Re: Proposal: Conflict log history table for Logical Replication

On Mon, Oct 26, 2026 at 9:08 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Sat, Oct 24, 2026 at 11:42 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > The current use of the "datestyle" and other GUCs in libpqwalreceiver
> > or in other places is to keep the format portable across nodes but
> > here the CLT output will be usually human-readable. So, the same
> > analogy doesn't follow here. I am not convinced that this required
> > mid-way changing the GUCs temporarily. I feel we can document this
> > column and if we still get a request from field for portability of
> > this field(s) then we can consider using GUCs to make the format
> > consistent.
> >
>
> But it causes ambiguous results as shown in [1]. I am not sure how
> documentation will help here. As I see it, the stored key must
> convert back to the original value, not to some other value,
> especially since the patch’s own docs recommend casting it back to the
> column type before comparing. And I don’t think libpqwalreceiver does
> this for portability: its comment says it forces these GUCs so values
> are output “in a form that is unambiguous to the subscriber.” IMO,
> that’s the same goal here: avoiding a wrong stored value, not
> portability.
>

That is a cross-node compatibility case and similarly pg_dump's output
could be restored on another node. I feel if a user changes the
datestyle or similar settings in-between different conflict-insertions
the results can change accordingly. We shouldn't take such guarantees.
It should be documented somewhere along with the following text [1],
we can probably give a small example as well.

[1]
+ <para>
+ The apply worker's <xref linkend="guc-bytea-output"/> and
+ <xref linkend="guc-quote-all-identifiers"/> settings change how a value
+ is written without changing the value itself. If these settings differ
+ between conflicts, the same key can be recorded in different but
+ equivalent forms, and comparing the recorded text may miss some of them.

--
With Regards,
Amit Kapila.