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Posted to commits@cassandra.apache.org by "Brandon Williams (Jira)" <ji...@apache.org> on 2022/05/23 17:25:00 UTC
[jira] [Commented] (CASSANDRA-17655) Prevent JVM Humongous allocations
[ https://issues.apache.org/jira/browse/CASSANDRA-17655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17541062#comment-17541062 ]
Brandon Williams commented on CASSANDRA-17655:
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You probably want to +PrintAdaptiveSizePolicy and generate a flame graph to find the source. I didn't find anything significant in CASSANDRA-17408.
> Prevent JVM Humongous allocations
> ---------------------------------
>
> Key: CASSANDRA-17655
> URL: https://issues.apache.org/jira/browse/CASSANDRA-17655
> Project: Cassandra
> Issue Type: Bug
> Reporter: Brad Schoening
> Priority: Normal
>
> Several articles on Cassandra note that certain workloads, especially large partitions, can cause humongous allocations in Java, which can be reduced, but not always eliminated by increasing RegionSize. RegionSize max is 32MB. Humongous allocations are an undesirable performance issue because new objects get directly allocated in old space.
> Below is a sample message seen in the gc.log
> 2022-05-23T18:46:58.743+0800: 3758624.170: [GC pause (G1 Humongous Allocation) (young) (initial-mark) 3758624.171: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 56725, predicted base time: 39.83 ms, remaining time: 160.17 ms, target pause time: 200.00 ms]
> Instead of users tweaking RegionSize, a better solution would be for Cassandra to limit the size of allocations, or consider moving humongous allocations off heap.
>
> References
> [https://docs.oracle.com/en/java/javase/11/gctuning/garbage-first-g1-garbage-collector1.html#GUID-D74F3CC7-CC9F-45B5-B03D-510AEEAC2DAC]
> [https://stevenlacerda.medium.com/identifying-and-fixing-humongous-allocations-in-cassandra-bf46444cec41]
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