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.