Add option to re-use schema cache between requests (#2979)

* Add option to reuse database controller between requests. Clear schema cache when deleting everything

* Add test

* Rename setting to persistSchemaCache to more accurately reflect effect

* Repurpose option to determine whether to randomize cache prefix. Restore Config.js controller creation. Add tests

* Fix bug with missing parameter passed to to SchemaCache

* Renaming and formatting

* Fix property name typo

* Rename option to avoid double negative and still be falsey by default. Style fix

src/Config.js

@@ -37,11 +37,12 @@ export class Config {
 
     // Create a new DatabaseController per request
     if (cacheInfo.databaseController) {
-      const schemaCache = new SchemaCache(cacheInfo.cacheController, cacheInfo.schemaCacheTTL);
+      const schemaCache = new SchemaCache(cacheInfo.cacheController, cacheInfo.schemaCacheTTL, cacheInfo.enableSingleSchemaCache);
       this.database = new DatabaseController(cacheInfo.databaseController.adapter, schemaCache);
     }
 
     this.schemaCacheTTL = cacheInfo.schemaCacheTTL;
+    this.enableSingleSchemaCache = cacheInfo.enableSingleSchemaCache;
 
     this.serverURL = cacheInfo.serverURL;
     this.publicServerURL = removeTrailingSlash(cacheInfo.publicServerURL);

src/Controllers/DatabaseController.js

@@ -515,7 +515,10 @@ DatabaseController.prototype.canAddField = function(schema, className, object, a
 // Returns a promise.
 DatabaseController.prototype.deleteEverything = function() {
   this.schemaPromise = null;
-  return this.adapter.deleteAllClasses();
+  return Promise.all([
+    this.adapter.deleteAllClasses(),
+    this.schemaCache.clear()
+  ]);
 };
 
 // Finds the keys in a query. Returns a Set. REST format only

src/Controllers/SchemaCache.js

@@ -8,13 +8,16 @@ import defaults from '../defaults';
 export default class SchemaCache {
   cache: Object;
 
-  constructor(cacheController, ttl = defaults.schemaCacheTTL) {
+  constructor(cacheController, ttl = defaults.schemaCacheTTL, randomizePrefix = false) {
     this.ttl = ttl;
     if (typeof ttl == 'string') {
       this.ttl = parseInt(ttl);
     }
     this.cache = cacheController;
-    this.prefix = SCHEMA_CACHE_PREFIX+randomString(20);
+    this.prefix = SCHEMA_CACHE_PREFIX;
+    if (!randomizePrefix) {
+      this.prefix += randomString(20);
+    }
   }
 
   put(key, value) {

src/ParseServer.js

@@ -139,6 +139,7 @@ class ParseServer {
     expireInactiveSessions = defaults.expireInactiveSessions,
     revokeSessionOnPasswordReset = defaults.revokeSessionOnPasswordReset,
     schemaCacheTTL = defaults.schemaCacheTTL, // cache for 5s
+    enableSingleSchemaCache = false,
     __indexBuildCompletionCallbackForTests = () => {},
   }) {
     // Initialize the node client SDK automatically
@@ -181,7 +182,7 @@ class ParseServer {
     const analyticsController = new AnalyticsController(analyticsControllerAdapter);
 
     const liveQueryController = new LiveQueryController(liveQuery);
-    const databaseController = new DatabaseController(databaseAdapter, new SchemaCache(cacheController, schemaCacheTTL));
+    const databaseController = new DatabaseController(databaseAdapter, new SchemaCache(cacheController, schemaCacheTTL, enableSingleSchemaCache));
     const hooksController = new HooksController(appId, databaseController, webhookKey);
 
     const dbInitPromise = databaseController.performInitizalization();
@@ -221,7 +222,8 @@ class ParseServer {
       jsonLogs,
       revokeSessionOnPasswordReset,
       databaseController,
-      schemaCacheTTL
+      schemaCacheTTL,
+      enableSingleSchemaCache
     });
 
     // To maintain compatibility. TODO: Remove in some version that breaks backwards compatability

src/cli/definitions/parse-server.js

@@ -195,6 +195,11 @@ export default {
     help: "The TTL for caching the schema for optimizing read/write operations. You should put a long TTL when your DB is in production. default to 0; disabled.",
     action: numberParser("schemaCacheTTL"),
   },
+  "enableSingleSchemaCache": {
+    env: "PARSE_SERVER_ENABLE_SINGLE_SCHEMA_CACHE",
+    help: "Use a single schema cache shared across requests. Reduces number of queries made to _SCHEMA. Defaults to false, i.e. unique schema cache per request.",
+    action: booleanParser
+  },
   "cluster": {
     help: "Run with cluster, optionally set the number of processes default to os.cpus().length",
     action: numberOrBoolParser("cluster")