/websocket.py b/openslides/utils/websocket.py
index b8d73cace..717726705 100644
--- a/openslides/utils/websocket.py
+++ b/openslides/utils/websocket.py
@@ -1,6 +1,5 @@
 import json
-from collections import defaultdict
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, Optional
 
 import jsonschema
 import lz4.frame
@@ -8,10 +7,7 @@ from channels.generic.websocket import AsyncWebsocketConsumer
 from django.conf import settings
 from websockets.exceptions import ConnectionClosed
 
-from .autoupdate import AutoupdateFormat
-from .cache import element_cache
 from .stats import WebsocketThroughputLogger
-from .utils import split_element_id
 
 
 # Custom Websocket error codes (not to be confused with the websocket *connection*
@@ -25,7 +21,7 @@ WEBSOCKET_CHANGE_ID_TOO_HIGH = 101
 # If data is requested and the given change id is higher than the highest change id
 # from the element_cache.
 
-WEBSOCKET_WRONG_FORMAT = 10
+WEBSOCKET_WRONG_FORMAT = 102
 # If the recieved data has not the expected format.
 
 
@@ -232,37 +228,3 @@ def register_client_message(
         message_schema["required"] = ["content"]
 
     schema["anyOf"].append(message_schema)
-
-
-async def get_element_data(user_id: int, change_id: int = 0) -> AutoupdateFormat:
-    """
-    Returns all element data since a change_id.
-    """
-    current_change_id = await element_cache.get_current_change_id()
-    if change_id > current_change_id:
-        raise ValueError(
-            f"Requested change_id {change_id} is higher this highest change_id {current_change_id}."
-        )
-    try:
-        changed_elements, deleted_element_ids = await element_cache.get_restricted_data(
-            user_id, change_id, current_change_id
-        )
-    except RuntimeError:
-        # The change_id is lower the the lowerst change_id in redis. Return all data
-        changed_elements = await element_cache.get_all_restricted_data(user_id)
-        all_data = True
-        deleted_elements: Dict[str, List[int]] = {}
-    else:
-        all_data = False
-        deleted_elements = defaultdict(list)
-        for element_id in deleted_element_ids:
-            collection_string, id = split_element_id(element_id)
-            deleted_elements[collection_string].append(id)
-
-    return AutoupdateFormat(
-        changed=changed_elements,
-        deleted=deleted_elements,
-        from_change_id=change_id,
-        to_change_id=current_change_id,
-        all_data=all_data,
-    )
diff --git a/tests/conftest.py b/tests/conftest.py
index 7cb15e490..ddd7ceb3a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -82,5 +82,5 @@ def reset_cache(request):
         async_to_sync(element_cache.cache_provider.clear_cache)()
         element_cache.ensure_cache(reset=True)
 
-    # Set constant start_time
-    element_cache.start_time = 1
+    # Set constant default change_id
+    element_cache.set_default_change_id(1)
diff --git a/tests/integration/utils/test_consumers.py b/tests/integration/utils/test_consumers.py
index f7d665124..09d66da63 100644
--- a/tests/integration/utils/test_consumers.py
+++ b/tests/integration/utils/test_consumers.py
@@ -16,7 +16,10 @@ from openslides.utils.autoupdate import (
     inform_deleted_data,
 )
 from openslides.utils.cache import element_cache
-from openslides.utils.websocket import WEBSOCKET_CHANGE_ID_TOO_HIGH
+from openslides.utils.websocket import (
+    WEBSOCKET_CHANGE_ID_TOO_HIGH,
+    WEBSOCKET_WRONG_FORMAT,
+)
 
 from ...unit.utils.cache_provider import Collection1, Collection2, get_cachable_provider
 from ..helpers import TConfig, TProjector, TUser
@@ -36,7 +39,7 @@ async def prepare_element_cache(settings):
         [Collection1(), Collection2(), TConfig(), TUser(), TProjector()]
     )
     element_cache._cachables = None
-    await sync_to_async(element_cache.ensure_cache)()
+    await element_cache.async_ensure_cache(default_change_id=1)
     yield
     # Reset the cachable_provider
     element_cache.cachable_provider = orig_cachable_provider
@@ -118,31 +121,6 @@ async def test_connection_with_change_id(get_communicator, set_config):
     assert TUser().get_collection_string() in content["changed"]
 
