Re: Show various offset arrays for heap WAL records

On Mon, Jan 9, 2023 at 1:58 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> A couple times when investigating data corruption issues, the last time just
> yesterday in [1], I needed to see the offsets affected by PRUNE and VACUUM
> records. As that's probably not just me, I think we should make that change
> in-tree.

I remember how useful this was when we were investigating that early
bug in 14, that turned out to be in parallel VACUUM. So I'm all in
favor of it.

> The attached patch adds details to XLOG_HEAP2_PRUNE, XLOG_HEAP2_VACUUM,
> XLOG_HEAP2_FREEZE_PAGE.

I'm bound to end up doing the same in index access methods. Might make
sense for the utility routines to live somewhere more centralized, at
least when code reuse is likely. Practically every index AM has WAL
records that include a sorted page offset number array, just like
these ones. It's a very standard thing, obviously.

> I chose to include infomask[2] for the different freeze plans mainly because
> it looks odd to see different plans without a visible reason. But I'm not sure
> that's the right choice.

I don't think that it is particularly necessary to do so in order for
the output to make sense -- pg_waldump is inherently a tool for
experts. What it comes down to for me is whether or not this
information is sufficiently useful to display, and/or can be (or needs
to be) controlled via some kind of verbosity knob.

I think that it easily could be useful, and I also think that it
easily could be a bit annoying. How hard would it be to invent a
general mechanism to control the verbosity of what we'll show for each
WAL record?

--
Peter Geoghegan