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Benedict commented on CASSANDRA-7546:
-------------------------------------
Yes, I'm referring to the memtables - an AtomicSortedColumns instance lives
until its containing memtable is flushed. 100MB/s is around 1M snaptree node
allocations, so that is maybe a little high for deciding there's too much
competition (although with ~ 1000 items present this is only 100k inserts), so
how about we fix it to 10MB/s, to be exceeded by 10Mb. We could certainly hit
100MB of waste, no trouble (under high competition we'll see orders of
magnitude more wasted than used, and memtables usually store 1Gb+), but I think
it's better to trigger a little more readily
> 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_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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