[ES v2.3] jvm keep gc with no index and query, slow down whole cluster

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we have a huge cluster. 5 nodes.
about 15000000000 documents
and 15000 shards.

jvm:
ES_JAVA_OPTS="-XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=100 -XX:GCLogFileSize=10M -XX:+CMSIncrementalMode -XX:+CMSScavengeBeforeRemark -XX:+ParallelRefProcEnabled -XX:NewSize=5G -XX:MaxTenuringThreshold=15 -XX:SurvivorRatio=20 -XX:CMSInitiatingOccupancyFraction=50 -XX:+UseCMSInitiatingOccupancyOnly"

it keeps gc, looks like figure below

48 AM
Screen Shot 2018-01-08 at 10.56.48 AM.png3360Ă—2100 1.88 MB

after delete half data, reduce both shards count and ducuments size. it becomes health.
I am querying what is the root cause? is there any limit for shards count or index size on a node.

what metadata maintained in memory, cause occupy huge memory when cluster goes huge.

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Too many shards per node seems to me one of the good reasons. Then it can be caused by fielddata as well. Depends on your mapping and if you are using doc values or not.

Also, you should upgrade.

But the first thing to do is to reduce the number of shards per node.

Have a look at

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