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From David Hastings <hastings.recurs...@gmail.com>
Subject Re: xms/xmx choices
Date Thu, 05 Dec 2019 19:52:25 GMT
I know theres no hard answer, and I know the Xms and Xmx should be the
same, but it was a set it and forget it sort of thing from years ago.  I
will definitely be changing it but figured I may as well figure out as
much as possible from this user group resource.
as far as the raw GC data goes:
https://pastebin.com/vBtpYR1W

(i dont know if people still use pastebin)  i can get more if needed.  the
systems dont do ANY indexing at all, they are search only slaves.  they
share resources only with a DB install, and one node will never do both
live search and live DB.  If theres any more info youd like I would be
happy to provide, this is interesting.

On Thu, Dec 5, 2019 at 2:41 PM Shawn Heisey <apache@elyograg.org> wrote:

> 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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