Add Pool option queueLimit which enforces a maximum size of a Pool's queued connection requests. Fixes issue #475.

Author: marcuswestin

Readme.md

@@ -255,6 +255,9 @@ addition to those options pools accept a few extras:
   pool will immediately call back with an error. (Default: `true`)
 * `connectionLimit`: The maximum number of connections to create at once.
   (Default: `10`)
+* `queueLimit`: The maximum number of connection requests the pool will queue
+  before returning an error from `getConnection`. If set to `0`, there is no
+  limit to the number of queued connection requests. (Default: `0`)
 
 ## Switching users / altering connection state
 

lib/Pool.js

@@ -47,6 +47,10 @@ Pool.prototype.getConnection = function (cb) {
     return cb(new Error('No connections available.'));
   }
 
+  if (this.config.queueLimit && this._connectionQueue.length >= this.config.queueLimit) {
+    return cb(new Error('Queue limit reached.'));
+  }
+
   this._connectionQueue.push(cb);
 };
 

lib/PoolConfig.js

@@ -11,4 +11,7 @@ function PoolConfig(options) {
   this.connectionLimit    = (options.connectionLimit === undefined)
     ? 10
     : Number(options.connectionLimit);
+  this.queueLimit         = (options.queueLimit === undefined)
+    ? 0
+    : Number(options.queueLimit);
 }

test/integration/pool/test-queue-limit.js

@@ -0,0 +1,28 @@
+var common = require('../../common');
+var assert = require('assert');
+var pool   = common.createPool({
+  connectionLimit    : 1,
+  queueLimit         : 1,
+  waitForConnections : true
+});
+
+// First connection we get right away
+pool.getConnection(function(err, connection) {
+  connection.end()
+})
+
+// Second connection request goes into the queue
+pool.getConnection(function(err, connection) {
+  connection.end()
+  pool.end()
+})
+
+// Third connection request gets refused, since the queue is full
+var thirdGetErr
+pool.getConnection(function(err, connection) {
+  thirdGetErr = err
+})
+
+process.on('exit', function() {
+  assert.equal(thirdGetErr.message, 'Queue limit reached.')
+})