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From Shawn Heisey <apa...@elyograg.org>
Subject Re: Java 9
Date Mon, 06 Nov 2017 23:24:22 GMT
On 11/6/2017 3:07 PM, Petersen, Robert (Contr) wrote:
> Anyone else been noticing this this msg when starting up solr with java 9? (This is just
an FYI and not a real question)
>
> Java HotSpot(TM) 64-Bit Server VM warning: Option UseConcMarkSweepGC was deprecated in
version 9.0 and will likely be removed in a future release.
> Java HotSpot(TM) 64-Bit Server VM warning: Option UseParNewGC was deprecated in version
9.0 and will likely be removed in a future release.

I have not tried Java 9 yet.

Looks like G1 is now the default garbage collector.  I did not know that
they were deprecating CMS and ParNew ... that's a little surprising. 
Solr's default garbage collection tuning uses those two collectors.  It
is likely that those choices will be available in all versions of Java
9.  It would be very uncharacteristic for Oracle to take action on
removing them until version 10, possibly later.

If it were solely up to me, I would adjust Solr's startup script to use
the G1 collector by default, eliminating the warnings you're seeing. 
It's not just up to me though.  Lucene documentation says to NEVER use
the G1 collector because they believe it to be unpredictable and have
the potential to cause problems.  I personally have never had any issues
with it.  There is *one* Lucene issue mentioning problems with G1GC, and
that issue is *specific* to the 32-bit JVM, which is not recommended
because of the limited amount of memory it can use.

My experiments with GC tuning show the G1 collector (now default in Java
9) to have very good characteristics with Solr.  I have a personal page
on the Solr wiki that covers those experiments.

https://wiki.apache.org/solr/ShawnHeisey

Thanks,
Shawn


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