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From "Stefan Podkowinski (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12730) Thousands of empty SSTables created during repair - TMOF death
Date Tue, 08 Nov 2016 09:41:59 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15647047#comment-15647047
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Stefan Podkowinski commented on CASSANDRA-12730:
------------------------------------------------

Stream sessions should only be created at the end of the repair process and only one for each
host destination. I'm therefor a bit skeptical if the proposed optimization would make that
much of a difference. I'd expect that the higher number of sstables are actually the result
of the streaming session itself, where the node would receive lot's of sstables for mismatching
token ranges from it's replica peers. You should be able to validate this by comparing the
number of sstable flushes (aka switch count) with the total number of sstables (as in your
provided graphs).

It would also be helpful if you could summarize relevant settings, such as vnodes, repair
parallelism, incremental repair usage, DCs and RF, ..


> Thousands of empty SSTables created during repair - TMOF death
> --------------------------------------------------------------
>
>                 Key: CASSANDRA-12730
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12730
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Local Write-Read Paths
>            Reporter: Benjamin Roth
>            Priority: Critical
>
> Last night I ran a repair on a keyspace with 7 tables and 4 MVs each containing a few
hundret million records. After a few hours a node died because of "too many open files".
> Normally one would just raise the limit, but: We already set this to 100k. The problem
was that the repair created roughly over 100k SSTables for a certain MV. The strange thing
is that these SSTables had almost no data (like 53bytes, 90bytes, ...). Some of them (<5%)
had a few 100 KB, very few (<1% had normal sizes like >= few MB). I could understand,
that SSTables queue up as they are flushed and not compacted in time but then they should
have at least a few MB (depending on config and avail mem), right?
> Of course then the node runs out of FDs and I guess it is not a good idea to raise the
limit even higher as I expect that this would just create even more empty SSTables before
dying at last.
> Only 1 CF (MV) was affected. All other CFs (also MVs) behave sanely. Empty SSTables have
been created equally over time. 100-150 every minute. Among the empty SSTables there are also
Tables that look normal like having few MBs.
> I didn't see any errors or exceptions in the logs until TMOF occured. Just tons of streams
due to the repair (which I actually run over cs-reaper as subrange, full repairs).
> After having restarted that node (and no more repair running), the number of SSTables
went down again as they are compacted away slowly.
> According to [~zznate] this issue may relate to CASSANDRA-10342 + CASSANDRA-8641



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