add explain cache and cache status route

app/controllers/app.js

@@ -20,17 +20,23 @@ var express = require('express')
     }))
     , Step        = require('step')
     , csv         = require('csv')
+    , crypto      = require('crypto')
     , Meta        = require(global.settings.app_root + '/app/models/metadata')
     , oAuth       = require(global.settings.app_root + '/app/models/oauth')
     , PSQL        = require(global.settings.app_root + '/app/models/psql')
     , ApiKeyAuth  = require(global.settings.app_root + '/app/models/apikey_auth')
-    , _        = require('underscore');
+    , _           = require('underscore')
+    , tableCache  = {};
 
 app.use(express.bodyParser());
 app.enable('jsonp callback');
 
+// basic routing
 app.all('/api/v1/sql',     function(req, res) { handleQuery(req, res) } );
 app.all('/api/v1/sql.:f',  function(req, res) { handleQuery(req, res) } );
+app.get('/api/v1/cachestatus',  function(req, res) { handleCacheStatus(req, res) } );
+
+// request handlers
 function handleQuery(req, res){
 
     // sanitize input
@@ -54,6 +60,9 @@ function handleQuery(req, res){
     // setup step run
     var start = new Date().getTime();
 
+    // initialise MD5 key of sql for cache lookups
+    var sql_md5 = generateMD5(sql);
+
     try {
         if (!_.isString(sql)) throw new Error("You must indicate a sql query");
         var pg, explain_result;
@@ -81,14 +90,23 @@ function handleQuery(req, res){
                 // store postgres connection
                 pg = new PSQL(user_id, database, limit, offset);
 
-                // get all the tables
+                // get all the tables from Cache or SQL
+
+                if (!_.isNull(tableCache[sql_md5]) && !_.isUndefined(tableCache[sql_md5])){
+                   tableCache[sql_md5].hits++;
+                   return true;
+                } else{
                     pg.query("SELECT CDB_QueryTables($$" + sql + "$$)", this);
+                }
             },
             function queryResult(err, result){
                 if (err) throw err;
 
-                // store explain result
+                // store explain result in local Cache
-                explain_result = result;
+                if (_.isUndefined(tableCache[sql_md5])){
+                    tableCache[sql_md5] = result;
+                    tableCache[sql_md5].hits = 1; //initialise hit counter
+                }
 
                 // TODO: refactor formats to external object
                 if (format === 'geojson'){
@@ -110,7 +128,7 @@ function handleQuery(req, res){
                 // set cache headers
                 res.header('Last-Modified', new Date().toUTCString());
                 res.header('Cache-Control', 'no-cache,max-age=3600,must-revalidate, public');
-                res.header('X-Cache-Channel', generateCacheKey(database,explain_result));
+                res.header('X-Cache-Channel', generateCacheKey(database, tableCache[sql_md5]));
 
                 return result;
             },
@@ -147,6 +165,15 @@ function handleQuery(req, res){
     }
 }
 
+function handleCacheStatus(req, res){
+    var tableCacheValues = _.values(tableCache);
+    var totalExplainHits = _.reduce(tableCacheValues, function(memo, res) { return memo + res.hits}, 0);
+    var totalExplainKeys = tableCacheValues.length;
+
+    res.send({explain: {hits: totalExplainHits, keys : totalExplainKeys }});
+}
+
+// helper functions
 function toGeoJSON(data, res, callback){
     try{
         var out = {
@@ -218,6 +245,12 @@ function generateCacheKey(database,tables){
     return database + ":" + tables.rows[0].cdb_querytables.split(/^\{(.*)\}$/)[1];   
 }
 
+function generateMD5(data){
+    var hash = crypto.createHash('md5');
+    hash.update(data);
+    return hash.digest('hex');
+}
+
 function handleException(err, res){
     var msg = (global.settings.environment == 'development') ? {error:[err.message], stack: err.stack} : {error:[err.message]}
     if (global.settings.environment !== 'test'){