On 2022-07-11 16:11:53 -0400, Robert Haas wrote:
> On Mon, Jul 11, 2022 at 3:34 PM Andres Freund <andres@anarazel.de> wrote:
> > Seems pretty simple to do. Have write_relmapper_file() write to a .tmp file
> > first (likely adding O_TRUNC to flags), use durable_rename() to rename it into
> > place. The tempfile should probably be written out before the XLogInsert(),
> > the durable_rename() after, although I think it'd also be correct to more
> > closely approximate the current sequence.
>
> Something like this?
Yea. I've not looked carefully, but on a quick skim it looks good.
> I chose not to use durable_rename() here, because that allowed me to
> do more of the work before starting the critical section, and it's
> probably slightly more efficient this way, too. That could be changed,
> though, if you really want to stick with durable_rename().
I guess I'm not enthused in duplicating the necessary knowledge in evermore
places. We've forgotten one of the magic incantations in the past, and needing
to find all the places that need to be patched is a bit bothersome.
Perhaps we could add extract helpers out of durable_rename()?
OTOH, I don't really see what we gain by keeping things out of the critical
section? It does seem good to have the temp-file creation/truncation and write
separately, but after that I don't think it's worth much to avoid a
PANIC. What legitimate issue does it avoid?
Greetings,
Andres Freund
