Thread

Re: [PATCH] Release replication slot on error in SQL-callable slot functions

SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com> — 2026-05-25T19:01:37Z

Hi,

On Mon, May 25, 2026 at 2:58 AM shveta malik <shveta.malik@gmail.com> wrote:

> On Mon, May 25, 2026 at 12:42 PM SATYANARAYANA NARLAPURAM
> <satyanarlapuram@gmail.com> wrote:
> >
> > Hi
> >
> > On Fri, May 22, 2026 at 2:16 AM shveta malik <shveta.malik@gmail.com>
> wrote:
> >>
> >> Thanks for reporting the issue. I could reproduce the same issue with
> >> all these as well:
> >>
> >> pg_logical_slot_peek_changes
> >> pg_logical_slot_get_binary_changes
> >> pg_logical_slot_peek_binary_changes
> >
> >
> > Please find the attached v2 patch that addressed these three cases as
> well.
> >
>
> Thank You for addressuing these cases. A few comments:
>
> 1)
>
> +-- Test 2: session remains usable after the error (MyReplicationSlot
> cleared)
>
> It shoudl be part of 'Test 1' itself and thus should not be named as 'Test
> 2'
>
> 2)
> --------
> +-- Test 4: copy_replication_slot with max_replication_slots exceeded.
> +-- We reduce max_replication_slots artificially by filling all remaining
> slots.
> +-- Instead, trigger an error by copying to an already-existing name.
> +DO $$
> +BEGIN
> +    PERFORM pg_copy_logical_replication_slot('regression_slot_t3',
> 'regression_slot_t3');
> +EXCEPTION WHEN OTHERS THEN
> +    RAISE NOTICE 'caught: %', SQLERRM;
> +END;
> +$$;
> +-- The original slot must still exist and be usable
> +SELECT count(*) = 1 AS orig_slot_ok FROM pg_replication_slots
> +    WHERE slot_name = 'regression_slot_t3';
> -----------
>
> I don't think we can hit the Assert with above test (at-least I could
> not). Since creation of slot itself will fail as the slot with
> same-name already exists, MyReplicationSlot will never be set and thus
> Assert will not be hit.  A better testcase will be below which fails
> during LoadOutputPlugin() after slot-creation and MyReplicationSlot is
> set already.
>
> SELECT pg_create_logical_replication_slot('src_slot', 'test_decoding');
>
> DO $$
> BEGIN
> PERFORM pg_copy_logical_replication_slot('src_slot', 'dst_slot',
> false, 'nonexistent_plugin');
> EXCEPTION WHEN others THEN
> RAISE NOTICE 'caught: %', SQLERRM;
> END $$;
>
> SELECT count(*) FROM pg_logical_slot_get_changes('src_slot', NULL, NULL);
>
> 3)
> So overall these are the problematic APIs:
>
> pg_create_logical_replication_slot
> pg_replication_slot_advance
> pg_copy_logical_replication_slot
> pg_logical_slot_peek_binary_changes
> pg_logical_slot_peek_changes
> pg_logical_slot_get_changes
> pg_logical_slot_get_binary_changes
>
> First 3 are are mutually exclusive fixes fow which we have added
> testcases. Last 4 are addressed by fixing common function
> pg_logical_slot_get_changes_guts(). I think we should add a test case
> for at-least any one of these APIs to cover
> pg_logical_slot_get_changes_guts().
>

Thanks for reviewing. Please review the attached v3 patch.

Thanks,
Satya