Major - P3 Description
Repro with this script:
var t = db.t;
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t.drop();
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t.ensureIndex({"shortId": 1});
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t.ensureIndex({"a.b.startDate": 1});
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t.ensureIndex({"a.b.endDate": 1});
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// Make _startDate and _endDate indices multikey.
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t.save({a: [{b: {startDate: new Date(), endDate: new Date()}},
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{b: {startDate: new Date(), endDate: new Date()}}]});
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t.find({"shortId": "aj72u4",
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_sites: { $in: [ "foo", "bar" ] },
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_allNamespaces: { $in: [ "1", "2", "3", "4" ] },
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"a.b": { $elemMatch: { startDate: { $lte: new Date(1388462400000) },
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endDate: { $gt: new Date(1388462400000) },
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_r: { $in: [ BinData(0,true) ] },
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_p: { $in: [ BinData(0,true), BinData(0,true) ] },
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_o: { $in: [ BinData(0,true) ] } } }
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}).itcount();
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The sixth and final indexed solution generated by the planner should have one index scan over "startDate" and one index scan over "endDate". Instead, both child index scans are over "startDate":
------------AND_HASH
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---------------fetched = 0
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---------------sortedByDiskLoc = 0
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---------------getSort = [{ a.b.startDate: 1 }, ]
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---------------Child 0:
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---------------IXSCAN
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------------------keyPattern = { a.b.startDate: 1.0 }
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------------------direction = 1
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------------------bounds = field #0['a.b.startDate']: (true, new Date(1388462400000)]
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------------------fetched = 0
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------------------sortedByDiskLoc = 0
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------------------getSort = [{ a.b.startDate: 1 }, ]
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---------------Child 1:
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---------------IXSCAN
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------------------keyPattern = { a.b.startDate: 1.0 }
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------------------direction = 1
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------------------bounds = field #0['a.b.startDate']: (new Date(1388462400000), new Date(9223372036854775807)]
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------------------fetched = 0
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------------------sortedByDiskLoc = 0
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------------------getSort = [{ a.b.startDate: 1 }, ]
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