[jira] [Commented] (CASSANDRA-12730) Thousands of empty SSTables created during repair - TMOF death

["Benjamin Roth (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-12730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15639264#comment-15639264 ] 

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

It happened again during a repair over night: https://cl.ly/1g0h2p370D04
Same symptoms: Tens of thousands of (nearly) empty SSTables have been created. I guess the reason is, that there happened a lot of streaming during the repair as the cluster ran into trouble when I added a new node recently which again did not work quite as it should have.

Is it REALLY intended behaviour or necessary, that a flush has to occur before EVERY stream session? If there are a lot of streams for a lot of small partitions, this can (and does) kill a node. Of course, e.g. in reaper you can lower the repair intensity but IMHO this behaviour is dangerous and to me it rather looks like a design flaw than a problem a devop should have to deal with.

> 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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