Re: Introduce XID age and inactive timeout based replication slot invalidation

On Tue, Feb 6, 2024 at 2:16 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> > Thoughts?
> >
> +1 for the idea, here are some comments on 0002, I will review other
> patches soon and respond.

Thanks for looking at it.

> + <structfield>inactive_at</structfield> <type>timestamptz</type>
>
> Maybe we can change the field name to 'last_inactive_at'? or maybe the
> comment can explain timestampt at which slot was last inactivated.
> I think since we are already maintaining the inactive_count so better
> to explicitly say this is the last invaliding time.

last_inactive_at looks better, so will use that in the next version of
the patch.

> 2.
> + /*
> + * XXX: Can inactive_count of type uint64 ever overflow? It takes
> + * about a half-billion years for inactive_count to overflow even
> + * if slot becomes inactive for every 1 millisecond. So, using
> + * pg_add_u64_overflow might be an overkill.
> + */
>
> Correct we don't need to use pg_add_u64_overflow for this counter.

Will remove this comment in the next version of the patch.

> + /* Convert to numeric. */
> + snprintf(buf, sizeof buf, UINT64_FORMAT, slot_contents.data.inactive_count);
> + values[i++] = DirectFunctionCall3(numeric_in,
> + CStringGetDatum(buf),
> + ObjectIdGetDatum(0),
> + Int32GetDatum(-1));
>
> What is the purpose of doing this? I mean inactive_count is 8 byte
> integer and you can define function outparameter as 'int8' which is 8
> byte integer. Then you don't need to convert int to string and then
> to numeric?

Nope, it's of type uint64, so reporting it as numeric is a way
typically used elsewhere - see code around /* Convert to numeric. */.

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