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From "sankalp kohli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6621) STCS fallback is not optimal when bootstrapping
Date Tue, 10 Jun 2014 21:13:03 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6621?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14027029#comment-14027029
] 

sankalp kohli commented on CASSANDRA-6621:
------------------------------------------

"If we stream different regions from different nodes how can we get any overlaps?"
If a node from which it is streaming has the same row in two stable in different levels, it
will come in as 2 stables. The only place we can put it is L0. 
We might want to also stream the stable level and can put stables coming from same level in
one level on the bootstrapping node.  The problem with this will be that we might end up with
very few stable in higher levels violating the constrain that only last level can be less
than limit. 


> 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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