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Date: Tue, 26 Sep 2017 22:03:00 +0000 (UTC)
From: "Vusal Ahmadoglu (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.13023623.1480304188000.209553.1506463380450@Atlassian.JIRA>
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Subject: [jira] [Commented] (CASSANDRA-12961) LCS needlessly checks for L0
 STCS candidates multiple times
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archived-at: Tue, 26 Sep 2017 22:03:04 -0000


    [ https://issues.apache.org/jira/browse/CASSANDRA-12961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16181654#comment-16181654 ] 

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

Hi Jeff. I checked your last circlleci tests. I got the same failure ([circleci|https://circleci.com/gh/vusal-ahmadoglu/cassandra/10]): _org.apache.cassandra.streaming.StreamTransferTaskTest Tests run: 2, Failures: 1_

> 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.x
>
>         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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