 
-@pytest.mark.asyncio
-async def test_connection_with_change_id_get_restricted_data_with_restricted_data_cache(
-    get_communicator, set_config
-):
-    """
-    Test, that the returned data is the restricted_data when restricted_data_cache is activated
-    """
-    try:
-        # Save the value of use_restricted_data_cache
-        original_use_restricted_data = element_cache.use_restricted_data_cache
-        element_cache.use_restricted_data_cache = True
-
-        await set_config("general_system_enable_anonymous", True)
-        communicator = get_communicator("change_id=0")
-        await communicator.connect()
-
-        response = await communicator.receive_json_from()
-
-        content = response.get("content")
-        assert content["changed"]["app/collection1"][0]["value"] == "restricted_value1"
-    finally:
-        # reset the value of use_restricted_data_cache
-        element_cache.use_restricted_data_cache = original_use_restricted_data
-
-
 @pytest.mark.xfail  # This will fail until a proper solution in #4009
 @pytest.mark.asyncio
 async def test_connection_with_invalid_change_id(get_communicator, set_config):
@@ -154,14 +132,14 @@ async def test_connection_with_invalid_change_id(get_communicator, set_config):
 
 
 @pytest.mark.asyncio
-async def test_connection_with_to_big_change_id(get_communicator, set_config):
+async def test_connection_with_too_big_change_id(get_communicator, set_config):
     await set_config("general_system_enable_anonymous", True)
     communicator = get_communicator("change_id=100")
 
     connected, __ = await communicator.connect()
 
     assert connected is True
-    assert await communicator.receive_nothing()
+    await communicator.assert_receive_error(code=WEBSOCKET_CHANGE_ID_TOO_HIGH)
 
 
 @pytest.mark.asyncio
@@ -271,8 +249,7 @@ async def test_invalid_websocket_message_type(communicator, set_config):
 
     await communicator.send_json_to([])
 
-    response = await communicator.receive_json_from()
-    assert response["type"] == "error"
+    await communicator.assert_receive_error(code=WEBSOCKET_WRONG_FORMAT)
 
 
 @pytest.mark.asyncio
@@ -282,8 +259,7 @@ async def test_invalid_websocket_message_no_id(communicator, set_config):
 
     await communicator.send_json_to({"type": "test", "content": "foobar"})
 
-    response = await communicator.receive_json_from()
-    assert response["type"] == "error"
+    await communicator.assert_receive_error(code=WEBSOCKET_WRONG_FORMAT)
 
 
 @pytest.mark.asyncio
@@ -299,9 +275,9 @@ async def test_send_unknown_type(communicator, set_config):
         }
     )
 
-    response = await communicator.receive_json_from()
-    assert response["type"] == "error"
-    assert response["in_response"] == "test_id"
+    await communicator.assert_receive_error(
+        code=WEBSOCKET_WRONG_FORMAT, in_response="test_id"
+    )
 
 
 @pytest.mark.asyncio
@@ -343,18 +319,16 @@ async def test_send_get_elements(communicator, set_config):
 
 
 @pytest.mark.asyncio
-async def test_send_get_elements_to_big_change_id(communicator, set_config):
+async def test_send_get_elements_too_big_change_id(communicator, set_config):
     await set_config("general_system_enable_anonymous", True)
     await communicator.connect()
 
     await communicator.send_json_to(
         {"type": "getElements", "content": {"change_id": 100}, "id": "test_id"}
     )
-    response = await communicator.receive_json_from()
-
-    type = response.get("type")
-    assert type == "error"
-    assert response.get("in_response") == "test_id"
+    await communicator.assert_receive_error(
+        code=WEBSOCKET_CHANGE_ID_TOO_HIGH, in_response="test_id"
+    )
 
 
 @pytest.mark.asyncio
@@ -374,10 +348,10 @@ async def test_send_get_elements_to_small_change_id(communicator, set_config):
 
 
 @pytest.mark.asyncio
-async def test_send_connect_twice_with_clear_change_id_cache(communicator, set_config):
+async def test_send_connect_up_to_date(communicator, set_config):
     """
-    Test, that a second request with change_id+1 from the first request, returns
-    an error.
+    Test, that a second request with change_id+1 from the first request does not
+    send anything, becuase the client is up to date.
     """
     await set_config("general_system_enable_anonymous", True)
     element_cache.cache_provider.change_id_data = {}  # type: ignore
@@ -395,13 +369,7 @@ async def test_send_connect_twice_with_clear_change_id_cache(communicator, set_c
             "id": "test_id",
         }
     )
-    response2 = await communicator.receive_json_from()
-
-    assert response2["type"] == "error"
-    assert response2.get("content") == {
-        "code": WEBSOCKET_CHANGE_ID_TOO_HIGH,
-        "message": "Requested change_id 2 is higher this highest change_id 1.",
-    }
+    assert await communicator.receive_nothing()
 
