How to set elasticsearch jvm heap size?

Elastic Stack Elasticsearch
#1

If I have a 16C64G machine and install CentOS7.6 on it, There is 62gb available memory.

             total        used        free      shared  buff/cache   available
Mem:             62          34           0           0          27          27
Swap:             0           0           0

According to the reference, I have 3 choices to set the jvm heap size:
31.5gb: The largest size I can set If I want to use compressed object pointers (compressed oops)
31gb: half of the system memory and use compressed object pointers (compressed oops)
30gb: The largest size I can set if I want to use zero based compressed oops.

So which is the best practise?

#2

Half of the system, up to just under 32GB. You will want to check in your Elasticsearch logs at startup if it's using compressed pointers if you get near 31-32GB.

#3

So you mean 31gb is the best,right?
I want to know if it is worth to reduce 1gb memory, from 31gb to 30gb, to use zero based compressed oops.

#4

It 100% is.
Otherwise you need (from memory) about 40+ gig of heap to store the same amount.

#5

Sorry I didn't express it clearly.
I just want to compare zero based compressed oops with compressed oops, both of them(30gb and 31gb) use the compressed object pointers.

#6

The reference manual contains clear instructions:

Set Xmx and Xms to no more than the threshold for zero-based compressed oops.

You can ignore this instruction at your own risk, but if you want to know the recommended practice then that's what it is.

#7

I know the threshold value of compressed oops and zero-based compressed oops.
But I don't know which one is better.
Theoretically zero-based compressed oops has better performance than compressed oops, but if I want to use it ,the largest value must be no more than 30gb. 1gb less than 31gb with compressed oops.

#8

It's better to stick to what the manual says.

#9

So 30gb is better, because it meets all recommendations in the manual, right?

#10

The exact threshold varies from JVM to JVM, I don't think 30GB is always low enough but it often is. As long as your JVM reports that it's using zero-based compressed oops, it's all good.

#11

OK,thanks.

#12

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