php memcache client performance

I am benchmarking an app I made which uses repcached (memcached with replication) for storing objects and taking some load off the db.

While benchmarking the index page I run

ab -c 400 -n 5000 http://mysite

When I use just one memcache server wit开发者_如何学Ch

list($server, $port) = explode(':', $settings->memcached_servers[0]);
$this->link = new Memcache();
$this->link->connect($server, (int) $port);

I get 1000 reqs/sec

When I out more than one server to the pool with

$this->link = new Memcache();
foreach($settings->memcached_servers as $server){
  list($server, $port) = explode(':', $server);
  $this->link->addServer($server, (int) $port, 0, 10);
}

I only get 300 reqs/sec

The difference is huge

Any idea why?

I really need to have 2 server for redundancy but the performance is also crucial

It it normal to have such a huge difference?

Basically, the index page makes justs 2 calls to the db getting just one row, so the rows are cached while running the test.

But I am surprised to see memcached fall so much behind in the test.

Well it seems that the culprit was the weight parameter of the addServer

Changing it to 1 for the 1st server and 2 for the second did it and performance is now the same