Re: Something is wrong with wal_compression

Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> On Fri, Jan 27, 2023 at 11:14 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> If any tuples made by that transaction had reached disk,
>> we'd have a problem.

> The problem is that the WAL wasn't flushed, allowing the same xid to
> be allocated again after crash recovery. But for any data pages to
> hit the disk, we'd have to flush WAL first, so then it couldn't
> happen, no?

Ah, now I get the point: the "committed xact" seen after restart
isn't the same one as we saw before the crash, but a new one that
was given the same XID because nothing about the old one had made
it to disk yet.

> FWIW I also re-complained about the dangers of anyone
> relying on pg_xact_status() for its stated purpose after seeing
> tanager's failure[1].

Indeed, it seems like this behavior makes pg_xact_status() basically
useless as things stand.

regards, tom lane