G1GC Old generation taking too much time.

[Pravin Sinha]

Hi,

We are facing a weird problem when G1GC enabled.  The Old Gen collections took about 50 min and the process was completely unresponsive.
This is what we have in our deployment:
* Max heap consumption was around 12.5G
* we had set for JVM:
-d64 -Xms15360m -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=9080 -Dcom.sun.management.jmxremote.local.only=false -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -XX:+UseG1GC -XX:MaxGCPauseMillis=200 -XX:GCPauseIntervalMillis=400  -XX:+PrintGCTimeStamps -XX:+PrintGCDetails  -Xloggc:/loc_to_log.

We are running it on a 32 core box and the number of ParellelGC thread is 23 ( I think using 5/8 rule?). Could you please suggest something to try to avoid this long GC time?

Regards,
Pravin
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