 
 @pytest.mark.xfail  # This test is broken
diff --git a/tests/integration/websocket.py b/tests/integration/websocket.py
index 7ff15a133..a528eeee9 100644
--- a/tests/integration/websocket.py
+++ b/tests/integration/websocket.py
@@ -23,3 +23,16 @@ class WebsocketCommunicator(ChannelsWebsocketCommunicator):
 
         assert isinstance(text_data, str), "JSON data is not a text frame"
         return json.loads(text_data)
+
+    async def assert_receive_error(self, timeout=1, in_response=None, **kwargs):
+        response = await self.receive_json_from(timeout)
+        assert response["type"] == "error"
+
+        content = response.get("content")
+        if kwargs:
+            assert content
+        for key, value in kwargs.items():
+            assert content.get(key) == value
+
+        if in_response:
+            assert response["in_response"] == in_response
diff --git a/tests/unit/utils/test_cache.py b/tests/unit/utils/test_cache.py
index 06f2d7060..59876c588 100644
--- a/tests/unit/utils/test_cache.py
+++ b/tests/unit/utils/test_cache.py
@@ -1,6 +1,5 @@
 import json
 from typing import Any, Dict, List
-from unittest.mock import patch
 
 import pytest
 
@@ -32,9 +31,10 @@ def element_cache():
     element_cache = ElementCache(
         cache_provider_class=TTestCacheProvider,
         cachable_provider=get_cachable_provider(),
-        start_time=0,
+        default_change_id=0,
     )
     element_cache.ensure_cache()
+    element_cache.set_default_change_id(0)
     return element_cache
 
 
@@ -44,7 +44,7 @@ async def test_change_elements(element_cache):
         "app/collection1:1": {"id": 1, "value": "updated"},
         "app/collection1:2": {"id": 2, "value": "new"},
         "app/collection2:1": {"id": 1, "key": "updated"},
-        "app/collection2:2": None,
+        "app/collection2:2": None,  # Deleted
     }
 
     element_cache.cache_provider.full_data = {
@@ -103,8 +103,8 @@ async def test_change_elements_with_no_data_in_redis(element_cache):
 
 
 @pytest.mark.asyncio
-async def test_get_all_full_data_from_db(element_cache):
-    result = await element_cache.get_all_full_data()
+async def test_get_all_data_from_db(element_cache):
+    result = await element_cache.get_all_data_list()
 
     assert result == example_data()
     # Test that elements are written to redis
@@ -119,7 +119,7 @@ async def test_get_all_full_data_from_db(element_cache):
 
 
 @pytest.mark.asyncio
-async def test_get_all_full_data_from_redis(element_cache):
+async def test_get_all_data_from_redis(element_cache):
     element_cache.cache_provider.full_data = {
         "app/collection1:1": '{"id": 1, "value": "value1"}',
         "app/collection1:2": '{"id": 2, "value": "value2"}',
@@ -127,14 +127,14 @@ async def test_get_all_full_data_from_redis(element_cache):
         "app/collection2:2": '{"id": 2, "key": "value2"}',
     }
 
-    result = await element_cache.get_all_full_data()
+    result = await element_cache.get_all_data_list()
 
     # The output from redis has to be the same then the db_data
     assert sort_dict(result) == sort_dict(example_data())
 
 
 @pytest.mark.asyncio
-async def test_get_full_data_change_id_0(element_cache):
+async def test_get_data_since_change_id_0(element_cache):
     element_cache.cache_provider.full_data = {
         "app/collection1:1": '{"id": 1, "value": "value1"}',
         "app/collection1:2": '{"id": 2, "value": "value2"}',
@@ -142,13 +142,13 @@ async def test_get_full_data_change_id_0(element_cache):
         "app/collection2:2": '{"id": 2, "key": "value2"}',
     }
 
-    result = await element_cache.get_full_data(0)
+    result = await element_cache.get_data_since(None, 0)
 
     assert sort_dict(result[0]) == sort_dict(example_data())
 
