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Type: Bug
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Resolution: Duplicate
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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
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ALL
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QO 2022-10-31, QO 2022-11-14, QO 2022-11-28, QO 2022-12-12, QO 2022-12-26, QO 2023-01-09
The cause of the linked BF is that the given query is ambiguous - it asks for a field from $obj and then modifies obj in the same $project:
db.coll.aggregate( [{$project: {"time": "$obj.date", "obj": {$unsetField: {field: "text", input: {k: "text2", v: "$tag.assistant"}}}}}, {$sort: {_id: 1}}, {$limit: 20}] )
As a result, without optimization, $obj.date is missing; but with optimization, $addFields is added before $_internalUnpackBucket as part of stage reordering, resulting in $obj.date returning a value.
After discussing with Chris and Katya, both confirmed that we should make the output match the output of the non-optimized case. Alberto's suggestion for achieving this was that the optimization that moves $addFields before $internalUnpackBucket should be using an internal name rather than "obj", like:
"$addFields:" ( "kInternalName1" : { ...
- related to
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SERVER-66570 Timeseries pushes down metaField-projections that can change semantics
- Closed