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From "Vusal Ahmadoglu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12961) LCS needlessly checks for L0 STCS candidates multiple times
Date Tue, 03 Oct 2017 11:20:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16189558#comment-16189558
] 

Vusal Ahmadoglu commented on CASSANDRA-12961:
---------------------------------------------

Thanks [~jjirsa]. That's a good news!

> LCS needlessly checks for L0 STCS candidates multiple times
> -----------------------------------------------------------
>
>                 Key: CASSANDRA-12961
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12961
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Compaction
>            Reporter: Jeff Jirsa
>            Assignee: Vusal Ahmadoglu
>            Priority: Trivial
>              Labels: lhf
>             Fix For: 4.0
>
>         Attachments: 0001-CASSANDRA-12961-Moving-getSTCSInL0CompactionCandidat.patch
>
>
> It's very likely that the check for L0 STCS candidates (if L0 is falling behind) can
be moved outside of the loop, or at very least made so that it's not called on each loop iteration:
> {code}
>         for (int i = generations.length - 1; i > 0; i--)
>         {
>             List<SSTableReader> sstables = getLevel(i);
>             if (sstables.isEmpty())
>                 continue; // mostly this just avoids polluting the debug log with zero
scores
>             // we want to calculate score excluding compacting ones
>             Set<SSTableReader> sstablesInLevel = Sets.newHashSet(sstables);
>             Set<SSTableReader> remaining = Sets.difference(sstablesInLevel, cfs.getTracker().getCompacting());
>             double score = (double) SSTableReader.getTotalBytes(remaining) / (double)maxBytesForLevel(i,
maxSSTableSizeInBytes);
>             logger.trace("Compaction score for level {} is {}", i, score);
>             if (score > 1.001)
>             {
>                 // before proceeding with a higher level, let's see if L0 is far enough
behind to warrant STCS
>                 CompactionCandidate l0Compaction = getSTCSInL0CompactionCandidate();
>                 if (l0Compaction != null)
>                     return l0Compaction;
> ......
> {code}



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