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  1. Core Server
  2. SERVER-17183

Btree depth for oplog grows faster than expected

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: 3.0.0-rc7
    • Fix Version/s: 3.0.0-rc9, 3.1.0
    • Component/s: WiredTiger
    • Labels:
      None
    • Backwards Compatibility:
      Fully Compatible
    • Operating System:
      ALL
    • Backport Completed:

      Description

      While doing perf testing of an insert only workload, I noticed that the oplog collection's btree was deepening faster than expected. After only ~1 minute, the tree depth grows to 4 and after ~2 minutes it grows to 5.

      I'm not sure this is a problem per se, but seems abnormal.

      I couldn't seem to reproduce this with an oplog size of 1GB or 3GB, but happens very quickly with 5GB. Tested with rc7 and latest master (git hash: e4c60053b2967e16f765fa25d16aa6d629faa196)

      Running mongodb with --master and --oplogSize 5000:

      ./mongod --dbpath /home/dan/wt-data/ --storageEngine wiredTiger --master --oplogSize 5000

      Run workload:

      mongo deep_tree.js

      Tracking the btree depth here:

      > use local
      switched to db local
      > while(1) {print(""+ Date()+" " + db.oplog.$main.stats().wiredTiger.btree['maximum tree depth']);sleep(5000)}
      Wed Feb 04 2015 15:32:58 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:32:59 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:00 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:05 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:10 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:15 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:20 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:25 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:30 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:35 GMT-0500 (EST) 3
      Wed Feb 04 2015 15:33:40 GMT-0500 (EST) 4
      .
      .
      .
      Wed Feb 04 2015 15:34:37 GMT-0500 (EST) 5

      Workload generated using dead simple insertion of identical 565 byte docs.

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            Assignee:
            keith.bostic Keith Bostic
            Reporter:
            pasette Daniel Pasette
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              Dates

              Created:
              Updated:
              Resolved: