Re: Deadlock detector fails to activate on a hot standby replica

On Mon, May 25, 2026 at 11:20 PM Vitaly Davydov
<v(dot)davydov(at)postgrespro(dot)ru> wrote:
>
> Dear Fujii Masao,
>
> Thank you for the review of the patch. Based on your comments I propose
> a new version of the patch.

Thanks for updating the patch!

+ if (got_standby_delay_timeout)
+ SendRecoveryConflictWithBufferPin(RECOVERY_CONFLICT_BUFFERPIN);
+ else if (got_standby_deadlock_timeout)
+ {

Shouldn't we break out of the loop when either got_standby_delay_timeout or
got_standby_deadlock_timeout becomes true? Otherwise, the loop continues with
those flags still set, which could cause SendRecoveryConflictWithBufferPin() to
be called unnecessarily in the subsequent cycles.

+ if (BufferGetRefCount(buffer) <= 1)

Should this be "BufferGetRefCount(buffer) == 1" instead? I don't think
BufferGetRefCount(buffer) should ever return 0 here. If that's correct,
would it make sense to explicitly detect that case, for example:

-----------------
uint32 refcount = BufferGetRefCount(buffer);

Assert(refcount > 0);

if (refcount == 0)
elog(ERROR, "buffer refcount dropped to zero while waiting for
cleanup lock");

if (refcount == 1)
break;
-----------------

> I also added a new tap-test as a part of the patch. I did some changes in the
> tap test to make it stable. Let me know, please, if it should be in a separate
> commit.

Do we really need a new TAP test file for this? We already have
a startup/backend deadlock test in t/031_recovery_conflict.pl. Extending
the deadlock section there to cover this test case seems simpler and easier to
follow than introducing a new t/053_* test.

Regards,

--
Fujii Masao