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  1. Core Server
  2. SERVER-16921

WT oplog bottleneck on secondary

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    • Type: Icon: Bug Bug
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • 3.0.0-rc7
    • Affects Version/s: 2.8.0-rc5
    • Component/s: Replication, WiredTiger
    • None
    • Fully Compatible
    • ALL

      We converted one secondary to 2.8.0-rc5 at approximately 16:00 UTC on 2015-01-016. The throughput observed during the "oplog catch-up" phases of the initial sync was truly impressive!

      The secondary continued to perform as expected until 2015-01-17 at approximately 11:00 UTC. At this point it seems that the throughput of the secondary dropped enough that it can no longer keep up with the 2.6.5 primary. The replication lag is increasing steadily, but in a linear fashion. Thus, the throughput dropped to X% of the primary load, but that X% has been holding steady since 11:00 - X does not seem to be decreasing.

      There is nothing obvious in the logs (will attach anyway) other than a gradual increase in the frequency of "serverStatus was very slow" messages. serverStatus appears to be slow in the oplog phase. (Presumably, this is symptom, not cause, but mentioning anyway).

            0       0       0
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T04" | wc
      0       0       0
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T05" | wc
      0       0       0
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T06" | wc
      0       0       0
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T07" | wc
      1      61     421
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T08" | wc
      3     183    1266
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T09" | wc
     12     732    5076
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T10" | wc
     53    3233   22402
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T11" | wc
    147    8967   62167
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T12" | wc
    154    9394   65086
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T13" | wc
    151    9211   63832
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T14" | wc
    142    8662   60027
[cnelson@mms-db-1.ny1 /var/log/mongod-mmsconfig1-prod]$ grep "was very slow" mongod.log | grep "2015-01-17T15" | wc

        1. capped_as_neeed.png
          122 kB
          Daniel Pasette
        2. capped_truncate_parallel.js
          0.8 kB
          Daniel Pasette
        3. capped_truncate.js
          1 kB
          Daniel Pasette
        4. mmsconfig1.png
          313 kB
          Cailin Nelson
        5. mmsconfig1-2015-01-18.png
          365 kB
          Cailin Nelson
        6. mms-db-1.ny1.10gen.cc-snapshot.png
          123 kB
          Daniel Pasette
        7. mms-db-1.ny1-small-oplog.png
          87 kB
          Cailin Nelson
        8. mms-db-1-repl-progress.png
          79 kB
          Daniel Pasette
        9. pri.png
          310 kB
          Bruce Lucas
        10. sec.png
          146 kB
          Bruce Lucas

            Assignee:
            eliot Eliot Horowitz (Inactive)
            Reporter:
            cailin.nelson@mongodb.com Cailin Nelson (Inactive)
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            Watchers:
            20 Start watching this issue

              Created:
              Updated:
              Resolved: