Index access stats should be recorded for $match & mapReduce

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      Reproduction case for aggregation:

      db.test.drop();
db.test.save({a: 1});
db.test.ensureIndex({a: 1});
db.test.aggregate([{$match: {a: 1}}]);
var statsArr = db.test.aggregate([{"$indexStats": {}}]).toArray();
for (var idx in statsArr) {
    var doc = statsArr[idx];
    if (doc.name === "a_1") {
        assert(doc.accesses.ops == 1);
    }
}
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      Reproduction case for aggregation: db.test.drop(); db.test.save({a: 1}); db.test.ensureIndex({a: 1}); db.test.aggregate([{$match: {a: 1}}]); var statsArr = db.test.aggregate([{ "$indexStats" : {}}]).toArray(); for ( var idx in statsArr) { var doc = statsArr[idx]; if (doc.name === "a_1" ) { assert (doc.accesses.ops == 1); } }
    • QuInt E (01/11/16), Query F (02/01/16)
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      Index access stats, retrievable via the $indexStats aggregation source, track the number of times a given index was used to satisfy a user operation.

      $match as a document source in aggregation can make use of indexes to retrieve documents but is currently not recording usage statistics. Support should be added for $match as exclusion could lead to the wrong conclusion as to whether an index is being used.

      Also missing is a hook to record index access when a mapReduce uses an index to satisfy a "query" argument. This issue will add support for both aggregation and mapReduce.

            Assignee:
            James Wahlin
            Reporter:
            James Wahlin
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              Created:
              Updated:
              Resolved: