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Mongodb V4.2 has introduced queryHash in slow query logs to identify slow queries with same query shape. While this queryHash is available in slow query logs in mongod logs (shard server), it is not present in any of the slow query logs on my mongos server.

Mongod log

{"t":{"$date":"2021-01-09T01:45:27.821+00:00"},"s":"I",  "c":"COMMAND",  "id":51803,   "ctx":"conn143447","msg":"Slow query","attr":{"type":"command","ns":"xxxx.collection","command":{"find":"collection","filter":{"entityId":"xxxx.ru"},"projection":{"crawlerDataId":0},"sort":{"sourceUpdatedAt":-1},"readConcern":{"provenance":"implicitDefault"},"limit":100,"runtimeConstants":{"localNow":{"$date":"2021-01-09T01:45:27.689Z"},"clusterTime":{"$timestamp":{"t":1610156727,"i":93}}},"_use44SortKeys":true,"shardVersion":[{"$timestamp":{"t":89277,"i":1}},{"$oid":"5cb57c9eafd72c1e06b5c433"}],"clientOperationKey":{"$uuid":"56e5a665-9162-4e1d-a368-165e592d59de"},"lsid":{"id":{"$uuid":"a15a9b9c-bb4f-4d1f-8770-08b64b28ad2b"},"uid":{"$binary":{"base64":"6ikS+z/HSNSwWB1ARioMqqzdlxOaNtFe+gViCoYwELs=","subType":"0"}}},"$clusterTime":{"clusterTime":{"$timestamp":{"t":1610156727,"i":93}},"signature":{"hash":{"$binary":{"base64":"7GLR2+4NQu2cWHpgqx31zmi28NE=","subType":"0"}},"keyId":6875251194940358707}},"$audit":{"$impersonatedUsers":[{"user":"xxxx","db":"xxxx"}],"$impersonatedRoles":[{"role":"readWrite","db":"xxxx"}]},"$client":{"driver":{"name":"mongo-java-driver","version":"3.9.1"},"os":{"type":"Linux","name":"Linux","architecture":"amd64","version":"5.4.0-1021-aws"},"platform":"Java/Private Build/1.8.0_265-8u265-b01-0ubuntu2~20.04-b01","mongos":{"host":"xxxx:27017","client":"xxxxx","version":"4.4.1"}},"$configServerState":{"opTime":{"ts":{"$timestamp":{"t":1610156725,"i":79}},"t":12}},"$db":"xxxx"},"planSummary":"IXSCAN { entityId: \"hashed\" }","keysExamined":73,"docsExamined":73,"hasSortStage":true,"cursorExhausted":true,"numYields":8,"nreturned":73,"queryHash":"F305D754","planCacheKey":"42D383C3","reslen":397160,"locks":{"ReplicationStateTransition":{"acquireCount":{"w":9}},"Global":{"acquireCount":{"r":9}},"Database":{"acquireCount":{"r":9}},"Collection":{"acquireCount":{"r":9}},"Mutex":{"acquireCount":{"r":3}}},"readConcern":{},"storage":{"data":{"bytesRead":5215788,"timeReadingMicros":129685}},"protocol":"op_msg","durationMillis":132}}

Mongos log

{"t":{"$date":"2020-12-31T02:19:33.680+00:00"},"s":"I",  "c":"COMMAND",  "id":51803,   "ctx":"conn128","msg":"Slow query","attr":{"type":"command","ns":"xxxx.companyPriority","command":{"find":"companyPriority","filter":{"_id":{"$in":[{"$oid":"5319df10e4b0f7e16602a313"}]}},"$db":"xxxx","$clusterTime":{"clusterTime":{"$timestamp":{"t":1609381171,"i":2}},"signature":{"hash":{"$binary":{"base64":"C2cNRe4vAhiBs97T6VYXIYYU1Ck=","subType":"0"}},"keyId":6877905033757720578}},"lsid":{"id":{"$uuid":"ba72a15f-2568-43e9-8c9a-abd7bd2aa6be"}}},"nShards":1,"cursorExhausted":true,"numYields":0,"nreturned":1,"reslen":278,"protocol":"op_msg","durationMillis":2007}}

"queryHash":"F305D754" is present in mongod log and no queryHash key in mongos The documentation nowhere mentions about the queryHash availability (or the absence of it) on mongos server logs separately. Is this expected behaviour or some configuration changes are required to get queryHash in mongos logs?

Note: mongos and mongod both are running on version 4.4.1

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    Per the issue you raised in the MongoDB Jira issue tracker (jira.mongodb.org/browse/SERVER-53859), it looks like this may be a useful logging improvement. Those interested should watch & upvote the Jira issue.
    – Stennie
    Commented Feb 1, 2021 at 8:27

1 Answer 1

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This is expected behaviour by design i.e currently queryHash is not available for mongos logs. As mentioned in the comment to the question, this has been picked as a improvement for future release. Closing the question.

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