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  1. Cassandra
  2. CASSANDRA-8371

DateTieredCompactionStrategy is always compacting

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    • Bug
    • Status: Resolved
    • Normal
    • Resolution: Duplicate
    • None
    • None
    • Normal

    Description

      Running 2.0.11 and having switched a table to DTCS we've seen that disk IO and gc count increase, along with the number of reads happening in the "compaction" hump of cfhistograms.

      Data, and generally performance, looks good, but compactions are always happening, and pending compactions are building up.

      The schema for this is

      CREATE TABLE search (
        loginid text,
        searchid timeuuid,
        description text,
        searchkey text,
        searchurl text,
        PRIMARY KEY ((loginid), searchid)
      );

      We're sitting on about 82G (per replica) across 6 nodes in 4 DCs.
      CQL executed against this keyspace, and traffic patterns, can be seen in slides 7+8 of https://prezi.com/b9-aj6p2esft/

      Attached are sstables-per-read and read-latency graphs from cfhistograms, and screenshots of our munin graphs as we have gone from STCS, to LCS (week ~44), to DTCS (week ~46).

      These screenshots are also found in the prezi on slides 9-11.

      pmcfadin, Bj0rn,

      Can this be a consequence of occasional deleted rows, as is described under (3) in the description of CASSANDRA-6602 ?

      Attachments

        1. sstables.png
          59 kB
          Michael Semb Wever
        2. read-latency.png
          76 kB
          Michael Semb Wever
        3. vg2_iad-month.png
          28 kB
          Michael Semb Wever
        4. java_gc_counts_rate-month.png
          23 kB
          Michael Semb Wever
        5. read-latency-recommenders-adview.png
          57 kB
          Michael Semb Wever
        6. sstables-recommenders-adviews.png
          41 kB
          Michael Semb Wever

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              Bj0rn Björn Hegerfors
              mck Michael Semb Wever
              Björn Hegerfors
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                Updated:
                Resolved: