[SERVER-66480] Create a new command to join a generic chunk migration on a donor/recipient shard. Created: 16/May/22  Updated: 29/Oct/23  Resolved: 24/May/22

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: 6.0.0-rc8, 6.1.0-rc0

Type: Task Priority: Major - P3
Reporter: Paolo Polato Assignee: Paolo Polato
Resolution: Fixed Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Backports
Depends
is depended on by SERVER-65831 BalancerCommandsScheduler::stop() sho... Closed
Backwards Compatibility: Fully Compatible
Backport Requested:
v6.0
Sprint: Sharding EMEA 2022-05-30
Participants:
Linked BF Score: 171

 Description   

On startup time, the Balancer needs to wait for the completion of all the outstanding chunk migrations executed across the cluster before generating new requests.

In the past this was achieved by persisting in config.migrations a recovery doc for every moveChunk requested and repeating the command for every unanswered one upon a config server step down/crash.

The same approach cannot be adopted to recover moveRange commands (which semantics are slightly different) without causing undesired side effects when the cluster gets downgraded.

A more generic alternative could be built upon a new command that allows a client to wait until the contacted shard is no longer involved in any migration activity.



 Comments   
Comment by Githook User [ 29/May/22 ]

Author:

{'name': 'Paolo Polato', 'email': 'paolo.polato@mongodb.com', 'username': 'ppolato'}

Message: SERVER-66480 introduce joinMigration shard cmd to set a barrier on the Balancer initialisation

(cherry picked from commit 531dfe764bc0645f5e676feaf5687100c0a5e612)
Branch: v6.0
https://github.com/mongodb/mongo/commit/9ae0a24f4d2323424784a941c783c7cf39c3ec20

Comment by Paolo Polato [ 24/May/22 ]

Author:

{'name': 'Paolo Polato', 'email': 'paolo.polato@mongodb.com', 'username': 'ppolato'}

Message: SERVER-66480 introduce joinMigration shard cmd to set a barrier on the Balancer initialisation
Branch: master
https://github.com/mongodb/mongo/commit/531dfe764bc0645f5e676feaf5687100c0a5e612

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