Re: Synchronizing slots from primary to standby

On Mon, Nov 13, 2023 at 11:02 AM Ajin Cherian <itsajin@gmail.com> wrote:
>
> On Thu, Nov 9, 2023 at 9:54 PM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > PFA v32 patches which has below changes:
> Testing with this patch, I see that if the failover enabled slot is
> invalidated on the primary, then the corresponding synced slot is not
> invalidated on the standby. Instead, I see that it continuously gets
> the below error:
> " WARNING:  not synchronizing slot sub; synchronization would move it backwards"
>
> In the code, I see that:
>         if (remote_slot->restart_lsn < MyReplicationSlot->data.restart_lsn)
>         {
>             ereport(WARNING,
>                     errmsg("not synchronizing slot %s; synchronization
> would move"
>                            " it backwards", remote_slot->name));
>
>             ReplicationSlotRelease();
>             CommitTransactionCommand();
>             return;
>         }
>
> If the restart_lsn of the remote slot is behind, then the
> local_slot_update() function is never called to set the invalidation
> status on the local slot. And for invalidated slots, restart_lsn is
> always NULL.
>

Okay. Thanks for testing Ajin. I think it needs a fix wherein we set
the local-slot's invalidation status (provided it is not invalidated
already) from the remote slot before this check itself. And if the
slot is invalidated locally (either by itself) or by primary_slot
being invalidated, then we should skip the sync. I will fix this in
the next version.

thanks
Shveta