Re: Automated way to find actual COMMIT LSN of subxact LSN

>
> It would seem like what you're asking for is to continue until the commit
> of the parent transaction, not just the next commit after the subcommit.
> Otherwise (if that's an unrelated xact) the subxact would still not be
> committed, so that you might as well have stopped short of it.
>

Right, the parent transaction is what I meant.

> I'd be in favor of that for recovery_target_xid, but I'm not at all
> convinced about changing the behavior for a target LSN. The fact that
> the target is a subcommit seems irrelevant when you specify by LSN.
>

Perhaps some context will help. There have been 2 cases in which I have
tried to do this, both of them based on logical decoding, and finding
either a transaction id or an LSN to recover to. Actually, the only reason
I have ever used transaction id instead of LSN is on <= 9.6 because the
latter isn't supported until pg10.

For this use case, my goal is simply to be able to recover the the point
immediately after a particular decoded log line is visible, without
necessarily having to find out the final parent transaction id.

Given this, I am open to different implementations but I would like to
either be able to specify an LSN or transaction ID, and have a feature that
allows the recovery target to roll forward just until it is visible, even
if the LSN or transaction ID is not the actual commit of the parent
transaction.

> I don't recall this for sure, but doesn't a parent xact's commit record
> include all subxact XIDs? If so, the implementation would just require
> searching the subxacts as well as the main XID for a match to
> recovery_target_xid.
>

Yes, I believe so.

Thanks,
Jeremy