Re: promotion related handling in pg_sync_replication_slots()

On Fri, Apr 12, 2024 at 7:47 AM shveta malik <shveta.malik@gmail.com> wrote:
>
> On Sat, Apr 6, 2024 at 11:49 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> >
> > Few comments:
> > ==============
> > 1.
> >  void
> >  SyncReplicationSlots(WalReceiverConn *wrconn)
> >  {
> > + /*
> > + * Startup process signaled the slot sync to stop, so if meanwhile user
> > + * has invoked slot sync SQL function, simply return.
> > + */
> > + SpinLockAcquire(&SlotSyncCtx->mutex);
> > + if (SlotSyncCtx->stopSignaled)
> > + {
> > + ereport(LOG,
> > + errmsg("skipping slot synchronization as slot sync shutdown is
> > signaled during promotion"));
> > +
> > + SpinLockRelease(&SlotSyncCtx->mutex);
> > + return;
> > + }
> > + SpinLockRelease(&SlotSyncCtx->mutex);
> >
> > There is a race condition with this code. Say during promotion
> > ShutDownSlotSync() is just before setting this flag and the user has
> > invoked pg_sync_replication_slots() and passed this check but still
> > didn't set the SlotSyncCtx->syncing flag. So, now, the promotion would
> > recognize that there is slot sync going on in parallel, and slot sync
> > wouldn't know that the promotion is in progress.
>
> Did you mean that now, the promotion *would not* recognize...
>

Right.

> I see, I will fix this.
>

Thanks.

--
With Regards,
Amit Kapila.