[CASSANDRA-7432] Add new CMS GC flags to cassandra_env.sh for JVM later than 1.7.0_60

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 2.0.10, 2.1.1
• Component/s: Packaging
• Assignee: Brandon Williams Assign to me
• Reporter: graham sanderson

Authors

Brandon Williams

Reviewers

Jonathan Ellis

• Created: 21/Jun/14 16:03
• Updated: 16/Apr/19 09:31
• Resolved: 05/Aug/14 22:55

Description

The new flags in question are as follows:

-XX:+CMSParallelInitialMarkEnabled
-XX:+CMSEdenChunksRecordAlways

Given we already have

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

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)

Issue Links

• is related to: CASSANDRA-7714 Add new CMS GC flags to Windows startup scripts for JVM later than 1.7.0_60