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  1. Core Server
  2. SERVER-54890

Disable background validation and dbHash checks on capped collections in 4.4

    • Type: Icon: Improvement Improvement
    • Resolution: Fixed
    • Priority: Icon: Major - P3 Major - P3
    • 4.4.7
    • Affects Version/s: None
    • Component/s: None
    • None
    • Fully Compatible
    • Execution Team 2021-05-17
    • 181

      Capped collections perform un-timestamped writes to delete expired documents, but all documents will have had an assigned timestamp when first inserted. This breaks contracts with the storage engine regarding mixed-use timestamps and means that point-in-time reads do not work correctly on capped collections.

      As a result, background validation and dbHash will fail with the following errors when reading documents that have just been deleted:

      • DataCorruptionDetected: Erroneous index key found with reference to non-existent record id
      • Index with name X has inconsistencies.

      These inconsistencies should be inconsequential because they can only happen when reading documents that have already been deleted.

      We already prohibit the use of readConcern: 'snapshot' and multi-document transactions on capped collections for this reason.

            Assignee:
            gregory.wlodarek@mongodb.com Gregory Wlodarek
            Reporter:
            louis.williams@mongodb.com Louis Williams
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              Created:
              Updated:
              Resolved: