[jira] [Commented] (CASSANDRA-5936) Improve the way we pick L0 compaction candidates

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-5936?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13817818#comment-13817818 ] 

Jonathan Ellis commented on CASSANDRA-5936:
-------------------------------------------

bq. curious why this logic is only? run for L0 compactions

This is actually flush logic, not compaction.  So that makes more sense now.

Created CASSANDRA-6323 for this since it's not the same problem that Marcus is talking about in the description here.

> Improve the way we pick L0 compaction candidates
> ------------------------------------------------
>
>                 Key: CASSANDRA-5936
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5936
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Marcus Eriksson
>            Assignee: Marcus Eriksson
>             Fix For: 2.1
>
>
> We could improve the way we pick compaction candidates in level 0 in LCS.
> The most common way for us to get behind on compaction is after repairs, we should exploit the fact that the streamed sstables are most often very narrow in range since the other nodes in the ring will have a similar sstable-range-distribution. We should in theory be able to do 10 concurrent compactions involving L1 - ie, partition L0 in buckets defined by the sstables in L1 to only keep one L1 SSTable busy for every compaction (be it L1 to L2 or L0 to L1).
> we will need some heuristics on when to select candidates from the buckets and when to do it the old way (since L0 sstables can span several L1 sstables)



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