[jira] [Updated] (CASSANDRA-6621) Add flag to disable STCS in L0

["Jeremiah Jordan (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-6621?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jeremiah Jordan updated CASSANDRA-6621:
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    Summary: Add flag to disable STCS in L0  (was: STCS fallback is not optimal when bootstrapping)

> Add flag to disable STCS in L0
> ------------------------------
>
>                 Key: CASSANDRA-6621
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6621
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Bartłomiej Romański
>            Assignee: Marcus Eriksson
>            Priority: Minor
>              Labels: compaction, streaming
>             Fix For: 2.0.10
>
>         Attachments: 0001-option-to-disallow-L0-stcs.patch, 0001-property-to-disable-stcs-in-l0-v2.patch, 0001-property-to-disable-stcs-in-l0.patch, 0001-wip-keep-sstable-level-when-bootstrapping.patch
>
>
> 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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