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Type:
Improvement
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Resolution: Unresolved
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: None
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None
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Query Optimization
I was working with cheahuychou.mao@mongodb.com to investigate some ways to improve performance of an internal sharding query and we noticed that the first of these two generates a covered plan, and the second does not:
{"$project": {"_id": 0, "key": {"$meta": "indexKey"}}},
{
"$group": {
"_id": {"key0": {"$getField": {"field": "a.y.ii", "input": "$key"}}},
"frequency": {"$sum": 1}
}
},
{
"$group": {
"_id": {
"$let": {vars: {key: {"$meta": "indexKey"}},
"in": {
"key0": {"$getField": {"field": "a.y.ii", "input": "$$key"}}}
}
},
"frequency": {"$sum": 1}
}
},
Explains are attached.
- related to
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SERVER-78105 Optimize the aggregation pipeline used by analyzeShardKey command to calculate cardinality and frequency
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- Closed
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