 
 @pytest.mark.asyncio
-async def test_get_full_data_change_id_lower_then_in_redis(element_cache):
+async def test_get_data_since_change_id_lower_then_in_redis(element_cache):
     element_cache.cache_provider.full_data = {
         "app/collection1:1": '{"id": 1, "value": "value1"}',
         "app/collection1:2": '{"id": 2, "value": "value2"}',
@@ -157,11 +157,11 @@ async def test_get_full_data_change_id_lower_then_in_redis(element_cache):
     }
     element_cache.cache_provider.change_id_data = {2: {"app/collection1:1"}}
     with pytest.raises(RuntimeError):
-        await element_cache.get_full_data(1)
+        await element_cache.get_data_since(None, 1)
 
 
 @pytest.mark.asyncio
-async def test_get_full_data_change_id_data_in_redis(element_cache):
+async def test_get_data_since_change_id_data_in_redis(element_cache):
     element_cache.cache_provider.full_data = {
         "app/collection1:1": '{"id": 1, "value": "value1"}',
         "app/collection1:2": '{"id": 2, "value": "value2"}',
@@ -172,7 +172,7 @@ async def test_get_full_data_change_id_data_in_redis(element_cache):
         1: {"app/collection1:1", "app/collection1:3"}
     }
 
-    result = await element_cache.get_full_data(1)
+    result = await element_cache.get_data_since(None, 1)
 
     assert result == (
         {"app/collection1": [{"id": 1, "value": "value1"}]},
@@ -181,12 +181,12 @@ async def test_get_full_data_change_id_data_in_redis(element_cache):
 
 
 @pytest.mark.asyncio
-async def test_get_full_data_change_id_data_in_db(element_cache):
+async def test_get_data_since_change_id_data_in_db(element_cache):
     element_cache.cache_provider.change_id_data = {
         1: {"app/collection1:1", "app/collection1:3"}
     }
 
-    result = await element_cache.get_full_data(1)
+    result = await element_cache.get_data_since(None, 1)
 
     assert result == (
         {"app/collection1": [{"id": 1, "value": "value1"}]},
@@ -195,27 +195,27 @@ async def test_get_full_data_change_id_data_in_db(element_cache):
 
 
 @pytest.mark.asyncio
-async def test_get_full_data_change_id_data_in_db_empty_change_id(element_cache):
+async def test_get_gata_since_change_id_data_in_db_empty_change_id(element_cache):
     with pytest.raises(RuntimeError):
-        await element_cache.get_full_data(1)
+        await element_cache.get_data_since(None, 1)
 
 
 @pytest.mark.asyncio
-async def test_get_element_full_data_empty_redis(element_cache):
-    result = await element_cache.get_element_full_data("app/collection1", 1)
+async def test_get_element_data_empty_redis(element_cache):
+    result = await element_cache.get_element_data("app/collection1", 1)
 
     assert result == {"id": 1, "value": "value1"}
 
 
 @pytest.mark.asyncio
-async def test_get_element_full_data_empty_redis_does_not_exist(element_cache):
-    result = await element_cache.get_element_full_data("app/collection1", 3)
+async def test_get_element_data_empty_redis_does_not_exist(element_cache):
+    result = await element_cache.get_element_data("app/collection1", 3)
 
     assert result is None
 
 
 @pytest.mark.asyncio
-async def test_get_element_full_data_full_redis(element_cache):
+async def test_get_element_data_full_redis(element_cache):
     element_cache.cache_provider.full_data = {
         "app/collection1:1": '{"id": 1, "value": "value1"}',
         "app/collection1:2": '{"id": 2, "value": "value2"}',
@@ -223,208 +223,14 @@ async def test_get_element_full_data_full_redis(element_cache):
         "app/collection2:2": '{"id": 2, "key": "value2"}',
     }
 
-    result = await element_cache.get_element_full_data("app/collection1", 1)
+    result = await element_cache.get_element_data("app/collection1", 1)
 
