Improve single schema cache (#7214)

* Initial Commit

* fix flaky test

* temporary set ci timeout

* turn off ci check

* fix postgres tests

* fix tests

* node flaky test

* remove improvements

* Update SchemaPerformance.spec.js

* fix tests

* revert ci

* Create Singleton Object

* properly clear cache testing

* Cleanup

* remove fit

* try PushController.spec

* try push test rewrite

* try push enqueue time

* Increase test timeout

* remove pg server creation test

* xit push tests

* more xit

* remove skipped tests

* Fix conflicts

* reduce ci timeout

* fix push tests

* Revert "fix push tests"

This reverts commit 05aba62f1cbbca7d5d3e80b9444529f59407cb56.

* improve initialization

* fix flaky tests

* xit flaky test

* Update CHANGELOG.md

* enable debug logs

* Update LogsRouter.spec.js

* create initial indexes in series

* lint

* horizontal scaling documentation

* Update Changelog

* change horizontalScaling db option

* Add enableSchemaHooks option

* move enableSchemaHooks to databaseOptions

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -113,12 +113,15 @@ export class MongoStorageAdapter implements StorageAdapter {
   _uri: string;
   _collectionPrefix: string;
   _mongoOptions: Object;
+  _onchange: any;
+  _stream: any;
   // Public
   connectionPromise: ?Promise<any>;
   database: any;
   client: MongoClient;
   _maxTimeMS: ?number;
   canSortOnJoinTables: boolean;
+  enableSchemaHooks: boolean;
 
   constructor({ uri = defaults.DefaultMongoURI, collectionPrefix = '', mongoOptions = {} }: any) {
     this._uri = uri;
@@ -126,13 +129,20 @@ export class MongoStorageAdapter implements StorageAdapter {
     this._mongoOptions = mongoOptions;
     this._mongoOptions.useNewUrlParser = true;
     this._mongoOptions.useUnifiedTopology = true;
+    this._onchange = () => {};
 
     // MaxTimeMS is not a global MongoDB client option, it is applied per operation.
     this._maxTimeMS = mongoOptions.maxTimeMS;
     this.canSortOnJoinTables = true;
+    this.enableSchemaHooks = !!mongoOptions.enableSchemaHooks;
+    delete mongoOptions.enableSchemaHooks;
     delete mongoOptions.maxTimeMS;
   }
 
+  watch(callback: () => void): void {
+    this._onchange = callback;
+  }
+
   connect() {
     if (this.connectionPromise) {
       return this.connectionPromise;
@@ -198,7 +208,13 @@ export class MongoStorageAdapter implements StorageAdapter {
   _schemaCollection(): Promise<MongoSchemaCollection> {
     return this.connect()
       .then(() => this._adaptiveCollection(MongoSchemaCollectionName))
-      .then(collection => new MongoSchemaCollection(collection));
+      .then(collection => {
+        if (!this._stream && this.enableSchemaHooks) {
+          this._stream = collection._mongoCollection.watch();
+          this._stream.on('change', () => this._onchange());
+        }
+        return new MongoSchemaCollection(collection);
+      });
   }
 
   classExists(name: string) {