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  1. Core Server
  2. SERVER-19178

In WiredTiger capped collection truncates, avoid walking lists of deleted items

    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: 3.0.4
    • Fix Version/s: 3.0.5
    • Component/s: WiredTiger
    • Labels:
      None
    • Backwards Compatibility:
      Fully Compatible

      Description

      Issue Status as of Jul 14, 2015

      ISSUE SUMMARY
      Capped collection handling in WiredTiger is inefficient because of way that WiredTiger tracks and expires documents in the capped collection.

      WiredTiger uses a specific internal cursor to find the "beginning of the capped collection". Combined with asynchronous deletion of expired capped collection records, this is inefficient for collections with high numbers of inserts because requests have to process large number of expired documents.

      USER IMPACT
      Capped collection performance degrades over time. Note that the oplog is a capped collection, so users running replica sets with WiredTiger may be impacted by this issue even if no other capped collections are used.

      RESOLUTION DETAILS
      WiredTiger now caches the current "first" unexpired document in a capped collection. This change improves performance for all capped collections, but is particular important for the performance of replication because the oplog depends on capped collection performance.

      AFFECTED VERSIONS
      MongoDB 3.0.0 through 3.0.4.

      FIX VERSION
      The fix is included in the 3.0.5 production release.

      Original description

      Backport part of SERVER-18875 to MongoDB 3.0 to address the most serious performance issues with long-running workloads using capped collections.

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                  Updated:
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