Re: pg_waldump: support decoding of WAL inside tarfile

On Fri, Apr 3, 2026 at 12:43 PM Sami Imseih <samimseih(at)gmail(dot)com> wrote:
> The --format=ustar has a limit of 2^21 (2097151) for UID/GID [1]
> and on my machine the UID is 10012663.
>
> So I found that one way to deal with this is to run the tar command with
> --owner=0 --group=0. As far as I can tell, the owner and group IDs don't
> matter for these tests, so maybe that is OK.
>
> @@ -1333,6 +1333,10 @@ sub tar_portability_options
> == 0)
> {
> push(@tar_p_flags, "--format=ustar");
> + # ustar format supports UIDs only up to 2^21 (2097151).
> + # Override owner/group to avoid failures on systems where
> + # the running user's UID/GID exceeds that limit.
> + push(@tar_p_flags, "--owner=0", "--group=0");

Interesting. BSD tar accepts those too, so here's an update to my
previous patch.

> While this fixes the test, I am now not sure what the broader implications are
> for --format=ustar for pg_waldump in the broader discussion?

I think users who have their own tar scripts will mostly be
unaffected, but a small minority will see the new error if they try to
use pg_verifybackup or pg_waldump, and they'll find their way to
--format=ustar, and then they might see the UID/GID error in their own
.tar production scripts, and find their way to adding those switches
too. Seems OK? Especially with a documentation note once we've
settle all of this.