Re: pg_waldump: support decoding of WAL inside tarfile

On Fri, Mar 20, 2026 at 5:01 PM Amul Sul <sulamul(at)gmail(dot)com> wrote:
>
> On Fri, Mar 20, 2026 at 2:18 AM Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com> wrote:
> >
> > Hello!
> >
> > Path is ignored with a positional argument, I think this is a bug?
> >
> > This fails:
> >
> > pg_waldump --path /wal/dir 000000010000000000000001
> >
> > And this works:
> >
> > pg_waldump --path /wal/dir --start 0/01000028 --end 0/010020F8
> >
>
> Good catch! I've fixed this in the attached version and updated a test
> case to cover this scenario.
>
> > +{
> > + int fname_len = strlen(fname);
> > +
> >
> > Shouldn't this use size_t?
> >
>
> Okay, that can be used. I’ve done the same in the attached version.
>
> > + /*
> > + * Setup temporary directory to store WAL segments and set up an exit
> > + * callback to remove it upon completion.
> > + */
> > + setup_tmpwal_dir(waldir);
> >
> > Maybe this could be deferred to be created only on first use? If I
> > understand correctly, in a typical scenario waldump won't use this
> > temporary directory, yet it always creates it.
>
> Yeah, that optimization can be done, but passing the waldir -- which
> is only used once -- to the point where the first temp file is created
> would require quite a bit of code refactoring that doesn't seem to
> offer much gain, IMO.
>

Since Andrew also leans toward creating the directory only when
needed, I have reconsidered the approach. I think we can pass waldir
(the archive directory) via XLogDumpPrivate, and I’ve implemented that
in the attached version.

Regards,
Amul