Details
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Bug
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Resolution: Unresolved
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Major - P3
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None
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None
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None
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Query Execution
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ALL
Description
Based on this community post: https://www.mongodb.com/community/forums/t/clustered-collections-as-lookup-target/246893
The user is worried we are not using clustered index, because in explain output for $lookup they see a lot of collectionScans and no indexes used.
It happens because internally clustered index scan is a collection scan and not an index scan.
We should improve explain output by showing explicitly that clustered index is used.