Re: pg_waldump: support decoding of WAL inside tarfile

On Mon, Aug 25, 2025 at 5:58 PM Amul Sul <sulamul(at)gmail(dot)com> wrote:
>
> On Thu, Aug 7, 2025 at 7:47 PM Amul Sul <sulamul(at)gmail(dot)com> wrote:
> > [....]
> > -----------------------------------
> > Known Issues & Status:
> > -----------------------------------
> > - Timeline Switching: The current implementation in patch 006 does not
> > correctly handle timeline switching. This is a known issue, especially
> > when a timeline change occurs on a WAL file that has been written to a
> > temporary location.
> >
>
> This is still pending and will be addressed in the next version.
> Therefore, patch 0006 remains marked as WIP.
>

After testing pg_waldump, I have realised that my previous
understanding of its timeline handling was incorrect. I had mistakenly
assumed by reading xlogreader code that it would use the same
timeline-switching logic found in xlogreader, without first verifying
this behavior. In testing, I found that pg_waldump does not follow
timeline switches. Instead, it expects all WAL files to be from a
single timeline, which is either specified by the user or determined
from the starting segment or default 1.

This is a positive finding, as it means we don't need to make
significant changes to align pg_waldump's current behavior. The
attached patches are now complete and no longer works in progress --
read for review. Additionally, I've dropped patch v2-0004 because it is
no longer necessary. The primary patches that implement the proposed
feature are now 0004 and 0005 in the attached set.

Regards,
Amul