Include merge sort in sharded aggregation explain output

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    • Type: Improvement
    • Resolution: Fixed
    • Priority: Major - P3
    • 5.3.0
    • Affects Version/s: None
    • Component/s: None
    • None
    • Minor Change
    • 135
    • None
    • 3
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      At some point before 4.2 we stopped including the merge sort in the explain output - I believe because the merge sort started happening within the $mergeCursors, which is not created nor displayed in explain output.

      We should somehow enhance the explain output to include the merge sort so that users don't mistakenly conclude that the merged output is not sorted.

       
      4.0:

      splitPipeline: {
  shardsPart: [
    {
      '$match': { mykey: { '$in': [ 0, 1, 3, 7 ] } }
    },
    { '$sort': { sortKey: { favColour: 1 }, limit: 5 } }
  ],
  mergerPart: [
    {
      '$sort': { sortKey: { favColour: 1 }, mergePresorted: true, limit: 5 }
    }
  ]
}

      4.2/4.4:

       
splitPipeline: {
  shardsPart: [
    {
      '$match': { mykey: { '$in': [ 0, 1, 3, 7 ] } }
    },
    { '$sort': { sortKey: { favColour: 1 }, limit: 5 } }
  ],
  mergerPart: [ { '$limit': 5 } ]
}

       

            Assignee:
            Davis Haupt (Inactive)
            Reporter:
            Charlie Swanson
            Votes:
            2 Vote for this issue
            Watchers:
            13 Start watching this issue

              Created:
              Updated:
              Resolved: