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I have integrated twemproxy into web layer and I have 6 Elasticache(1 master , 5 read replicas) I am getting issue that the all replicas have same keys everything is same but cache hits on one replica is way more than others and I performed several load testing still on every test I am getting same result. I have separate data engine that writes on the master of this cluster and remaining 5 replicas get sync with it. So I am using twemproxy only for reading data from Elasticache not for sharding purpose. So my simple question is why i am getting 90% of hits on single read replicas of Elasticache it should distribute the hits evenly among all read replicas? right?

Thank you in advance

Rohit
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Twemproxy hashes everything as I recall. This means it will try to split keys among the masters you give it. If you have one master this means it hashes everything to one server. Thus, as far as it is concerned you have one server for acceptable queries. As such, it isn't helping you in this case.

If you want to have a single endpoint to distribute reads across a bank of identical slaves, you will need to put a TCP load balancer in front of the slaves and have your application talk to the IP:port of the load balancer. Common options are Nginx and HAProxy for software based ones, on AWS you could use their load balancer but you could run into various resource limits out of your control there, and pretty much any hardware load balancer would work as well (though this is difficult if not impossible on AWS).

Which load balancer to use is dependent on your (or your personnel's) comfort and knowledge level with each option.

The Real Bill
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  • But as I mentioned we are not using Twemproxy for hashing we are just using it for read purpose. – Rohit Sep 07 '15 at 10:16
  • Twemproxy always hashes, that is what it is made to do. Unless you modified the source code yourself. With a single acceptable server all keys will hash to the one slot it has. So, one server. Or, you have a hot shard. Or both. Either way, whether you want it to or not, Twemproxy is hashing the data. – The Real Bill Sep 10 '15 at 02:34