[SERVER-9287] Decision to split chunk should happen on shard mongod, not on mongos Created: 08/Apr/13  Updated: 29/Oct/19  Resolved: 07/Jun/19

Status: Closed
Project: Core Server
Component/s: Sharding
Affects Version/s: None
Fix Version/s: 4.2.0

Type: Improvement Priority: Major - P3
Reporter: Spencer Brody (Inactive) Assignee: Alyson Cabral (Inactive)
Resolution: Done Votes: 9
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Backports
Depends
is depended on by SERVER-16715 Distribution of data with hashed shar... Closed
is depended on by SERVER-11487 Don't make splits/merge bump up colle... Closed
Duplicate
is duplicated by SERVER-25060 Make SplitHeuristics.maxParallelSplit... Closed
is duplicated by SERVER-1327 Move splits and migrates out of conne... Closed
Related
related to SERVER-44088 Autosplitter seems to ignore some fat... Closed
related to SERVER-16963 mongos help doesn't list noAutoSplit ... Closed
related to SERVER-24604 Add doAutoSplit to config.settings Closed
related to SERVER-14121 Store size for chunk in config.chunks. Closed
related to SERVER-20448 allow sharding.autoSplit to be set at... Closed
is related to SERVER-9320 Several connections request to split ... Closed
is related to SERVER-10866 Figure out split triggering mechanism Closed
Backwards Compatibility: Fully Compatible
Backport Requested:
v4.2
Sprint: Sharding 2018-08-13
Participants:
Case:

 Description   

As it is, it's possible to get oversized chunks if data is being written to the same chunk from different mongoses, as each mongos would only see a small amount of data going to that chunk and thus won't trigger a chunk split. If the decision on when to split a chunk happened on the shard, then it could know exactly when 64Mb (or whatever the chunk size has been set to) has been written to a chunk, and thus can trigger a split at the right time and prevent chunks from ever going over the chunk size.



 Comments   
Comment by Alyson Cabral (Inactive) [ 07/Jun/19 ]

I'm happy to announce that starting in MongoDB 4.2, the decision to split a chunk has moved from the mongos to the mongod. Check out the release announcement for MongoDB 4.2 and get started with the release candidate through our downloads center. The release candidate will be available in Atlas shortly.

Please see the attached server tickets for further technical details.

 

Congratulations to matthew.saltz for his work on this project. 

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