i upgrade from 4.4.4 to 4.4.8 cluster.
cluster has three mongos,three data nodes and one config using replicate with three nodes.
i recently i find many slow logs on mongos,op_msg more than 1000ms。but data node there is no any more than 100ms.

i check io,mem,cpu, there is no stress on it. i guess exists problem on mongos.
but i can't find it.

mongos slow log:
{"t":

{"$date":"2021-10-11T21:15:25.154+08:00"}

,"s":"I", "c":"COMMAND", "id":51803, "ctx":"conn3042892","msg":"Slow query","attr":{"type":"command","ns":"wzjMonitor.expWzjMonitor","appName":"wzj_op","command":{"find":"expWzjMonitor","filter":

{"no":"YT3224052005840"}

,"projection":

{"no":1,"del":1,"curT":1,"oType":1,"matOrg":1,"_id":0}

,"$db":"wzjMonitor","$clusterTime":{"clusterTime":{"$timestamp":{"t":1633958124,"i":152}},"signature":{"hash":{"$binary":{"base64":"XbmmyAeBvyjB0IIpxpqKars52yg=","subType":"0"}},"keyId":6958985885933109266}},"lsid":{"id":

{"$uuid":"5b593b65-b82d-40e8-8c94-682d9e4abc3d"}

}},"nShards":1,"cursorExhausted":true,"numYields":0,"nreturned":1,"reslen":323,"protocol":"op_msg","durationMillis":1080}}

but i execute it just 2ms.
mongos> db.expWzjMonitor.find(

{"no":"YT3224052005840"}

).projection(

{"no":1,"del":1,"curT":1,"oType":1,"matOrg":1,"_id":0}

).explain("executionStats")
{
"queryPlanner" : {
"mongosPlannerVersion" : 1,
"winningPlan" : {
"stage" : "SINGLE_SHARD",
"shards" : [
{
"shardName" : "shard2",
"connectionString" : "shard2/srvdb303.yto.cloud:21002,srvdb305.yto.cloud:21002,srvdb307.yto.cloud:21002",
"serverInfo" :

{ "host" : "srvdb305.yto.cloud", "port" : 21002, "version" : "4.4.8", "gitVersion" : "83b8bb8b6b325d8d8d3dfd2ad9f744bdad7d6ca0" }

,
"plannerVersion" : 1,
"namespace" : "wzjMonitor.expWzjMonitor",
"indexFilterSet" : false,
"parsedQuery" : {
"no" :

{ "$eq" : "YT3224052005840" }

},
"winningPlan" : {
"stage" : "PROJECTION_SIMPLE",
"transformBy" :

{ "no" : 1, "del" : 1, "curT" : 1, "oType" : 1, "matOrg" : 1, "_id" : 0 }

,
"inputStage" : {
"stage" : "SHARDING_FILTER",
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"no" :

{ "$eq" : "YT3224052005840" }

},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" :

{ "no" : "hashed" }

,
"indexName" : "no_hashed",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" :

{ "no" : [ "[-857763331883698335, -857763331883698335]" ] }

}
}
}
},
"rejectedPlans" : [ ]
}
]
}
},
"executionStats" : {
"nReturned" : 1,
"executionTimeMillis" : 2,
"totalKeysExamined" : 1,
"totalDocsExamined" : 1,
"executionStages" : {
"stage" : "SINGLE_SHARD",
"nReturned" : 1,
"executionTimeMillis" : 2,
"totalKeysExamined" : 1,
"totalDocsExamined" : 1,
"totalChildMillis" : NumberLong(0),
"shards" : [
{
"shardName" : "shard2",
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 0,
"totalKeysExamined" : 1,
"totalDocsExamined" : 1,
"executionStages" : {
"stage" : "PROJECTION_SIMPLE",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"transformBy" :

{ "no" : 1, "del" : 1, "curT" : 1, "oType" : 1, "matOrg" : 1, "_id" : 0 }

,
"inputStage" : {
"stage" : "SHARDING_FILTER",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"chunkSkips" : 0,
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"no" :

{ "$eq" : "YT3224052005840" }

},
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"docsExamined" : 1,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"keyPattern" :

{ "no" : "hashed" }

,
"indexName" : "no_hashed",
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" :

{ "no" : [ "[-857763331883698335, -857763331883698335]" ] }

,
"keysExamined" : 1,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
}
}
}
]
}
},
"serverInfo" :

{ "host" : "srvdb303.yto.cloud", "port" : 21051, "version" : "4.4.8", "gitVersion" : "83b8bb8b6b325d8d8d3dfd2ad9f744bdad7d6ca0" }

,
"ok" : 1,
"operationTime" : Timestamp(1633958637, 1646),
"$clusterTime" : {
"clusterTime" : Timestamp(1633958637, 1649),
"signature" :

{ "hash" : BinData(0,"yhztP+fehpQiXUYJNGyv/zitOrc="), "keyId" : NumberLong("6958985885933109266") }

}
}