Add GC limit for expired clients per cycle

If the set of clients is really large, the ZRANGEBYSCORE Redis command
can overwhelm the process by taking too much time and too much
memory. Setting the `gc_limit` option will now set the LIMIT parameter
on that command, allowing the GC cycle to finish within a reasonable
amount of time. Also adds some logging.

Author: daveyeu

faye-redis.js

@@ -159,6 +159,11 @@ multiRedis.COMMANDS.forEach(function(command) {
 //                         number of seconds. To completely disable GC, set this
 //                         to `false`.
 //
+//   gc_limit              By default, the GC tries to prune all expired
+//                         clients. This can be set to an integer, however, to
+//                         limit the number of expired clients to process in a
+//                         given GC cycle. Highly recommended.
+//
 var Engine = function(server, options) {
   this._options = options || {};
 
@@ -181,6 +186,7 @@ var Engine = function(server, options) {
   }
 
   if (gc) {
+    this._gc_limit = this._options.gc_limit;
     this._gc = setInterval(function() { self.gc() }, gc * 1000);
   }
 };
@@ -350,23 +356,36 @@ Engine.prototype = {
     if (typeof timeout !== 'number') return;
 
     this._redis.urls.forEach(function(url) {
+      console.log("[" + url + "] Running GC");
       var connection = this._redis.connections[url];
 
       this._withLock(connection, 'gc', function(releaseLock) {
         var cutoff = new Date().getTime() - 1000 * 2 * timeout,
-            self   = this;
+            self   = this,
+            args;
 
-        connection.zrangebyscore(this._ns + '/clients', 0, cutoff, function(error, clients) {
+        var pruneClientsCallback = function pruneClientsCallback(error, clients) {
           var i = 0, n = clients.length;
           if (i === n) return releaseLock();
 
           clients.forEach(function(clientId) {
             this.destroyClient(clientId, function() {
               i += 1;
-              if (i === n) releaseLock();
+              if (i === n) {
+                console.log("[" + url + "] Destroyed " + n + " expired clients");
+                releaseLock();
+              }
             }, this);
           }, self);
-        });
+        };
+
+        if (this._gc_limit) {
+          args = [this._ns + "/clients", 0, cutoff, "LIMIT", 0, this._gc_limit, pruneClientsCallback];
+        } else {
+          args = [this._ns + "/clients", 0, cutoff, pruneClientsCallback];
+        }
+
+        connection.zrangebyscore.apply(connection, args);
       }, this);
     }, this);
   },

package.json

@@ -4,7 +4,7 @@
 , "author"          : "James Coglan <jcoglan@gmail.com> (http://jcoglan.com/)"
 , "keywords"        : ["pubsub", "bayeux"]
 
-, "version"         : "0.1.6"
+, "version"         : "0.1.7"
 , "engines"         : {"node": ">=0.4.0"}
 , "main"            : "./faye-redis"
 , "dependencies"    : {"hiredis": "", "redis": "", "consistent-hashing": ""}