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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7546) AtomicSortedColumns.addAllWithSizeDelta has a spin loop that allocates memory
Date Thu, 18 Sep 2014 19:04:34 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14139341#comment-14139341
] 

Benedict commented on CASSANDRA-7546:
-------------------------------------

I've uploaded a patch [here|https://github.com/belliottsmith/cassandra/tree/7964-simultinserts],
and another [here|https://github.com/belliottsmith/cassandra/tree/7964+7926] which combines
it with another stress patch that reduces the risk of OOM (although this risk is pretty low,
and almost certainly not what you were hitting) - but as you scale thread count up it becomes
more of a risk

The main 7964 patch includes a couple of small bug fixes as well, and I've tested it against
your schema and some other related schemas that are trickier to process.

One thing I would suggest considering is expanding the clustering column count to increase
the speed of generation, as 1200 items is still quite a few to create for only sending 1 item,
which might end up reducing contention server side. Possibly reduce to only 30-40 items per
tier.

> 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
>             Fix For: 2.1.1
>
>         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_7.txt, 7546.20_7b.txt, 7546.20_alt.txt, 7546.20_async.txt, 7546.21_v1.txt,
hint_spikes.png, suggestion1.txt, suggestion1_21.txt, young_gen_gc.png
>
>
> 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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