We have a Solr server running on 64-bit Windows 2008, and under the
default Tomcat settings it seems to be using a small fraction of the
available memory (fluctuating between 100Mb and 300Mb: see trace from
VisualVM at http://imgur.com/4Om2El&tqLKW <http://imgur.com/4Om2El&tqLKW> )
I was advised that, to increase performance, we should increase the
amount of memory allocated to Tomcat so that Solr could use this to
cache query results and so reduce CPU usage and disk I/O. So, I set both
the min and max RAM allocation for Tomcat to 10Gb, which is well within
the amount allocated to the server (16Gb). I tried this on another
machine, set a simulated load of lots of concurrent users running on our
application, and the VisualVM results can be seen at
http://imgur.com/4Om2E&tqLKWl <http://imgur.com/4Om2E&tqLKWl>
These results were very different: in the first half of the graph, when
the system was under load, the amount of allocated heap size was fixed
at 10Gb, which I would expect, but the amount of used heap climbed
gradually to around 3Gb, but then shot right down again to something
close to zero every minute or so, presumably due to the GC kicking in,
giving the sawtooth pattern you can see in the screenshot above.
My question is: is this normal and expected? I would have thought that
the amount of used heap would climb to somewhere much nearer the maximum
available of 10Gb, rather than peaking at a mere 3Gb. And also that any
garbage collection would only deallocate part of the memory rather than
knocking it right back to zero.
Essentially, why isn't Solr using more of the memory assigned, and using
it constantly rather than continually clearing the cache?
Thanks,
-Tristan.
- Solr not using allocated memory? Tristan Roddis
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