[SERVER-4540] Allow specification of a shard key for sharded map/reduce output Created: 21/Dec/11  Updated: 06/Dec/22  Resolved: 09/Mar/20

Status: Closed
Project: Core Server
Component/s: Sharding
Affects Version/s: 2.0.0
Fix Version/s: None

Type: Improvement Priority: Major - P3
Reporter: Colin Marc Assignee: [DO NOT USE] Backlog - Sharding Team
Resolution: Won't Fix Votes: 1
Labels: map_reduce, sharding
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
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Assigned Teams:
Sharding
Participants:

 Description   

According to the map/reduce "sharded output" documentation, the sharded collection created by a map/reduce with sharded flag uses _id as the shard key. It would be really helpful to be able to specify a shard key for the output collection.



 Comments   
Comment by Charlie Swanson [ 09/Mar/20 ]

This is not an improvement we plan on making. However, the aggregation framework and the $merge stage can merge to a collection with a different shard key.

Comment by Santiago Alessandri [ 10/Jun/14 ]

+1

This is a feature that would be extremely helpful. Not always - and I might say most of the time - the best sharding key is not the _ id field.

I haven't found a decent workaround for this issue.

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