Summary
We are observing system-initiated queries on our MongoDB secondary server that exceed the maximum time limit (MaxTimeMSExpired). These queries are performed by the __system@local user.
Environment
- MongoDB Version: 5.0.18
Problem Description
We have identified queries in the system.profile collection that are initiated by the __system@local user. These queries are targeting the mp.test1 collection and are exceeding the specified maxTimeMS limit. Below is an example of one such document from the system.profile collection:
{
"op" : "query",
"ns" : "mp.test1",
"command" : {
"find" : "test1",
"filter" : {
"detailsId" : "668dcf000000000000000000"
},
"batchSize" : 1.0,
"singleBatch" : true,
"maxTimeMS" : 1000.0,
"$readPreference" : {
"mode" : "secondaryPreferred"
},
"readConcern" : {
"level" : "local"
},
"$db" : "mp"
},
"numYield" : 402.0,
"queryHash" : "75B43167",
"planCacheKey" : "9D7CG57B",
"locks" : {
"FeatureCompatibilityVersion" : {
"acquireCount" : {
"r" : NumberLong(404)
}
},
"Global" : {
"acquireCount" : {
"r" : NumberLong(403)
}
},
"Mutex" : {
"acquireCount" : {
"r" : NumberLong(1)
}
}
},
"flowControl" : {
},
"readConcern" : {
"level" : "local",
"provenance" : "clientSupplied"
},
"ok" : 0.0,
"errMsg" : "Executor error during find command :: caused by :: operation exceeded time limit",
"errName" : "MaxTimeMSExpired",
"errCode" : 50.0,
"responseLength" : 0.0,
"protocol" : "op_msg",
"millis" : 1002.0,
"planSummary" : "COLLSCAN",
"ts" : ISODate("2024-07-09T03:45:55.304+0000"),
"client" : "0.0.0.0",
"allUsers" : [
{
"user" : "__system",
"db" : "local"
}
],
"user" : "__system@local"
}
Why would MongoDB initiate such queries on a secondary server?