Re: pg_walinspect - a new extension to get raw WAL data and WAL stats

On Tue, Mar 22, 2022 at 11:30 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> > > To me duplicating this much code from waldump seems like a bad idea from a
> > > maintainability POV.
> >
> > Even if we were to put the above code from pg_walinspect and
> > pg_waldump into, say, walutils.c or some other existing file, there we
> > had to make if (pg_walinspect) appendStringInfo else if (pg_waldump)
> > printf() sort of thing, isn't it clumsy?
>
> Why is that needed? Just use the stringinfo in both places? You're outputting
> the exact same thing in both places right now. There's already a stringinfo in
> XLogDumpDisplayRecord() these days (there wasn't back when pg_xlogddump was
> written), so you could just convert at least the relevant printfs in
> XLogDumpDisplayRecord().
>
> > Also, unnecessary if
> > conditions need to be executed for every record. For maintainability,
> > I added a note in pg_walinspect.c and pg_waldump.c to consider fixing
> > things in both places (of course this might sound dumbest way of doing
> > it, IMHO, it's sensible, given the if(pg_walinspect)-else
> > if(pg_waldump) sorts of code that we need to do in the common
> > functions). Thoughts?
>
> IMO we shouldn't merge this with as much duplication as there is right now,
> the notes don't change that it's a PITA to maintain.

Here's a refactoring patch that basically moves the pg_waldump's
functions and stats structures to xlogreader.h/.c so that the
pg_walinspect can reuse them. If it looks okay, I will send the
pg_walinspect patches based on it.

Regards,
Bharath Rupireddy.