Re: Proposal: Conflict log history table for Logical Replication - Mailing list pgsql-hackers

On Wed, Apr 29, 2026 at 12:34 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> On Wed, Apr 29, 2026 at 11:50 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > On Tue, Apr 28, 2026 at 7:53 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > > > 2.
> > > > +typedef enum ConflictLogDest
> > > > +{
> > > > + /* Log conflicts to the server logs */
> > > > + CONFLICT_LOG_DEST_LOG   = 1 << 0,   /* 0x01 */
> > > > +
> > > > + /* Log conflicts to an internally managed conflict log table */
> > > > + CONFLICT_LOG_DEST_TABLE = 1 << 1,   /* 0x02 */
> > > > +
> > > > + /* Convenience bitmask for all supported destinations */
> > > > + CONFLICT_LOG_DEST_ALL   = (CONFLICT_LOG_DEST_LOG | CONFLICT_LOG_DEST_TABLE)
> > > > +} ConflictLogDest;
> > > > +
> > > > +/*
> > > > + * Array mapping for converting internal enum to string.
> > > > + */
> > > > +static const char *const ConflictLogDestNames[] = {
> > > > + [CONFLICT_LOG_DEST_LOG] = "log",
> > > > + [CONFLICT_LOG_DEST_TABLE] = "table",
> > > > + [CONFLICT_LOG_DEST_ALL] = "all"
> > > > +};
> > > >
> > > > Defining an array this way could be an Array size issue. Actually the
> > > > array has just three elements so the last element should be at
> > > > ConflictLogDestNames[2] but if we go by the above definition, it will
> > > > be ConflictLogDestNames[3]. Can we define by referring the following
> > > > existing way:
> >
> > I was analyzing this because I remember we were initially using the
> > format you suggested and switched to the bit format to enable direct
> > bitwise operations elsewhere.  I think Peter suggested that [1], and
> > the argument was that the bitwise operation is easy if we represent
> > them as a bit. Also, since we would not have too many options, the
> > array size shouldn't be an issue.  But I understand your point: adding
> > more elements will cause the array size to grow very fast as this is
> > using sparse array.  Let's see what others think about this, and then
> > we can decide whether to change it back?
> >
>
> The benefit of the current approach is that checking whether the
> destination is TABLE becomes straightforward:
>
> IsSet(opts.conflictlogdest,CONFLICT_LOG_DEST_TABLE)
>
> if we go by regular enum values (simialr to XLogSource), then it will be:
>
>  if (opts.logdest == CONFLICT_LOG_DEST_TABLE ||
>      opts.logdest == CONFLICT_LOG_DEST_ALL)

Right

> For ease of extending the enum and its corresponding text mappings, my
> personal preference is still the regular (non-bitwise) enum approach.

Yeah, that's my personal preference too.  But Peter had strong stand
on keeping as bitwise so that we can directly use
IsSet(opts.conflictLogDest, CONFLICT_LOG_DEST_TABLE) operations.
Since this array shouldn't have many options, a sparse array is not an
issue.  So lets see what @Peter Smith has to say here and then we can
build a concensus on this.

> But if we anticipate adding more destination options in the future
> that would be covered by ALL, checking for those in code could lead to
> growing chains of OR conditions, whereas the bitwise approach scales
> more cleanly in that respect. So I think the choice depends on what
> kinds of future extensions we expect.
>
> Do we have plans to add more options that would naturally fall under
> ALL? Or do we instead expect additions that are mutually exclusive;
> for example, splitting CONFLICT_LOG_DEST_LOG into something like
> CONFLICT_LOG_DEST_JSON_LOG and CONFLICT_LOG_DEST_TEXT_LOG, which may
> not make sense to group under ALL in the same way?

Currently, I haven't considered which options would naturally fall
under "ALL." Perhaps if we plan targets other than logs and files,
those might also fall under "ALL."

--
Regards,
Dilip Kumar
Google