#40206 added parsing for the various row-level lock modes, and treats them like no-ops. This is acceptable for CockroachDB, which only supports SERIALIZABLE transactions, because from a client's perspective there's no way to observe whether any particular transaction needed to be restarted because of a conflict on the rows that were declared as FOR UPDATE, or because of some other conflict - the transaction will have to be restarted in either case.

This issue tracks improving this behavior for performance reasons. There's ongoing work in core to support at least some of these semantics.