[
https://issues.apache.org/jira/browse/CASSANDRA-7546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14072530#comment-14072530
]
graham sanderson commented on CASSANDRA-7546:
---------------------------------------------
Good point - I was mixing the two types of memory allocation in my head... that
said I don't know when we are seeing this in production how long each
AtomicSortedColumns instance lives.
bq. they stick around until they fill up
I assume you are referring to the memtables there... what defines "full"
besides.
- there is a hard(ish) memory limit in yaml
- MeteredFlusher flushes high traffic stuff
Basically, I'm just checking that we don't think our 100MB/s wastage may never
trigger due to aggressive flushing... theoretically we must be wasting MUCH
more than we are really writing, but I don't have numbers (I could look at the
logs to get them) to see how often hints memtables were being flushed during
this process and how big they were.
> 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.
--
This message was sent by Atlassian JIRA
(v6.2#6252)
