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From Shawn Heisey <apa...@elyograg.org>
Subject Re: xms/xmx choices
Date Thu, 05 Dec 2019 19:41:36 GMT
On 12/5/2019 11:58 AM, David Hastings wrote:
> as of now we do an xms of 8gb and xmx of 60gb, generally through the
> dashboard the JVM hangs around 16gb.  I know Xms and Xmx are supposed to be
> the same so thats the change #1 on my end, I am just concerned of dropping
> it from 60 as thus far over the last few years I have had no problems nor
> performance issues.  I know its said a lot of times to make it lower and
> let the OS use the ram for caching the file system/index files, so my first
> experiment was going to be around 20gb, was wondering if this seems sound,
> or should i go even lower?

The Xms and Xmx settings should be the same so Java doesn't need to take 
special action to increase the pool size when more than the minimum is 
required.  Java tends to always increase to the maximum as it runs, so 
there's usually little benefit to specifying a lower minimum than the 
maximum.  With a 60GB max heap, Java is likely to grab a little more 
than 60GB from the OS, regardless of how much heap is actually in use.

If you can provide GC logs from Solr that cover a signficant timeframe, 
especially heavy indexing, we can analyze those and make an estimate 
about the values you should have for Xms and Xmx.  It will only be a 
guess ... something might happen later that requires more heap.

We can't make recommendations without hard data.  The information you 
provided isn't enough to guess how much heap you'll need.  Depending on 
how such a system is used, a few GB might be enough, or you might need a 
lot more.

https://lucidworks.com/post/sizing-hardware-in-the-abstract-why-we-dont-have-a-definitive-answer/

Thanks,
Shawn

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