Bad performance of 2-node-cluster

Elastic Stack Elasticsearch
1

Hey,
I have about 7 million documents in my ES cluster using default
configurations (5 shards, 1 replica).
I set up 4 virtual machines with similar configurations on a 8 core server,
each virtual machine assigned with 2 virtual cores and 4 GB memory. On each
node I installed Elasticsearch.
I did several search tests to measure query response time and the results
are a bit confusing:

  1. When using only a single node, I get the best response time.
  2. When using a 2-node cluster response time increases significantly,
    meaning the response time gets worse (the more found documents the worse
    the response time)
  3. For a three- or four-node cluster the response time improves again and
    is at the level of the single-node configuration.

Any idea why the 2-node cluster has such a bad performance compared to the
other configurations?

cheers
Herbert

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2

Why do you set up more than one JVM per machine?

Jörg

On Wed, Mar 19, 2014 at 10:36 AM, Herbert Bodner
herbert.bodner@gmail.comwrote:

Hey,
I have about 7 million documents in my ES cluster using default
configurations (5 shards, 1 replica).
I set up 4 virtual machines with similar configurations on a 8 core
server, each virtual machine assigned with 2 virtual cores and 4 GB memory.
On each node I installed Elasticsearch.
I did several search tests to measure query response time and the results
are a bit confusing:

  1. When using only a single node, I get the best response time.
  2. When using a 2-node cluster response time increases significantly,
    meaning the response time gets worse (the more found documents the worse
    the response time)
  3. For a three- or four-node cluster the response time improves again and
    is at the level of the single-node configuration.

Any idea why the 2-node cluster has such a bad performance compared to the
other configurations?

cheers
Herbert

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3

Why do you set up more than one JVM per machine?

I didn´t do that!? One Elasticsearch-Installation on each of the four
virtual machines.

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4

I guess I found the problem: The results that 2 nodes perform much worse,
cannot be reproduced.
There has been going on something else on the server at that time when I
executed the tests for 2 nodes, which influenced the results. (Probably
somebody copied a large file to or from the server, which made the disk
kind of busy)

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