[DOCS-11690] Docs for SERVER-34880: Make readConcern:local wait for write concern on a read-only transaction Created: 11/May/18  Updated: 27/Oct/23  Resolved: 18/Jun/18

Status: Closed
Project: Documentation
Component/s: None
Affects Version/s: None
Fix Version/s: 4.0.0-rc0

Type: Task Priority: Major - P3
Reporter: Kay Kim (Inactive) Assignee: Kay Kim (Inactive)
Resolution: Gone away Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Documented
documents SERVER-34880 Make readConcern:local wait for write... Closed
Related
is related to DOCS-11505 Document Transactions Closed
Participants:
Days since reply: 5 years, 34 weeks, 2 days ago
Epic Link: DOCS: 4.0 Server

 Description   

Description:

This change makes it so in 4.0, local readConcern for transactions works in the exact same way as majority and snapshot read concerns; if we had language stating otherwise it's no longer correct.

Scope of changes:

  • txn
  • readconcern-local

Impact to other docs outside of this product:

MVP:

Resources:

Engineering Ticket Description:

A transaction started with readConcern:local that doesn't do any writes does not need to wait for the data it read to be committed when the transaction commits.  SERVER-34038 implemented the behavior that causes read-only txns with RC 'majority' and 'snapshot' to wait for the data read to be committed at commit time, and intentionally excluded RC 'local' from that waiting.  However, since SERVER-34837 isn't going to get done for 4.0, we should temporarily make RC 'local' behave like RC 'majority' and 'snapshot' in this case, so that the fact that the readConcern default is incorrect will not be observable.



 Comments   
Comment by Tess Avitabile (Inactive) [ 18/Jun/18 ]

No, I do not think we should document this behavior. This change was made because we would like the default readConcern for an operation that can write to be majority, but in 4.0, the default readConcern for a transaction is local. We addressed this by making readConcern local behave identically to majority for transactions. However, if/when we make the default readConcern for a transaction be majority, then if a user explicitly specifies readConcern local, we would be free to skip the wait upon commit of a read-only transaction.

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