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https://issues.apache.org/jira/browse/CASSANDRA-16201?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17223585#comment-17223585
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Thomas Steinmaurer commented on CASSANDRA-16201:
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{quote}
I will keep that running over the night and provide another set of JFR files
for 3.0, 3.11 and 4.0 with the patch.
{quote}
[~mck], in my provided OneDrive share provided on Oct 12, 2020 to you, there is
now an additional sub-directory called {{_perffixes_jfr_20201027}}, which
contains a new set of JFR files for all versions (including 2.1), with the
patch applied to 3.0, 3.11 and 4.0.
[~marcuse], let me know if/how I could share the new JFR files with you as well.
> Reduce amount of allocations during batch statement execution
> -------------------------------------------------------------
>
> Key: CASSANDRA-16201
> URL: https://issues.apache.org/jira/browse/CASSANDRA-16201
> Project: Cassandra
> Issue Type: Bug
> Components: Local/Other
> Reporter: Thomas Steinmaurer
> Assignee: Marcus Eriksson
> Priority: Normal
> Fix For: 3.0.x, 3.11.x, 4.0-beta
>
> Attachments: screenshot-1.png, screenshot-2.png, screenshot-3.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|width=100%!
> 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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