Hi,
I have a cluster with 3 members. The queries for the public API go to the secondaries and the queries for the developer dashboard / management UI go to the primary node to distribute the load.
There is no other setting like “Nearest” or so to configure the read preference.
I would expect that the two secondaries have similar queries characteristics regarding load and query targeting. But it is totally different:
You can see it here: MongoDB Free Monitoring
I thought that the index might be corrupt or so but my test queries produce the same results. I make a test query and run explain on both secondaries individually.
Is there anything I can do to check what is going on here?
EDIT: I just restarted mongo-1, you might see it in the charts.
EDIT 2: The primary has not changed the last 7 days.
I also see very weird entries in the profiler:
{
"op" : "query",
"ns" : "SquidexContentV3.States_Contents_Published3",
"command" : {
"find" : "States_Contents_Published3",
"filter" : {
"mt" : {
"$exists" : true
},
"id" : {
"$exists" : true
},
"_ai" : "16a2ca1c-6871-4a8d-9c21-98d47652355c",
"_si" : {
"$in" : [
"5a050a0a-ee27-45a5-958d-39a4adfc2802"
]
},
"dl" : {
"$ne" : true
},
"do.Slug.iv" : "BandeauListeAnnonce",
"do.Site.iv" : "Amivac"
},
"sort" : {
"mt" : -1,
"id" : 1
},
"limit" : 200,
"$db" : "SquidexContentV3",
"$readPreference" : {
"mode" : "secondary"
},
"lsid" : {
"id" : UUID("2284bc5a-ca9d-4093-b1f2-ff56e12cb13a")
},
"$clusterTime" : {
"clusterTime" : Timestamp(1656406366, 10),
"signature" : {
"hash" : BinData(0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : 0
}
}
},
"keysExamined" : 6,
"docsExamined" : 5,
"hasSortStage" : true,
"cursorExhausted" : true,
"numYield" : 0,
"nreturned" : 0,
"queryHash" : "A13373FD",
"planCacheKey" : "41B8B1E5",
"locks" : {
"ReplicationStateTransition" : {
"acquireCount" : {
"w" : 2
}
},
"Global" : {
"acquireCount" : {
"r" : 2
}
},
"Database" : {
"acquireCount" : {
"r" : 1
}
},
"Collection" : {
"acquireCount" : {
"r" : 1
}
},
"Mutex" : {
"acquireCount" : {
"r" : 1
}
}
},
"flowControl" : {
},
"storage" : {
},
"responseLength" : 257,
"protocol" : "op_msg",
"millis" : 556,
"planSummary" : "IXSCAN { _si: 1, dl: 1, mt: -1 }",
"execStats" : {
"stage" : "CACHED_PLAN",
"nReturned" : 0,
"executionTimeMillisEstimate" : 0,
"works" : 1,
"advanced" : 0,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"inputStage" : {
"stage" : "SORT",
"nReturned" : 0,
"executionTimeMillisEstimate" : 0,
"works" : 7,
"advanced" : 0,
"needTime" : 6,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"sortPattern" : {
"mt" : -1,
"id" : 1
},
"memLimit" : 104857600,
"limitAmount" : 200,
"type" : "simple",
"totalDataSizeSorted" : 0,
"usedDisk" : false,
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"$and" : [
{
"mt" : {
"$exists" : true
}
},
{
"_ai" : {
"$eq" : "16a2ca1c-6871-4a8d-9c21-98d47652355c"
}
},
{
"do.Site.iv" : {
"$eq" : "Amivac"
}
},
{
"do.Slug.iv" : {
"$eq" : "BandeauListeAnnonce"
}
},
{
"id" : {
"$exists" : true
}
}
]
},
"nReturned" : 0,
"executionTimeMillisEstimate" : 0,
"works" : 6,
"advanced" : 0,
"needTime" : 5,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"docsExamined" : 5,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 5,
"executionTimeMillisEstimate" : 0,
"works" : 6,
"advanced" : 5,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"keyPattern" : {
"_si" : 1,
"dl" : 1,
"mt" : -1
},
"indexName" : "_si_1_dl_1_mt_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"_si" : [
],
"dl" : [
],
"mt" : [
]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"_si" : [
"[\"5a050a0a-ee27-45a5-958d-39a4adfc2802\", \"5a050a0a-ee27-45a5-958d-39a4adfc2802\"]"
],
"dl" : [
"[MinKey, true)",
"(true, MaxKey]"
],
"mt" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 6,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0
}
}
}
},
"ts" : ISODate("2022-06-28T08:52:46.742+0000"),
"client" : "10.0.0.10",
"allUsers" : [
],
"user" : ""
}
no yields, no locks, zero results, index scan and still it takes a lot of time.