improve admin rpc for diagnosing memory used by the cache

lib/commands/admin-rpc.js

@@ -20,22 +20,36 @@ var getFileDescriptorLimit = function (env, server, cb) {
 };
 
 var getCacheStats = function (env, server, cb) {
+    var metaSize = 0;
+    var channelSize = 0;
     var metaCount = 0;
     var channelCount = 0;
 
+    try {
         var meta = env.metadata_cache;
         for (var x in meta) {
-        if (meta.hasOwnProperty(x)) { metaCount++; }
+            if (meta.hasOwnProperty(x)) {
+                metaCount++;
+                metaSize += JSON.stringify(meta[x]).length;
+            }
         }
 
         var channels = env.channel_cache;
         for (var y in channels) {
-        if (channels.hasOwnProperty(y)) { channelCount++; }
+            if (channels.hasOwnProperty(y)) {
+                channelCount++;
+                channelSize += JSON.stringify(channels[y]).length;
+            }
+        }
+    } catch (err) {
+        return void cb(err && err.message);
     }
 
     cb(void 0, {
         metadata: metaCount,
+        metaSize: metaSize,
         channel: channelCount,
+        channelSize: channelSize,
     });
 };