Uploaded image for project: 'Core Server'
  1. Core Server
  2. SERVER-5032

unnecessarily large nScanned occurs during sharded $in queries with sort() and limit()

    • Type: Icon: Improvement Improvement
    • Resolution: Duplicate
    • Priority: Icon: Minor - P4 Minor - P4
    • None
    • Affects Version/s: 1.8.2
    • Component/s: Querying
    • None

      A large number of nScannedObjects occurs when a sharded $in query contains both a limit() and sort() clause.

      For example, we have a checkins collection which is sharded by

      {uid: 1}

      and contains the index

      {uid: 1, _id: -1}

      . A db.checkins.find({uid: {$in: [400438]}}).limit(2).sort({_id: -1}) will scan just the two documents returned. db.checkins.find({uid: {$in: [400438, 32]}}).limit(2).sort({_id: -1}) will scan thousands of documents.

      The attachment walks through the example with an interactive console.

            Assignee:
            Unassigned Unassigned
            Reporter:
            davidwas David Wasserstrum
            Votes:
            0 Vote for this issue
            Watchers:
            0 Start watching this issue

              Created:
              Updated:
              Resolved: