Re: pg_waldump: support decoding of WAL inside tarfile

On Fri, Apr 3, 2026 at 1:11 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> In any case, this is all completely moot if we don't write code to
> de-sparse a sparse entry: we will not be able to validate WAL data
> if the WAL file is missing some pages. So I see little point in
> having code that tolerates pax headers if it doesn't also do that.

Yeah. FWIW I spent a few hours hacking on that the other day and
could decode many files, but I now realise that the task was made more
difficult by a problem you fixed: without header validation, small
mistakes resulted in corruption or went bananas. With that now
addressed, I hope I can get it into shape and propose it for the next
cycle...

For what it's worth, I was just speculating about how one might
reasonably handle unrecognised *non-standard* header names, not the
POSIX-standardised ones which, you're right, we'd probably need to
grok properly. If we assumed reasonable engineering decisions
following (what I understood to be) the spirit of pax, maybe we could
assume that new non-standard headers either don't affect file contents
and thus could be ignored (think: GNU.windows.permissions=...), or do
affect file contents but have measures in place to prevent unknown
encodings from being exposed to unsuspecting software (think:
deathstation.byte=9bit). That's a position we could choose to take,
anyway, in the absence of a crystal ball... Fortunately there aren't
really many implementations of POSIX left, so it's not like we're
dealing with the Fermi Paradox here...