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Type: Improvement
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Resolution: Unresolved
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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: Querying
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Query Execution
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(copied to CRM)
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0
Tested with WiredTiger which seems to exhibit this more than MMAP.
Covered index query which has to return all the documents from a collection is slower than just a full collection scan even in cases where index is quite small and collection is very large.
Looking at where we spend time, it appears for each "document" we need to "synthesize" from the index we allocate and free some memory. We apparently have some optimization for avoiding that in collection scan but not full index scan. This is to track the same optimization for index scan.
- causes
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SERVER-59341 Query planner choses collscan over covered index scan for huge collection
- Backlog
- is depended on by
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SERVER-69257 COUNT_SCAN plan not selected when unfiltered $group + $sum on _id performed
- Blocked
- is duplicated by
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SERVER-44057 Find on non-indexed and sort on indexed is slower then find on non-indexed and sort on non-indexed
- Closed
- is related to
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SERVER-29227 $nin operation choose IXSCAN but not COLLSCAN stag
- Closed
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SERVER-20066 Query planner should consider index scans on empty query predicates
- Closed