will UseCompressedOops be useful? for application using less than 4GB memory, it will be better that 64bit reference. But for larger memory using application, it will not be cache friendly. "JRocket the definite guide" says: "Naturally, 64 GB isn't a theoretical limit but just an example. It was mentioned because compressed references on 64-GB heaps have proven beneficial compared to full 64-bit pointers in some benchmarks and applications. What really matters, is how many bits can be spared and the performance benefit of this approach. In some cases, it might just be easier to use full length 64-bit pointers."
2011/3/18 Dyer, James <james.d...@ingrambook.com>: > We're on the final stretch in getting our product database in Production with > Solr. We have 13m "wide-ish" records with quite a few stored fields in a > single index (no shards). We sort on at least a dozen fields and facet on > 20-30. One thing that came up in QA testing is we were getting full gc's due > to "promotion failed" conditions. This led us to believe we were dealing > with large objects being created and a fragmented old generation. After > improving, but not solving, the problem by tweaking "conventional" jvm > parameters, our JVM expert learned about some newer tuning params included in > Sun/Oracle's JDK 1.6.0_24 (we're running RHEL x64, but I think these are > available on other platforms too): > > These 3 options dramatically reduced the # objects getting promoted into the > Old Gen, reducing fragmentation and CMS frequency & time: > -XX:+UseStringCache > -XX:+OptimizeStringConcat > -XX:+UseCompressedStrings > > This uses compressed pointers on a 64-bit JVM, significantly reducing the > memory & performance penalty in using a 64-bit jvm over 32-bit. This reduced > our new GC (ParNew) time significantly: > -XX:+UseCompressedOops > > The default for this was causing CMS to begin too late sometimes. (the > documentated 68% proved false in our case. We figured it was defaulting > close to 90%) Much lower than 75%, though, and CMS ran far too often: > -XX:CMSInitiatingOccupancyFraction=75 > > This made the "stop-the-world" pauses during CMS much shorter: > -XX:+CMSParallelRemarkEnabled > > We use these in conjunction with CMS/ParNew and a 22gb heap (64gb total on > the box), with a 1.2G newSize/maxNewSize. > > In case anyone else is having similar issues, we thought we would share our > experience with these newer options. > > James Dyer > E-Commerce Systems > Ingram Content Group > (615) 213-4311 > >
