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Type:
Question
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Resolution: Duplicate
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: MapReduce
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None
During the reduce phase of a map-reduce job I'm running, it seems the entire mongod process becomes locked. I believe the following output shows the global write lock being held (from db.currentOp()):
{
"opid" : 128630,
"active" : true,
"secs_running" : 626,
"op" : "query",
"ns" : "mr_universal_split_2.mr_collection0",
"query" : {
"$msg" : "query not recording (too large)"
},
"client" : "10.11.60.172:48370",
"desc" : "conn929",
"threadId" : "0x7e73fee9c700",
"connectionId" : 929,
"locks" : {
"^" : "W"
},
"waitingForLock" : false,
"msg" : "m/r: reduce post processing M/R Reduce Post Processing Progress: 3222/5517 58%",
"progress" : {
"done" : 3222,
"total" : 5517
},
"numYields" : 9040,
"lockStats" : {
"timeLockedMicros" : {
"R" : NumberLong(0),
"W" : NumberLong(79265742),
"r" : NumberLong(56685244),
"w" : NumberLong(728735)
},
"timeAcquiringMicros" : {
"R" : NumberLong(0),
"W" : NumberLong(44727900),
"r" : NumberLong(449781385),
"w" : NumberLong(164798959)
}
}
}
Is there a way to prevent map-reduce from holding the global write lock during the reduce phase? I recently modified the MR job by passing nonAtomic: true to the output specification. This improves the situation, but it still causes other clients to hang for many seconds before returning results from queries on unrelated databases.
- duplicates
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SERVER-13552 remove unnecessary global lock during "replace" out action
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- Backlog
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