Details
Major - P3 Description
If you trying to query some additional info from another collection(for example "foo") for "map" callback,
it works only if there is copy of "foo" at every shard, that will run this MR job.
Is it right or not?
Even if you create "Mongo" instance like this "new Mongo('host:port');" ?
Code for reproduce this:
// foo
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db.foo.insert({foo: 1});
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db.foo.insert({foo: 2});
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// sharding
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sh.enableSharding('current_db');
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sh.shardCollection('current_db.barSharded', {_id: 1});
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// insert 10m rows
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for (var i = 0; i < 10000000; ++i) {
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db.barSharded.insert({i: i});
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}
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var map = function() {
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var db = (new Mongo()).getDB(database);
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if (!db.foo.findOne()) {
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throw "reproduced";
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}
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}
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var reduce = function(rows) {}
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db.barSharded.mapreduce(map, reduce, {out: "baz"});
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