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Jonathan Ellis commented on CASSANDRA-7432: ------------------------------------------- More details on what these two patches do: http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2013-May/007374.html (TLDR remark is already parallel but the way it samples the work means that a single thread can be assigned the bulk of the work. CMSEdenChunksRecordAlways fixes this.) +1 from me > Add new CMS GC flags to cassandra_env.sh for JVM later than 1.7.0_60 > -------------------------------------------------------------------- > > Key: CASSANDRA-7432 > URL: https://issues.apache.org/jira/browse/CASSANDRA-7432 > Project: Cassandra > Issue Type: Improvement > Components: Packaging > Reporter: graham sanderson > Assignee: Brandon Williams > Fix For: 1.2.19 > > Attachments: 7432.txt > > > The new flags in question are as follows: > {code} > -XX:+CMSParallelInitialMarkEnabled > -XX:+CMSEdenChunksRecordAlways > {code} > Given we already have > {code} > JVM_OPTS="$JVM_OPTS -XX:+UseParNewGC" > JVM_OPTS="$JVM_OPTS -XX:+UseConcMarkSweepGC" > JVM_OPTS="$JVM_OPTS -XX:+CMSParallelRemarkEnabled" > JVM_OPTS="$JVM_OPTS -XX:+UseTLAB" > if [ "$JVM_ARCH" = "64-Bit" ] ; then > JVM_OPTS="$JVM_OPTS -XX:+UseCondCardMark" > fi > {code} > The assumption would be that people are at least running on large number CPU > cores/threads > I would therefore recommend defaulting these flags if available - the only > two possible downsides for {{+CMSEdenChunksRecordAlways}}: > 1) There is a new very short (probably un-contended) lock in the "slow" (non > TLAB) eden allocation path with {{+CMSEdenChunksRecordAlways}}. I haven't > detected this timing wise - this is the "slow" path after all > 2) If you are running with {{-XX:-UseCMSCompactAtFullCollection}} (not the > default) *and* you call {{System.gc()}} then {{+CMSEdenChunksRecordAlways}} > will expose you to a possible seg fault: (see > [http://bugs.java.com/bugdatabase/view_bug.do?bug_id=8021809]) -- This message was sent by Atlassian JIRA (v6.2#6252)