bq: If you know the maximum size you ever will need, setting Xmx is good. Not quite sure what you're getting at here. I pretty much guarantee that a production system will eat up the default heap size, so not setting Xmx will cause OOM errors pretty soon. Or did you mean Xms?
As far as setting Xms, there are differing opinions, mostly though since Solr likes memory so much there's a lot of tuning to try to determine Xmx and it's pretty much guaranteed that Java will need close to that amount of memory. So setting Xms=Xmx is a minor optimization if that assumption is true. It's arguable how much practical difference it makes though. Best, Erick On Mon, Nov 28, 2016 at 2:14 AM, Florian Gleixner <f...@redflo.de> wrote: > Am 28.11.2016 um 00:00 schrieb Shawn Heisey: >> >> On 11/27/2016 12:51 PM, Florian Gleixner wrote: >>> >>> On 22.11.2016 14:54, Max Bridgewater wrote: >>>> >>>> test cases were exactly the same, the machines where exactly the same >>>> and heap settings exactly the same (Xms24g, Xmx24g). Requests were >>>> sent with >>> >>> Setting heap too large is a common error. Recent Solr use the >>> filesystem cache, so you don't have to set heap to the size of the >>> index. The avalible RAM has to be able to run the OS, run the jvm and >>> hold most of the index data in filesystem cache. If you have 32GB RAM >>> and a 20GB Index, then set -Xms never higher than 10GB. I personally >>> would set -Xms to 4GB and omit -Xmx >> >> >> In my mind, the Xmx setting is much more important than Xms. Setting >> both to the same number avoids any need for Java to detect memory >> pressure before increasing the heap size, which can be helpful. >> > > From https://cwiki.apache.org/confluence/display/solr/JVM+Settings > > "The maximum heap size, set with -Xmx, is more critical. If the memory heap > grows to this size, object creation may begin to fail and throw > OutOfMemoryException. Setting this limit too low can cause spurious errors > in your application, but setting it too high can be detrimental as well." > > you are right, Xmx is more important. But setting Xms to Xmx will waste RAM, > that the OS can use to cache your index data. Setting Xmx can avoid problems > in some situations where solr can eat up your filesystem cache until the > next GC has been finished. > >> Without Xmx, Java is in control of the max heap size, and it may not >> make the correct choice. It's important to know what your max heap is, >> because chances are excellent that the max heap *will* be reached. Solr >> allocates a lot of memory to do its job. >> > > If you know the maximum size you ever will need, setting Xmx is good. > > > >
