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Type:
Bug
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Resolution: Done
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Priority:
Critical - P2
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Affects Version/s: 2.2.0, 2.2.1
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Component/s: Aggregation Framework
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None
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ALL
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(copied to CRM)
Note: this seems to only be a problem with the aggregate command. In 2.2.x all other commands seem to ignore $readPreference (support is implemented in 2.3.1 for SERVER-7423)
This effects at least the Java and Python drivers, which always send $readPreference to mongos for certain white listed commands.
aggregate without $readPreference, no issues:
mongos> db.runCommand({'aggregate': 'test', 'pipeline': [{'$project': {'_id': false, 'foo': true}}]})
{ "result" : [ { }, { "foo" : "bar" } ], "ok" : 1 }
aggregate with $readPreference, errors:
mongos> db.runCommand({'aggregate': 'test', 'pipeline': [{'$project': {'_id': false, 'foo': true}}], $readPreference: {'mode': 'primary'}})
{ "ok" : 0, "errmsg" : "unrecognized field \"$readPreference" }
count (as one counter-example) with $readPreference, no issues:
mongos> db.runCommand({'count': 'test', query: {}, $readPreference: {'mode': 'primary'}})
{ "shards" : { "shard0000" : 2 }, "n" : 2, "ok" : 1 }