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Type: Improvement
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Resolution: Fixed
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Priority: Major - P3
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Affects Version/s: None
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Component/s: None
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Labels:None
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Fully Compatible
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QE 2021-10-18
The needsMerge behavior at mongod-side has not been yet implemented. Until it's implemented, we should block $group stage from being pushed down to SBE when needsMerge is requested from the mongos. Otherwise, it may lead to incorrect results for sharded $group, especially for accumulators that need special behavior for finalization steps when needsMerge is requested.
This is just an interim fix until we implement needsMerge behavior, which is done by SERVER-59070.