cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Benjamin Roth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12730) Thousands of empty SSTables created during repair - TMOF death
Date Tue, 08 Nov 2016 07:50:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15646815#comment-15646815
] 

Benjamin Roth commented on CASSANDRA-12730:
-------------------------------------------

Good point. I also encountered situations where repairs behaved not as expected (e.g. see
CASSANDRA-12489). Unfortunately I did not have the time yet to investigate more on that.

But for that very case we run into recently, I guess this "harmless optimization" could help
the server to survive that situation without crashing. The cause that crashed the server was
not that there were a lot of streams (which in this case were probably in deed necessary)
but that there were more than 100k open files which could have been easily avoided if the
flushes wouldn't have created tens of thousands nearly empty SSTables.

So why not optimize the one situation and investigate on the other?


> 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



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

Mime
View raw message