Getting worse search performance with a replica shard

Question

To increase search performance, I tried to add a replica to my cluster. Initially, I measured a response time of around 700ms for a specific request with a single node with a primary shard. After adding a node and a replica shard to the cluster, it takes averagely 2000ms to get the result of the request (so it almost tripled).

I'm using these configs for the replica :

cluster.name: findmyfpstore
node.name: fmfs_r1
node.master: false
network.host: ...
http.port: ...
discovery.zen.ping.multicast.enabled: false
discovery.zen.ping.unicast.hosts: ['...']
index.number_of_shards: 1
index.number_of_replicas: 1

Am I doing something wrong ? Feel free to tell me if you need more informations, I'm a beginner at ElasticSearch.

Thanks a lot!

EDIT: I tried with 2 shards, 1 replica, it doesn't change much

How many Elasticsearch nodes are you running? What sort of specs are these machines? Are you using SSD? — Or Weinberger
Hi, there are two nodes, each of the nodes are running on one different server (32go RAM, 8 cores). They don't use SSD. — azekirel555
Since you're using a single shard, I'm not sure you would see any significant performance boost by adding a replica, however, you also shouldn't get any performance hit because of it. What happens if you use 2 shards and 1 replica? — Or Weinberger
Are multiple shards useful if the data volume is really low ? I only have < 1k documents and it probably won't be higher. I'm trying it and I'll give you the results as soon as possible. — azekirel555
What is your document size? Can you share your query? Maybe we can improve that.. — Or Weinberger

Or Weinberger Or Weinberger · Accepted Answer · 2016-09-19T14:17:54

There are a lot of elements that can affect the performance of your cluster and query speeds.

I suggest you follow Elasticsearch's Production Deployment document, this will give you a lot of insight on how to properly configure your cluster.

Getting worse search performance with a replica shard

1 Answers