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  1. Cassandra
  2. CASSANDRA-4316

Compaction Throttle too bursty with large rows

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Details

    • Improvement
    • Status: Resolved
    • Normal
    • Resolution: Fixed
    • 1.2.5
    • None

    Description

      In org.apache.cassandra.db.compaction.CompactionIterable the check for compaction throttling occurs once every 1000 rows. In our workload this is much too large as we have many large rows (16 - 100 MB).

      With a 100 MB row, about 100 GB is read (and possibly written) before the compaction throttle sleeps. This causes bursts of essentially unthrottled compaction IO followed by a long sleep which yields inconsistence performance and high error rates during the bursts.

      We applied a workaround to check throttle every row which solved our performance and error issues:

      line 116 in org.apache.cassandra.db.compaction.CompactionIterable:
      if ((row++ % 1000) == 0)
      replaced with
      if ((row++ % 1) == 0)

      I think the better solution is to calculate how often throttle should be checked based on the throttle rate to apply sleeps more consistently. E.g. if 16MB/sec is the limit then check for sleep after every 16MB is read so sleeps are spaced out about every second.

      Attachments

        1. 4316-1.2.txt
          24 kB
          Jonathan Ellis
        2. 4316-v3.txt
          22 kB
          Jonathan Ellis
        3. 4316-1.2-v2.txt
          17 kB
          Yuki Morishita
        4. 4316-1.2.txt
          16 kB
          Yuki Morishita

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          People

            jbellis Jonathan Ellis
            wrl Wayne Lewis
            Jonathan Ellis
            Yuki Morishita
            Ryan McGuire Ryan McGuire
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            Dates

              Created:
              Updated:
              Resolved: