[SERVER-30898] Gate array sorting semantic changes behind featureCompatibilityVersion Created: 30/Aug/17  Updated: 06/Dec/22  Resolved: 05/Sep/17

Status: Closed
Project: Core Server
Component/s: Aggregation Framework, Querying
Affects Version/s: None
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Charlie Swanson Assignee: Backlog - Query Team (Inactive)
Resolution: Won't Fix Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Assigned Teams:
Query
Operating System: ALL
Participants:

 Description   

In a mixed version sharded cluster, multiple shards can participate in the merge, each using different sorting semantics. Consider an aggregation that targets two shards, one is version 3.6 and one is version 3.4, then is merged by the 3.6 node. The results from the 3.4 node will come back in a different order than they would on the 3.6 node, but the 3.6 merging node will assume they are both sorted the same way, incorrectly using a 'merge presorted streams' algorithm, for streams that aren't actually sorted.



 Comments   
Comment by David Storch [ 05/Sep/17 ]

Since array sorting semantics are not usefully or consistently defined in versions prior to 3.6, we do not believe it is important to preserve useful array sorting behavior in a mixed version 3.4/3.6 cluster. Users who fully upgrade to 3.6, however, should get a meaningful sort order when sorting on an array field. Closing as Won't Fix.

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