     assert result == {"id": 1, "value": "value1"}
 
 
-@pytest.mark.asyncio
-async def test_exists_restricted_data(element_cache):
-    element_cache.use_restricted_data_cache = True
-    element_cache.cache_provider.restricted_data = {
-        0: {
-            "app/collection1:1": '{"id": 1, "value": "value1"}',
-            "app/collection1:2": '{"id": 2, "value": "value2"}',
-            "app/collection2:1": '{"id": 1, "key": "value1"}',
-            "app/collection2:2": '{"id": 2, "key": "value2"}',
-        }
-    }
-
-    result = await element_cache.exists_restricted_data(0)
-
-    assert result
-
-
-@pytest.mark.asyncio
-async def test_exists_restricted_data_do_not_use_restricted_data(element_cache):
-    element_cache.use_restricted_data_cache = False
-    element_cache.cache_provider.restricted_data = {
-        0: {
-            "app/collection1:1": '{"id": 1, "value": "value1"}',
-            "app/collection1:2": '{"id": 2, "value": "value2"}',
-            "app/collection2:1": '{"id": 1, "key": "value1"}',
-            "app/collection2:2": '{"id": 2, "key": "value2"}',
-        }
-    }
-
-    result = await element_cache.exists_restricted_data(0)
-
-    assert not result
-
-
-@pytest.mark.asyncio
-async def test_del_user(element_cache):
-    element_cache.use_restricted_data_cache = True
-    element_cache.cache_provider.restricted_data = {
-        0: {
-            "app/collection1:1": '{"id": 1, "value": "value1"}',
-            "app/collection1:2": '{"id": 2, "value": "value2"}',
-            "app/collection2:1": '{"id": 1, "key": "value1"}',
-            "app/collection2:2": '{"id": 2, "key": "value2"}',
-        }
-    }
-
-    await element_cache.del_user(0)
-
-    assert not element_cache.cache_provider.restricted_data
-
-
-@pytest.mark.asyncio
-async def test_del_user_for_empty_user(element_cache):
-    element_cache.use_restricted_data_cache = True
-
-    await element_cache.del_user(0)
-
-    assert not element_cache.cache_provider.restricted_data
-
-
-@pytest.mark.asyncio
-async def test_update_restricted_data(element_cache):
-    element_cache.use_restricted_data_cache = True
-
-    await element_cache.update_restricted_data(0)
-
-    assert decode_dict(element_cache.cache_provider.restricted_data[0]) == decode_dict(
-        {
-            "app/collection1:1": '{"id": 1, "value": "restricted_value1"}',
-            "app/collection1:2": '{"id": 2, "value": "restricted_value2"}',
-            "app/collection2:1": '{"id": 1, "key": "restricted_value1"}',
-            "app/collection2:2": '{"id": 2, "key": "restricted_value2"}',
-            "_config:change_id": "0",
-        }
-    )
-    # Make sure the lock is deleted
-    assert not await element_cache.cache_provider.get_lock("restricted_data_0")
-
-
-@pytest.mark.asyncio
-async def test_update_restricted_data_full_restricted_elements(element_cache):
-    """
-    Tests that elements in the restricted_data cache, that are later hidden from
-    a user, gets deleted for this user.
-    """
-    element_cache.use_restricted_data_cache = True
-    await element_cache.update_restricted_data(0)
-    element_cache.cache_provider.change_id_data = {
-        1: {"app/collection1:1", "app/collection1:3"}
-    }
-
-    with patch("tests.unit.utils.cache_provider.restrict_elements", lambda x: []):
-        await element_cache.update_restricted_data(0)
-
-    assert decode_dict(element_cache.cache_provider.restricted_data[0]) == decode_dict(
-        {"_config:change_id": "1"}
-    )
-    # Make sure the lock is deleted
-    assert not await element_cache.cache_provider.get_lock("restricted_data_0")
-
-
-@pytest.mark.asyncio
-async def test_update_restricted_data_disabled_restricted_data(element_cache):
-    element_cache.use_restricted_data_cache = False
-
-    await element_cache.update_restricted_data(0)
-
-    assert not element_cache.cache_provider.restricted_data
-
-
-@pytest.mark.asyncio
-async def test_update_restricted_data_to_low_change_id(element_cache):
-    element_cache.use_restricted_data_cache = True
-    element_cache.cache_provider.restricted_data[0] = {"_config:change_id": "1"}
-    element_cache.cache_provider.change_id_data = {3: {"app/collection1:1"}}
-
-    await element_cache.update_restricted_data(0)
-
-    assert decode_dict(element_cache.cache_provider.restricted_data[0]) == decode_dict(
-        {
-            "app/collection1:1": '{"id": 1, "value": "restricted_value1"}',
-            "app/collection1:2": '{"id": 2, "value": "restricted_value2"}',
-            "app/collection2:1": '{"id": 1, "key": "restricted_value1"}',
-            "app/collection2:2": '{"id": 2, "key": "restricted_value2"}',
-            "_config:change_id": "3",
-        }
-    )
-
-
-@pytest.mark.asyncio
-async def test_update_restricted_data_with_same_id(element_cache):
-    element_cache.use_restricted_data_cache = True
-    element_cache.cache_provider.restricted_data[0] = {"_config:change_id": "1"}
-    element_cache.cache_provider.change_id_data = {1: {"app/collection1:1"}}
-
-    await element_cache.update_restricted_data(0)
-
-    # Same id means, there is nothing to do
-    assert element_cache.cache_provider.restricted_data[0] == {"_config:change_id": "1"}
-
-
-@pytest.mark.asyncio
-async def test_update_restricted_data_with_deleted_elements(element_cache):
-    element_cache.use_restricted_data_cache = True
-    element_cache.cache_provider.restricted_data[0] = {
-        "app/collection1:3": '{"id": 1, "value": "restricted_value1"}',
-        "_config:change_id": "1",
-    }
-    element_cache.cache_provider.change_id_data = {2: {"app/collection1:3"}}
-
-    await element_cache.update_restricted_data(0)
-
-    assert element_cache.cache_provider.restricted_data[0] == {"_config:change_id": "2"}
-
-
-@pytest.mark.asyncio
-async def test_update_restricted_data_second_worker(element_cache):
-    """
-    Test, that if another worker is updating the data, noting is done.
-
-    This tests makes use of the redis key as it would on different daphne servers.
-    """
-    element_cache.use_restricted_data_cache = True
-    element_cache.cache_provider.restricted_data = {0: {}}
-    await element_cache.cache_provider.set_lock("restricted_data_0")
-    await element_cache.cache_provider.del_lock_after_wait("restricted_data_0")
-
-    await element_cache.update_restricted_data(0)
-
-    # Restricted_data_should not be set on second worker
-    assert element_cache.cache_provider.restricted_data == {0: {}}
-
-
 @pytest.mark.asyncio
 async def test_get_all_restricted_data(element_cache):
-    element_cache.use_restricted_data_cache = True
-
-    result = await element_cache.get_all_restricted_data(0)
-
-    assert sort_dict(result) == sort_dict(
-        {
-            "app/collection1": [
-                {"id": 1, "value": "restricted_value1"},
-                {"id": 2, "value": "restricted_value2"},
-            ],
-            "app/collection2": [
-                {"id": 1, "key": "restricted_value1"},
-                {"id": 2, "key": "restricted_value2"},
-            ],
-        }
-    )
-
-
-@pytest.mark.asyncio
-async def test_get_all_restricted_data_disabled_restricted_data_cache(element_cache):
-    element_cache.use_restricted_data_cache = False
-    result = await element_cache.get_all_restricted_data(0)
+    result = await element_cache.get_all_data_list(0)
 
