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https://issues.apache.org/jira/browse/CASSANDRA-7546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14087814#comment-14087814
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Benedict commented on CASSANDRA-7546:
-------------------------------------
Well, technically we never ever call addColumn() directly, but in 2.0 we
haven't removed / UnsupportedOperationException'd that path, so I'm not totally
comfortable leaving it as a regular int, as an external call to addColumn would
break it (but then, this probably isn't the end of the world).
However, I actually introduced a double counting bug in changing that :/ ...
and since we don't want to incur the incAndGet every change, and we don't want
to dup code, let's settle for the possible race for maintaining size if
somebody uses the API in a way it isn;t in the codebase right now.
However I think I would prefer to make size final in this case.
> AtomicSortedColumns.addAllWithSizeDelta has a spin loop that allocates memory
> -----------------------------------------------------------------------------
>
> Key: CASSANDRA-7546
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7546
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: graham sanderson
> Assignee: graham sanderson
> Attachments: 7546.20.txt, 7546.20_2.txt, 7546.20_3.txt,
> 7546.20_4.txt, 7546.20_5.txt, 7546.20_6.txt, 7546.20_alt.txt,
> suggestion1.txt, suggestion1_21.txt
>
>
> In order to preserve atomicity, this code attempts to read, clone/update,
> then CAS the state of the partition.
> Under heavy contention for updating a single partition this can cause some
> fairly staggering memory growth (the more cores on your machine the worst it
> gets).
> Whilst many usage patterns don't do highly concurrent updates to the same
> partition, hinting today, does, and in this case wild (order(s) of magnitude
> more than expected) memory allocation rates can be seen (especially when the
> updates being hinted are small updates to different partitions which can
> happen very fast on their own) - see CASSANDRA-7545
> It would be best to eliminate/reduce/limit the spinning memory allocation
> whilst not slowing down the very common un-contended case.
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