Re: Synchronizing slots from primary to standby

Hi,

On Mon, Feb 26, 2024 at 05:52:40PM +0530, shveta malik wrote:
> On Mon, Feb 26, 2024 at 5:18 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > > > > + if (!ok)
> > > > > + GUC_check_errdetail("List syntax is invalid.");
> > > > > +
> > > > > + /*
> > > > > + * If there is a syntax error in the name or if the replication slots'
> > > > > + * data is not initialized yet (i.e., we are in the startup process), skip
> > > > > + * the slot verification.
> > > > > + */
> > > > > + if (!ok || !ReplicationSlotCtl)
> > > > > + {
> > > > > + pfree(rawname);
> > > > > + list_free(elemlist);
> > > > > + return ok;
> > > > > + }
> > > > >
> > > > > we are testing the "ok" value twice, what about using if...else if... instead and
> > > > > test it once? If so, it might be worth to put the:
> > > > >
> > > > > "
> > > > > + pfree(rawname);
> > > > > + list_free(elemlist);
> > > > > + return ok;
> > > > > "
> > > > >
> > > > > in a "goto".
> > > >
> > > > There were comments to remove the 'goto' statement and avoid
> > > > duplicate free code, so I prefer the current style.
> > >
> > > The duplicate free code would come from the if...else if... rewrite but then
> > > the "goto" would remove it, so I'm not sure to understand your point.
> > >
> >
> > I think Hou-San wants to say that there was previously a comment to
> > remove goto and now you are saying to introduce it. But, I think we
> > can avoid both code duplication and goto, if the first thing we check
> > in the function is ReplicationSlotCtl and return false if the same is
> > not set. Won't that be better?
>
> I think we can not do that as we need to check atleast syntax before
> we return due to NULL ReplicationSlotCtl. We get NULL
> ReplicationSlotCtl during instance startup in
> check_standby_slot_names() as postmaster first loads GUC-table and
> then initializes shared-memory for replication slots. See calls of
> InitializeGUCOptions() and CreateSharedMemoryAndSemaphores() in
> PostmasterMain(). FWIW, I do not have any issue with current code as
> well, but if we have to change it, is [1] any better?
>
> [1]:
> check_standby_slot_names()
> {
> ....
> if (!ok)
> {
> GUC_check_errdetail("List syntax is invalid.");
> }
> else if (ReplicationSlotCtl)
> {
> foreach-loop for slot validation
> }
>
> pfree(rawname);
> list_free(elemlist);
> return ok;
> }
>

Yeah thanks, it does not test the "ok" value twice and get rid of the goto
while checking the syntax first: I'd vote for it.

Regards,

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