     assert sort_dict(result) == sort_dict(
         {
@@ -442,9 +248,7 @@ async def test_get_all_restricted_data_disabled_restricted_data_cache(element_ca
 
 @pytest.mark.asyncio
 async def test_get_restricted_data_change_id_0(element_cache):
-    element_cache.use_restricted_data_cache = True
-
-    result = await element_cache.get_restricted_data(0, 0)
+    result = await element_cache.get_data_since(0, 0)
 
     assert sort_dict(result[0]) == sort_dict(
         {
@@ -461,13 +265,12 @@ async def test_get_restricted_data_change_id_0(element_cache):
 
 
 @pytest.mark.asyncio
-async def test_get_restricted_data_disabled_restricted_data_cache(element_cache):
-    element_cache.use_restricted_data_cache = False
+async def test_get_restricted_data_2(element_cache):
     element_cache.cache_provider.change_id_data = {
         1: {"app/collection1:1", "app/collection1:3"}
     }
 
-    result = await element_cache.get_restricted_data(0, 1)
+    result = await element_cache.get_data_since(0, 1)
 
     assert result == (
         {"app/collection1": [{"id": 1, "value": "restricted_value1"}]},
@@ -477,19 +280,17 @@ async def test_get_restricted_data_disabled_restricted_data_cache(element_cache)
 
 @pytest.mark.asyncio
 async def test_get_restricted_data_change_id_lower_then_in_redis(element_cache):
-    element_cache.use_restricted_data_cache = True
     element_cache.cache_provider.change_id_data = {2: {"app/collection1:1"}}
 
     with pytest.raises(RuntimeError):
-        await element_cache.get_restricted_data(0, 1)
+        await element_cache.get_data_since(0, 1)
 
 
 @pytest.mark.asyncio
 async def test_get_restricted_data_change_with_id(element_cache):
-    element_cache.use_restricted_data_cache = True
     element_cache.cache_provider.change_id_data = {2: {"app/collection1:1"}}
 
-    result = await element_cache.get_restricted_data(0, 2)
+    result = await element_cache.get_data_since(0, 2)
 
     assert result == (
         {"app/collection1": [{"id": 1, "value": "restricted_value1"}]},