Uploaded image for project: 'Core Server'
  1. Core Server
  2. SERVER-19593

Allow collscans on $snapshot queries when not using MMAP1

    XMLWordPrintable

Details

    • Improvement
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • 3.0.0
    • 3.1.7
    • Querying
    • None
    • Minor Change
    • Quint Iteration 7

    Description

      In MMAPv1 we need to scan the _id index to ensure we see documents once since records can move in the collection, allowing us to see duplicates or miss documents. In other storage engines this is not allowed, so we should be able to do table scans rather than index scans which can be orders of magnitude slower.

      This would result in a user-facing change since we would no longer be returning documents in _id order, but that is not part of the documented behavior of $snapshot.

      Attachments

        Issue Links

          Activity

            People

              qingyang.chen Qingyang Chen
              mathias@mongodb.com Mathias Stearn
              Votes:
              0 Vote for this issue
              Watchers:
              4 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved: