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From "Jeff Jirsa (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-12961) LCS needlessly checks for L0 STCS candidates multiple times
Date Sun, 17 Sep 2017 03:41:01 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-12961?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jeff Jirsa updated CASSANDRA-12961:
-----------------------------------
       Reviewer: Jeff Jirsa
    Description: 
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}

  was:

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}


> 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
>
> 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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