Re: pg_waldump: support decoding of WAL inside tarfile

On 2026-04-01 We 8:16 PM, Thomas Munro wrote:
> On Thu, Apr 2, 2026 at 7:25 AM Tom Lane<tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Also, if we are admitting the possibility that what we are reading
>> was made by a platform-supplied tar and not our own code, I think
>> it verges on lunacy to behave as though unsupported typeflags are
>> regular files.
> Yeah, if this is the first time we parse files we didn't make then
> that makes total sense. I was a bit unsure of that question when I
> suggested we reject pax only after we've failed to find a file, in
> case there are scenarios that work today with harmless ignorable pax
> headers that don't change the file name.
>
>> So I think we need something more or less like the attached.
> LGTM. Tested with both tars here. I updated that little test patch
> for this. Not sure if you think it's worth a test though, now that
> it's so simple.
>
> @Andrew: I tried usingFile::Spec->devnull() this time. Are you able
> to check if this works OK on Windows, applied on top of Tom's patch?
> AFAIK should be able to run this new test and pass, not skip it. But
> it could be that the shell invocation needs tweaking. It's hard to
> tell from CI. (Huh, apparently Windows ships a copy of BSD tar as
> C:\Windows\System32\tar.exe these days.)

Yes, that appears to work. I would put a "2>&1" at the end - we don't
care about the output, just whether or not it succeeds:

C:\Windows\system32>perl -MFile::Spec -e "print File::Spec->devnull();"
nul

C:\Windows\system32>tar --no-read-sparse -c - nul > nul 2>&1 && echo hello

C:\Windows\system32>tar --no-read-sparse -c - nul > nul 2>&1 || echo hello
hello

cheers

andrew

--
Andrew Dunstan
EDB:https://www.enterprisedb.com