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From "Marcus Eriksson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6621) STCS fallback is not optimal when bootstrapping
Date Thu, 12 Jun 2014 13:47:02 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6621?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14029149#comment-14029149
] 

Marcus Eriksson commented on CASSANDRA-6621:
--------------------------------------------

bq. Stream stables from the source by sorting them by level which will cause streaming of
stables in following order L1 to Lx and then finally L0.
Would it be simpler to just look at all sstables on the new node after we have bootstrapped
(but before we start compacting) and try to "optimally" distribute them in levels? Feels like
we could do a better job in this case

btw, we need the "pick high level sstable for lower level compaction"-thing (or something
similar) after we have run "nodetool cleanup" on a node, we would have the same situation
with many half-empty levels there as well

> STCS fallback is not optimal when bootstrapping
> -----------------------------------------------
>
>                 Key: CASSANDRA-6621
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6621
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Bartłomiej Romański
>            Priority: Minor
>
> The initial discussion started in (closed) CASSANDRA-5371. I've rewritten my last comment
here...
> After streaming (e.g. during boostrap) Cassandra places all sstables at L0. At the end
of the process we end up with huge number of sstables at the lowest level. 
> Currently, Cassandra falls back to STCS until the number of sstables at L0 reaches the
reasonable level (32 or something).
> I'm not sure if falling back to STCS is the best way to handle this particular situation.
I've read the comment in the code and I'm aware why it is a good thing to do if we have to
many sstables at L0 as a result of too many random inserts. We have a lot of sstables, each
of them covers the whole ring, there's simply no better option.
> However, after the bootstrap situation looks a bit different. The loaded sstables already
have very small ranges! We just have to tidy up a bit and everything should be OK. STCS ignores
that completely and after a while we have a bit less sstables but each of them covers the
whole ring instead of just a small part. I believe that in that case letting LCS do the job
is a better option that allowing STCS mix everything up before.
> Is there a way to disable STCS fallback? I'd like to test that scenario in practice during
our next bootstrap...
> Does Cassandra really have to put streamed sstables at L0? The only thing we have to
assure is that sstables at any given level do not overlap. If we stream different regions
from different nodes how can we get any overlaps?



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