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https://issues.apache.org/jira/browse/CASSANDRA-16201?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17210234#comment-17210234
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Marcus Eriksson commented on CASSANDRA-16201:
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[~tsteinmaurer] you sure you don't see this in 3.11? looks like we ignore
{{initialCapacity}} in 3.0 here:
https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/utils/btree/BTree.java#L752
but not in 3.11:
https://github.com/apache/cassandra/blob/cassandra-3.11/src/java/org/apache/cassandra/utils/btree/BTree.java#L777
> Cassandra 4.0 b2 - OOM / memory pressure due to object array pre-allocations
> in BatchUpdatesCollector
> -----------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-16201
> URL: https://issues.apache.org/jira/browse/CASSANDRA-16201
> Project: Cassandra
> Issue Type: Bug
> Reporter: Thomas Steinmaurer
> Priority: Normal
> Attachments: screenshot-1.png
>
>
> In a Cas 2.1 / 3.0 / 3.11 / 4.0b2 comparison test with the same load profile,
> we see 4.0b2 going OOM from time to time. According to a heap dump, we have
> multiple NTR threads in a 3-digit MB range.
> This is likely related to object array pre-allocations at the size of
> {{BatchUpdatesCollector.updatedRows}} per {{BTree}} although there is always
> only 1 {{BTreeRow}} in the {{BTree}}.
> !screenshot-1.png!
> So it seems we have many, many 20K elemnts pre-allocated object arrays
> resulting in a shallow heap of 80K each, although there is only one element
> in the array.
> This sort of pre-allocation is causing a lot of memory pressure.
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