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Type:
Improvement
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Resolution: Done
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Priority:
Major - P3
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Affects Version/s: 3.3.9
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Component/s: Aggregation Framework
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Query Optimization
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Fully Compatible
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Query 2017-03-27, Query 2017-04-17, QO 2023-03-20
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151
Aggregation pipeline sends down to query fields to return which are generated later in the pipeline (as result of "as" in $lookup).
Reproduce:
db.companies.explain().aggregate({$match:{_id:"14"}},{$graphLookup:{from:"companies",startWith:"$_id",connectFromField:"_id",connectToField:"parent",as:"tree",maxDepth:5, depthField:"order"}},{$group:{"_id":"$tree.country"}})
{
"waitedMS" : NumberLong(0),
"stages" : [
{
"$cursor" : {
"query" : {
"_id" : "14"
},
"fields" : {
"tree.country" : 1,
"_id" : 1
},
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "d.companies",
"indexFilterSet" : false,
"parsedQuery" : {
"_id" : {
"$eq" : "14"
}
},
"winningPlan" : {
"stage" : "PROJECTION",
"transformBy" : {
"tree.country" : 1,
"_id" : 1
},
"inputStage" : {
"stage" : "IDHACK"
}
},
"rejectedPlans" : [ ]
}
}
},
{
"$graphLookup" : {
"from" : "companies",
"as" : "tree",
"connectToField" : "parent",
"connectFromField" : "_id",
"startWith" : "$_id",
"depthField" : "order",
"maxDepth" : NumberLong(5)
}
},
{
"$group" : {
"_id" : "$tree.country"
}
}
],
"ok" : 1
}
Note "tree.country" which is coming from the lookup and not original document.
It appears that if project or group needs a field after lookup, there is no filtering out of fields that start with string passed as "as:" to $lookup and it ends up being pushed down into the query.
- is related to
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SERVER-72020 [CQF] Make sure computed fields are not redundantly pulled from storage
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- Closed
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- Backlog
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