[SERVER-25441] $lookup does not respect readConcern when aggregation on sharded collection Created: 04/Aug/16  Updated: 19/Nov/16  Resolved: 03/Nov/16

Status: Closed
Project: Core Server
Component/s: Aggregation Framework
Affects Version/s: 3.2.8, 3.3.10
Fix Version/s: 3.4.0-rc3

Type: Bug Priority: Major - P3
Reporter: Charlie Swanson Assignee: James Wahlin
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Backwards Compatibility: Fully Compatible
Operating System: ALL
Sprint: Query 2016-11-21
Participants:

 Description   

When an aggregation is run against a sharded collection with a $lookup stage, the merging shard that will perform the $lookup does not get propagated information about which readConcern was requested.



 Comments   
Comment by Githook User [ 03/Nov/16 ]

Author:

{u'username': u'jameswahlin', u'name': u'James Wahlin', u'email': u'james.wahlin@10gen.com'}

Message: SERVER-25441 $lookup on a sharded coll does not respect readConcern
Branch: master
https://github.com/mongodb/mongo/commit/481ad0d0a876f43da0ccfd5ba4e9c81a583c1dac

Comment by James Wahlin [ 31/Oct/16 ]

On review, $lookup does respect readConcern and is validated by readCommitted_lookup.js. Tests are performed against both a replica set and a cluster with unsharded collections.

The concern that readConcern is not passed to the merging shard (when running against a sharded collection) is valid. I modified the cluster test in readCommitted_lookup.js to run against a sharded local collection. This fails and the $mergeCursors command is run without the specified readConcern.

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