[SERVER-76309] Re-enable support for high water mark tokens in serverless Created: 19/Apr/23  Updated: 24/Apr/23

Status: Open
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Task Priority: Major - P3
Reporter: Mickey Winters Assignee: Backlog - Query Execution
Resolution: Unresolved Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Related
related to SERVER-76288 While a split or merge is being commi... Closed
Assigned Teams:
Query Execution
Participants:

 Description   

during PM-2341 in SERVER-76288 we disabled generation the mechanism for high water mark tokens in serverless since we could wind up returning hwmt with a time stamp greater than the block timestamp which could result in skipping events if a split or merge happens. this feature need to be reenabled somehow for change streams to work properly with sharding in serverless



 Comments   
Comment by Mickey Winters [ 24/Apr/23 ]

the previous mechanism would send a new hwmt when another tenant does a write which is an issue for shard split. so this needs to be redone to look at the last timestamp in that tenant's change collection instead of the last event in the oplog. the last timestamp in the oplog is problematic because if there is a split a non migrating tenant can do writes during the critical section and a migrating tenant might wind up with a resume token with a time stamp after the split operation's blockTS

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