Uploaded image for project: 'Core Server'
  1. Core Server
  2. SERVER-48453

Lazily initialize a record store's auto incrementing counter on deletes

    • Fully Compatible
    • ALL
    • v4.4, v4.2, v4.0
    • Execution Team 2020-06-01, Execution Team 2020-06-15
    • 14

      Apologies for summarizing the solution and not the problem.

      It's imperative that the update chain for a storage engine key goes in increasing timestamp order (with only a few explicit caveats). The lazy initializing of record ids only on inserts creates a scenario where a key can be reused, and in the case of the _mdb_catalog, can result in an update that can't be rolled back (intentional 0-timestamp value) sitting on top of an update that must be eligible for rollback. This sequence of updates "locks in" a non-majority committed update.

      The scenario:

      • Create collection A. Inserts into _mdb_catalog (initializing the counter to "1") with RecordId(1), Timestamp(10)
      • Drop collection A. Timestamp(20)
      • Rollback to 15
      • Replay drop collection A (No more records in the _mdb_catalog)
      • Create a non-replicated collection (e.g: `local.replset.initialsync`). Initialize the counter to "1", Insert Record(1), Timestamp(0)
      • Rollback to 15. The drop at timestamp 20 is "locked in". Collection A is missing

            daniel.gottlieb@mongodb.com Daniel Gottlieb (Inactive)
            daniel.gottlieb@mongodb.com Daniel Gottlieb (Inactive)
            0 Vote for this issue
            5 Start watching this issue