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Type:
Task
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Resolution: Unresolved
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Priority:
Major - P3
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Affects Version/s: None
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Labels:
Bounded scans on clustered collections will display a CLUSTERED_IXSCAN stage in the slow query logs and explain output. Clustered collection scans without bounds will continue to display a COLLSCAN.
This only affects the displayed name of the query plan for time-series collections. For example, say I have a time-series collection without any indexes:
db.createCollection('ts', {timeseries: {timeField: 't'}})
If I perform a scan with a filter on time, a CLUSTERED_IXSCAN will be displayed in the explain output:
db.ts.find({t: {$lt: new Date()}).explain()
...
winningPlan: {
stage: 'CLUSTERED_IXSCAN',
filter: {
'$and': [
{
_id: { '$lt': ObjectId("61fcedcd0000000000000000") }
},
{
'control.max.t': {
'$_internalExprLt': ISODate("2022-02-04T10:11:40.610Z")
}
},
{
'control.min.t': {
'$_internalExprLt': ISODate("2022-02-04T09:11:40.610Z")
}
}
]
},
direction: 'forward',
maxRecord: ObjectId("61fcedcd0000000000000000")
},
...
And in the slow query logs:
{"t":{"$date":"2022-02-04T04:14:24.826-05:00"},"s":"I", "c":"COMMAND", "id":51803, "ctx":"conn2","msg":"Slow query","attr":{"type":"command","ns":"test.ts","appName":"mongosh 1.1.9","command":{"find":"ts","filter":{"t":{"$lt":{"$date":"2022-02-04T09:14:24.819Z"}}},"lsid":{"id":{"$uuid":"7d08265d-f56b-4ba5-a35e-578d99fdbe3b"}},"$db":"test"},"planSummary":"CLUSTERED_IXSCAN","resolvedViews":[{"viewNamespace":"test.ts","dependencyChain":["ts","system.buckets.ts"],"resolvedPipeline":[{"$_internalUnpackBucket":{"timeField":"t","bucketMaxSpanSeconds":3600}}]}],"keysExamined":0,"docsExamined":1,"cursorExhausted":true,"numYields":0,"nreturned":9,"queryHash":"8B3F27D2","planCacheKey":"8B3F27D2","queryExecutionEngine":"classic","reslen":420,"locks":{"ParallelBatchWriterMode":{"acquireCount":{"r":1}},"ReplicationStateTransition":{"acquireCount":{"w":1}},"Global":{"acquireCount":{"r":5}},"Database":{"acquireCount":{"r":1}},"Collection":{"acquireCount":{"r":1}},"Mutex":{"acquireCount":{"r":5}}},"storage":{},"remote":"127.0.0.1:53820","protocol":"op_msg","durationMillis":3}}
Description of Linked Ticket
Slow queries on clustered collections report a COLLSCAN, but it's not clear that this is actually a bounded scan over a clustered collection..
Additionally, the explain output reports minRecord and maxRecord, but we should include a flag that specifically indicates that this was a ranged scan over a clustered collection,
- documents
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SERVER-63078 Show when clustered index is used in explain and slow query logs
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- Closed
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