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From "graham sanderson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7546) AtomicSortedColumns.addAllWithSizeDelta has a spin loop that allocates memory
Date Mon, 28 Jul 2014 22:45:38 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14077057#comment-14077057
] 

graham sanderson commented on CASSANDRA-7546:
---------------------------------------------

Ok, thank you... yeah my only reason for recording something in the actual codebase was to
indicate that to the user that they had ultra heavy partition contention that might be detrimental
to performance, and they should perhaps review their schema. Given that this may not be the
case at all in 3.0 (i.e. it may be gracefully handled in all cases), I'll try out locally
with a WARN statement instead. I'll probably do it at memtable flush anyway which has more
useful context (e.g. the CF in question), and would be less spam-y (i.e. one warn with the
number of contended partitions, though perhaps the contended key(s) are interesting at a lower
log level)... whether we include such logging in the final patch I don't know.

> 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_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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