Re: Diagnostic comment in LogicalIncreaseXminForSlot

On Mon, Jul 5, 2021 at 12:54 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Fri, May 21, 2021 at 6:00 PM Ashutosh Bapat
> <ashutosh.bapat@enterprisedb.com> wrote:
> >
> > It's there in CF. I am fine with PG-15. It will be good to patch the back-branches to have this extra diagnostic information available.
>
> The patch looks to me.
>

{
  slot->candidate_catalog_xmin = xmin;
  slot->candidate_xmin_lsn = current_lsn;
+ elog(DEBUG1, "got new catalog_xmin %u at %X/%X", xmin,
+ LSN_FORMAT_ARGS(current_lsn));
  }
  SpinLockRelease(&slot->mutex);

Today, again looking at this patch, I don't think doing elog inside
spinlock is a good idea. We can either release spinlock before it or
use some variable to remember that we need to write such an elog and
do it after releasing the lock. What do you think?

I have noticed that
a nearby function LogicalIncreaseRestartDecodingForSlot() logs similar
information after releasing spinlock, so it is better to follow the
same here as well.