Re: [PATCH] Teach pg_waldump to extract FPIs from the WAL

On Sat, 23 Apr 2022 at 00:51, David Christensen
<david.christensen@crunchydata.com> wrote:
>
> Hi -hackers,
>
> Enclosed is a patch to allow extraction/saving of FPI from the WAL
> stream via pg_waldump.
>
> Description from the commit:
>
> Extracts full-page images from the WAL stream into a target directory,
> which must be empty or not
> exist.  These images are subject to the same filtering rules as normal
> display in pg_waldump, which
> means that you can isolate the full page writes to a target relation,
> among other things.
>
> Files are saved with the filename: <lsn>.<ts>.<db>.<rel>.<blk> with
> formatting to make things

Regardless of my (lack of) opinion on the inclusion of this patch in
PG (I did not significantly review this patch); I noticed that you do
not yet identify the 'fork' of the FPI in the file name.

A lack of fork identifier in the exported file names would make
debugging much more difficult due to the relatively difficult to
identify data contained in !main forks, so I think this oversight
should be fixed, be it through `_forkname` postfix like normal fork
segments, or be it through `.<forknum>` numerical in- or postfix in
the filename.

-Matthias