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Type:
Bug
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Resolution: Done
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Priority:
Major - P3
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None
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Affects Version/s: 3.6.4
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Component/s: Sharding
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Labels:None
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ALL
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A MongoDB v3.6.4 database on Debian 9.4 with a large sharded collection with two shards and WiredTiger engine hangs when issuing a findOne() or find() command without any parameters. The collection has only the default index on the _id key.
If findOne() or find() is invoked on any of the shards then it works immediately. If it is invoked on a mongos then it hangs.
With db.currentOp() this can be seen after findOne() is invoked:
{
"host" : "db1:27017",
"desc" : "conn277",
"connectionId" : 277,
"client" : "10.240.137.10:57294",
"appName" : "MongoDB Shell",
"clientMetadata" : {
"application" : {
"name" : "MongoDB Shell"
},
"driver" : {
"name" : "MongoDB Internal Client",
"version" : "3.6.4"
},
"os" : {
"type" : "Linux",
"name" : "PRETTY_NAME=\"Debian GNU/Linux 9 (stretch)\"",
"architecture" : "x86_64",
"version" : "Kernel 4.9.0-6-amd64"
},
"mongos" : {
"host" : "m1:27017",
"client" : "10.240.0.0:38190",
"version" : "3.6.4"
}
},
"active" : true,
"currentOpTime" : "2018-04-28T08:13:26.371+0200",
"opid" : 2148656,
"secs_running" : NumberLong(4),
"microsecs_running" : NumberLong(4344989),
"op" : "query",
"ns" : "somedb.somecol",
"command" : {
"find" : "somecol",
"limit" : NumberLong(1),
"shardVersion" : [
Timestamp(188696, 1),
ObjectId("5ac6b2abbd8bbc9f42f34a39")
],
"$clusterTime" : {
"clusterTime" : Timestamp(1524896001, 1),
"signature" : {
"hash" : BinData(0,"RuV/v6Qm7H9AvPMVRNH0jkdIwRM="),
"keyId" : NumberLong("6540622458888650772")
}
},
"$client" : {
"application" : {
"name" : "MongoDB Shell"
},
"driver" : {
"name" : "MongoDB Internal Client",
"version" : "3.6.4"
},
"os" : {
"type" : "Linux",
"name" : "PRETTY_NAME=\"Debian GNU/Linux 9 (stretch)\"",
"architecture" : "x86_64",
"version" : "Kernel 4.9.0-6-amd64"
},
"mongos" : {
"host" : "m1:27017",
"client" : "10.240.0.0:38190",
"version" : "3.6.4"
}
},
"$configServerState" : {
"opTime" : {
"ts" : Timestamp(1524896001, 1),
"t" : NumberLong(3)
}
},
"$db" : "feedback"
},
"planSummary" : "COLLSCAN",
"numYields" : 803,
"locks" : {
"Global" : "r",
"Database" : "r",
"Collection" : "r"
},
"waitingForLock" : false,
"lockStats" : {
"Global" : {
"acquireCount" : {
"r" : NumberLong(1608)
}
},
"Database" : {
"acquireCount" : {
"r" : NumberLong(804)
}
},
"Collection" : {
"acquireCount" : {
"r" : NumberLong(804)
}
}
}
},