Count plans sometimes don't need a FETCH

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    • Minor Change
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    • Query 2017-06-19
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      Not sure why this is happening, but given index on username:1 match by username and group on username correctly uses covered index, but grouping on constant does not:

      aggregate { aggregate: "t1", pipeline: [ { $match: { username: /^a/ } }, { $group: { _id: "$username", count: { $sum: 1.0 } } } ], cursor: {} } planSummary: IXSCAN { username: 1.0 } keysExamined:2 docsExamined:0 cursorExhausted:1 numYields:0 nreturned:1
aggregate { aggregate: "t1", pipeline: [ { $match: { username: /^a/ } }, { $group: { _id: 1.0, count: { $sum: 1.0 } } } ], cursor: {} } planSummary: IXSCAN { username: 1.0 } keysExamined:2 docsExamined:1 cursorExhausted:1 numYields:0 nreturned:1

              Assignee:
              Anne Lim (Inactive)
              Reporter:
              Asya Kamsky
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                Created:
                Updated:
                Resolved: