Add a cache decorator over QueryTables

app/app.js

@@ -188,7 +188,7 @@ function App() {
     var genericController = new GenericController();
     genericController.route(app);
 
-    var queryController = new QueryController(userDatabaseService, statsd_client);
+    var queryController = new QueryController(userDatabaseService, tableCache, statsd_client);
     queryController.route(app);
 
     var jobController = new JobController(userDatabaseService, jobBackend, jobCanceller);

app/controllers/query_controller.js

@@ -4,7 +4,7 @@ var _ = require('underscore');
 var step = require('step');
 var assert = require('assert');
 var PSQL = require('cartodb-psql');
-var QueryTables = require('cartodb-query-tables');
+var CachedQueryTables = require('../services/cached-query-tables');
 var AuthApi = require('../auth/auth_api');
 var queryMayWrite = require('../utils/query_may_write');
 
@@ -19,9 +19,10 @@ var ONE_YEAR_IN_SECONDS = 31536000; // 1 year time to live by default
 
 var cdbReq = new CdbRequest();
 
-function QueryController(userDatabaseService, statsd_client) {
+function QueryController(userDatabaseService, tableCache, statsd_client) {
     this.statsd_client = statsd_client;
     this.userDatabaseService = userDatabaseService;
+    this.queryTables = new CachedQueryTables(tableCache);
 }
 
 QueryController.prototype.route = function (app) {
@@ -136,7 +137,7 @@ QueryController.prototype.handleQuery = function (req, res) {
 
                 var pg = new PSQL(authDbParams, {}, { destroyOnError: true });
 
-                QueryTables.getAffectedTablesFromQuery(pg, sql, function(err, result) {
+                self.queryTables.getAffectedTablesFromQuery(pg, sql, function(err, result) {
                     if (err) {
                         var errorMessage = (err && err.message) || 'unknown error';
                         console.error("Error on query explain '%s': %s", sql, errorMessage);

app/services/cached-query-tables.js

@@ -0,0 +1,38 @@
+var QueryTables = require('cartodb-query-tables');
+
+var generateMD5 = require('../utils/md5');
+
+function CachedQueryTables(tableCache) {
+    this.tableCache = tableCache;
+}
+
+module.exports = CachedQueryTables;
+
+CachedQueryTables.prototype.getAffectedTablesFromQuery = function(pg, sql, callback) {
+    var self = this;
+
+    var cacheKey = sqlCacheKey(pg.username(), sql);
+    var cachedResult = this.tableCache.get(cacheKey);
+
+    if (cachedResult) {
+        cachedResult.hits++;
+        return callback(null, cachedResult.result);
+    } else {
+        QueryTables.getAffectedTablesFromQuery(pg, sql, function(err, result) {
+            if (err) {
+                return callback(err);
+            }
+
+            self.tableCache.set(cacheKey, {
+                result: result,
+                hits: 1
+            });
+
+            return callback(null, result);
+        });
+    }
+};
+
+function sqlCacheKey(user, sql) {
+    return user + ':' + generateMD5(sql);
+}