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

On Mon, Jan 27, 2025 at 4:20 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Mon, Jan 27, 2025 at 11:00 AM Nisha Moond <nisha(dot)moond412(at)gmail(dot)com> wrote:
> >
> > I discussed the above comments further with Peter off-list, and here
> > are the v63 patches with the following changes:
> > patch-001: The Assert and related comments have been updated for clarity.
> >
>
> The 0001 patch should be discussed in a separate thread as those are
> general improvements that are useful even without the main patch we
> are trying to achieve in this thread. I suggest we break it into three
> patches (a) Ensure the same inactive_since time for all slots, (b)
> Raise an error for invalid slots during ReplicationSlotAcquire(); tell
> in the commit message, without this patch when such an ERROR would
> have otherwise occurred, and (c) Changes in
> InvalidatePossiblyObsoleteSlot(), I suggest to leave this change for
> later as this impacts the core logic of invalidation.
>

I have started a new thread for these general improvements and have
separated the changes (a) and (b) into different patches.

You can find the new thread at [1].

> *
> @@ -812,7 +823,7 @@ ReplicationSlotAlter(const char *name, const bool *failover,
> Assert(MyReplicationSlot == NULL);
> Assert(failover || two_phase);
>
> - ReplicationSlotAcquire(name, false);
> + ReplicationSlotAcquire(name, false, false);
>
> Why don't we want to give ERROR during Alter? I think it is okay to
> not give ERROR for invalid slots during Drop as we are anyway removing
> such slots.
>

Because ReplicationSlotAlter() already handles errors immediately
after acquiring the slot. It raises errors for invalidated slots and
also raises a different error message if the slot is a physical one.
So, In case of ALTER, I feel it is okay to acquire the slot first
without raising errors and then handle errors in the pre-defined way.
Similar immediate error handling is not available at other places.

[1] https://www.postgresql.org/message-id/CABdArM6pBL5hPnSQ%2B5nEVMANcF4FCH7LQmgskXyiLY75TMnKpw%40mail.gmail.com

--
Thanks,
Nisha