We have configured Elastic Search JVM options /etc/elasticsearch/jvm.options to use a fixed heap size of -Xms512m -Xmx512m

This can be confirmed as working when checking the Elastic Search process:

enter image description here

However you'll notice that it's still using 835M of memory.

If we check the actual used heap size with ES:

root: curl -sS -XGET "localhost:9200/_cat/nodes?h=heap*&v"
heap.current heap.percent heap.max
     276.1mb           55  494.9mb

It's actually only using 276MB of the heap - so where is the other 559MB being used exactly? We're concerned it's causing a lot of swap/paging issues, particularly as the VIRT column has a size of 4GB (but I'm told not to worry about that column, though it does seem a strangely high number to me)

We've also disabled swapping for Elastic Search with the mlockall option, which can be confirmed with:

root:~# curl -s localhost:9200/_nodes?pretty|grep mlock
     "mlockall" : true

However it seems it's STILL swapping:

for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done | sort -k 2 -n -r | less
java 128592 kB

So my questions are:

  1. What can we do to reduce the size of memory consumed by Elastic Search to ensure it's fixed at 512MB or as close to that as possible?
  2. Ensure swapping is disabled
  3. Reduce size of the VIRT column (or is this really not worth worrying about?)

This setting only limits the RAM that the Elasticsearch Application (inside your JVM) is using, it does not limit the amount of RAM that the JVM needs for overhead. The same goes for mlockall

That is why Elastic suggests using 50% of the available RAM (after OS and other running software) for your Elasticsearch application with -Xmx.

Good article about it: Why does my Java process consume more memory than Xmx

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I would recommend you check the documentation regarding heap size

Anyway, I think it is absolutely recommended to not assign less than 1GB memory to elasticsearch service on a production server.

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