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Type:
Bug
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Resolution: Won't Fix
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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
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Storage Execution
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OS X
This ticket branches off from SERVER-13442.
We noticed performance impact with multiple concurrent map/reduce jobs running, outputting into the same collection. The more jobs, the slower they got.
On SERVER-13442, rui.zhang determined that it was mostly a problem on Mac OS X.
A single map/reduce job in my test takes 9 seconds:
Thu Apr 3 11:22:40.114 [conn25] command test.$cmd command: { mapReduce: "docs", map: function () {
emit(this.office, this.age);
..., reduce: function (office, ages) {
return Array.sum(a..., out: { replace: "result", db: "test" } } ntoreturn:1 keyUpdates:0 numYields: 10008 locks(micros) W:2742 r:16146697 w:987 reslen:160 9068ms
But when running 4 identical map/reduce jobs concurrently, with the same output collection, each of them takes 90 seconds:
Thu Apr 3 11:21:52.854 [conn22] command test.$cmd command: { mapReduce: "docs", map: function () {
emit(this.office, this.age);
..., reduce: function (office, ages) {
return Array.sum(a..., out: { replace: "result", db: "test" } } ntoreturn:1 keyUpdates:0 numYields: 10068 locks(micros) W:958 r:158963049 w:2542 reslen:160 91595ms
My test was on a MacBook Pro, with SSD, 16GB RAM. 1 million documents of this schema with 4 different offices.
{
"_id" : ObjectId("533c4da2fe4dce47b0a093e8"),
"age" : 24,
"name" : "LqiU3l0hAM",
"office" : "dublin"
}
Map/Reduce functions:
var mapFunction = function() { emit(this.office, this.age); }; var reduceFunction = function(office, ages) { return Array.sum(ages); }; db.runCommand({mapReduce: 'docs', map: mapFunction, reduce: reduceFunction, out: {reduce: "result", db: "test"}}) printjson(db.result.find().toArray());
Then I just started several of these on the shell, with
mongo mr.js & mongo mr.js & mongo mr.js ...
- is related to
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SERVER-13442 mapReduce nonAtomic output option
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- Closed
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