Re: Conflict detection for update_deleted in logical replication

On Tue, Jul 1, 2025 at 10:31 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Mon, Jun 30, 2025 at 6:59 PM Zhijie Hou (Fujitsu)
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > On Mon, Jun 30, 2025 at 7:22 PM Amit Kapila wrote:
> > >
>
> I was looking at 0001, it mostly looks fine to me except this one
> case. So here we need to ensure that commits must be acquired after
> marking the flag, don't you think we need to ensure strict statement
> ordering using memory barrier, or we think it's not required and if so
> why?
>
> RecordTransactionCommitPrepared()
> {
> ..
> + MyProc->delayChkptFlags |= DELAY_CHKPT_IN_COMMIT;
> +
> + /*
> + * Note it is important to set committs value after marking ourselves as
> + * in the commit critical section (DELAY_CHKPT_IN_COMMIT). This is because
> + * we want to ensure all transactions that have acquired commit timestamp
> + * are finished before we allow the logical replication client to advance
> + * its xid which is used to hold back dead rows for conflict detection.
> + * See maybe_advance_nonremovable_xid.
> + */
> + committs = GetCurrentTimestamp();
> }

I'm unsure whether the function call inherently acts as a memory
barrier, preventing the compiler from reordering these operations.
This needs to be confirmed.

--
Regards,
Dilip Kumar
Google