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

On Sat, Feb 8, 2025 at 12:28 PM Zhijie Hou (Fujitsu)
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Friday, February 7, 2025 9:06 PM Nisha Moond <nisha(dot)moond412(at)gmail(dot)com> wrote:
> >
> > Attached v72 patches, addressed the above comments as well as Vignesh's
> > comments in [2].
> > - There are no new changes in patch-002.
>
> Thanks for updating the patch, I have few review comments:
>
> 1.
> > InvalidateObsoleteReplicationSlots(ReplicationSlotInvalidationCause cause,
>
> I think the type of first parameter 'cause' is not appropriate anymore since
> it's now a bitmap flag instead of an enum.
>

Changed the type to 'int' and updated the name of 'cause' in both
InvalidateObsoleteReplicationSlots() and
InvalidatePossiblyObsoleteSlot(), as both now use the bitmap flag.

> 2.
> > -StaticAssertDecl(lengthof(SlotInvalidationCauses) == (RS_INVAL_MAX_CAUSES + 1),
> > - "array length mismatch");
> > +#define RS_INVAL_MAX_CAUSES (sizeof(InvalidationCauses) / sizeof(InvalidationCauses[0]))
>
> I'd like to confirm if the current value of the RS_INVAL_MAX_CAUSES is correct.
> Previously, the value is arrary_length - 1, while now it seems equal to the
> arrary_length.
>
> And ISTM we could directly call lengthof() here.
>

Done.

> 3.
>
> + if (cause & RS_INVAL_HORIZON)
> + {
> + if (!SlotIsLogical(s))
> + goto invalidation_marked;
>
> I am not sure if this logic is correct. Even if the slot would not be
> invalidated due to RS_INVAL_HORIZON, we should continue to check other causes.
>

Used goto here since we do not expect RS_INVAL_HORIZON to be combined
with any other "cause" and to keep the pgHead behavior.
However, with the bitflag approach, the code should be future-safe, so
replacing goto in v73 should handle this now.

> Besides, instead of using a goto, I personally prefer to move all these codes
> into a separate function which would return a single invalidation cause.
>

Done.

~~~~
Here are the v73 patches incorporating the comments above and the
subsequent comments from [1].
- patch 002 is rebased on 001 with no new changes.

[1] https://www.postgresql.org/message-id/CAA4eK1K%2BAMtGfD3WRK_ivdAeS-CBOUBKJbr-6ku175P1x%3Dwk4g%40mail.gmail.com

--
Thanks,
Nisha