Re: Allow logical failover slots to wait on synchronous replication

Hi John,

On Thu, Jul 18, 2024 at 02:22:08PM -0700, John H wrote:
> Hi Bertrand,
> 
> > 1 ===
> > ...
> > That's worth additional comments in the code.
> 
> There's this comment already about caching the value already, not sure
> if you prefer something more?
> 
> /* Cache values to reduce contention on lock */

Yeah, at the same place as the static lsn[] declaration, something like:

static XLogRecPtr       lsn[NUM_SYNC_REP_WAIT_MODE]; /* cached LSNs */

but that may just be a matter of taste.

> > 3 ===
> > ...
> > NUM_SYNC_REP_WAIT_MODE is small but as the goal is the keep the lock time as
> > short as possible I wonder if it wouldn't be better to use memcpy() here instead
> > of this for loop.
> >
> 
> It results in a "Wdiscarded-qualifiers" which is safe given we take
> the lock, but adds noise?
> What do you think?
> 
> "slot.c:2756:46: warning: passing argument 2 of ‘memcpy’ discards
> ‘volatile’ qualifier from pointer target type
> [-Wdiscarded-qualifiers]"

Right, we may want to cast it then but given that the for loop is "small" I think
that's also fine to keep the for loop.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com