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Type: Bug
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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: Aggregation Framework
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None
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Fully Compatible
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ALL
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v4.2
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Query 2020-04-20, Query 2020-05-04
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50
In SERVER-43860, we fixed the behaviour of $merge in the case where we have {whenMatched: pipeline} and {whenNotMatched: insert}. For upgrade/downgrade purposes, we made this new behaviour conditional on the presence of a flag, useNewUpsert, which is set by 4.4 mongoS on aggregations that are sent to the shards. We then backported this fix to 4.2.2.
However, in cases where a $merge is sent to a shard as part of a $mergeCursors pipeline, the 'useNewUpsert' flag is not set on the command. In these scenarios, the old incorrect behaviour is still observed.
- is related to
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SERVER-43860 Pipeline style update in $merge can produce unexpected result
- Closed