Adds schema caching capabilities (5s by default) (#2286)

* Adds schema caching capabilities (off by default)

* Use InMemoryCacheAdapter

* Uses proper adapter to generate a cache

* Fix bugs when running disabled cache

* nits

* nits

* Use options object instead of boolean

* Imrpove concurrency of loadSchema

* Adds testing with SCHEMA_CACHE_ON

* Use CacheController instead of generator

- Makes caching SchemaCache use a generated prefix
- Makes clearing the SchemaCache clear only the cached schema keys
- Enable cache by default (ttl 5s)

src/ParseServer.js

@@ -55,6 +55,7 @@ import { UsersRouter }          from './Routers/UsersRouter';
 import { PurgeRouter }          from './Routers/PurgeRouter';
 
 import DatabaseController       from './Controllers/DatabaseController';
+import SchemaCache              from './Controllers/SchemaCache';
 const SchemaController = require('./Controllers/SchemaController');
 import ParsePushAdapter         from 'parse-server-push-adapter';
 import MongoStorageAdapter      from './Adapters/Storage/Mongo/MongoStorageAdapter';
@@ -139,6 +140,7 @@ class ParseServer {
     expireInactiveSessions = true,
     verbose = false,
     revokeSessionOnPasswordReset = true,
+    schemaCacheTTL = 5, // cache for 5s
     __indexBuildCompletionCallbackForTests = () => {},
   }) {
     // Initialize the node client SDK automatically
@@ -197,7 +199,7 @@ class ParseServer {
     const userController = new UserController(emailControllerAdapter, appId, { verifyUserEmails });
     const liveQueryController = new LiveQueryController(liveQuery);
     const cacheController = new CacheController(cacheControllerAdapter, appId);
-    const databaseController = new DatabaseController(databaseAdapter);
+    const databaseController = new DatabaseController(databaseAdapter, new SchemaCache(cacheController, schemaCacheTTL));
     const hooksController = new HooksController(appId, databaseController, webhookKey);
     const analyticsController = new AnalyticsController(analyticsControllerAdapter);
 
@@ -254,6 +256,7 @@ class ParseServer {
       jsonLogs,
       revokeSessionOnPasswordReset,
       databaseController,
+      schemaCacheTTL
     });
 
     // To maintain compatibility. TODO: Remove in some version that breaks backwards compatability