adding comments

engines/gaugesEngine.js

@@ -20,14 +20,18 @@ MySQLBackendGaugesEngine.prototype.buildQuerries = function(gauges, time_stamp)
       if(gaugeValue === 0) {
         continue;
       } else {
-        /**********************************************************************
-         * Edit following line to custumize where statsd datas are inserted
-         *
-         * Parameters :
-         *    - userCounterName: Counter name
-         *    - counterValue: Counter value
-         */
-        //querries.push("insert into `gauges_statistics` values ("+time_stamp+", '"+gaugeName+"', "+gaugeValue+");");
+          /**********************************************************************
+           * Edit following line to customize where statsd datas are inserted
+           *
+           * Parameters :
+           *    - gaugeName: Gauge name
+           *    - gaugeValue: Gauge value
+           */
+          // This SQL request checks if the last value for this particular gauge is the same as  gaugeValue.
+          // If it is the same, we do nothing.
+          // If it is different, we insert a new line.
+          // If gaugeName does not exist in the table, we insert a new line
+          // The -678 value, is totally arbitrary, I just assumed that there was never gonna be a gauge with a -678 value. You can change it to any value not used by your gauges ;)
         querries.push("insert into `gauges_statistics` select "+time_stamp+", '"+gaugeName+"', "+gaugeValue+" from dual where (select if(max(value),max(value),-678) from `gauges_statistics` where name = '"+gaugeName+"') = -678 OR (select value from `gauges_statistics` where name = '"+gaugeName+"' order by timestamp desc limit 0,1) <> "+gaugeValue+";")
 
       }