Re: Truncate in synchronous logical replication failed

On Wed, 07 Apr 2021 at 16:34, tanghy(dot)fnst(at)fujitsu(dot)com <tanghy(dot)fnst(at)fujitsu(dot)com> wrote:
> On Wednesday, April 7, 2021 5:28 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote
>
>>Can you please check if the behavior is the same for PG-13? This is
>>just to ensure that we have not introduced any bug in PG-14.
>
> Yes, same failure happens at PG-13, too.
>

I found that when we truncate a table in synchronous logical replication,
LockAcquireExtended() [1] will try to take a lock via fast path and it
failed (FastPathStrongRelationLocks->count[fasthashcode] = 1).
However, it can acquire the lock when in asynchronous logical replication.
I'm not familiar with the locks, any suggestions? What the difference
between sync and async logical replication for locks?

[1]
if (EligibleForRelationFastPath(locktag, lockmode) &&
FastPathLocalUseCount < FP_LOCK_SLOTS_PER_BACKEND)
{
uint32 fasthashcode = FastPathStrongLockHashPartition(hashcode);
bool acquired;

/*
* LWLockAcquire acts as a memory sequencing point, so it's safe to
* assume that any strong locker whose increment to
* FastPathStrongRelationLocks->counts becomes visible after we test
* it has yet to begin to transfer fast-path locks.
*/
LWLockAcquire(&MyProc->fpInfoLock, LW_EXCLUSIVE);
if (FastPathStrongRelationLocks->count[fasthashcode] != 0)
acquired = false;
else
acquired = FastPathGrantRelationLock(locktag->locktag_field2,
lockmode);
LWLockRelease(&MyProc->fpInfoLock);
if (acquired)
{
/*
* The locallock might contain stale pointers to some old shared
* objects; we MUST reset these to null before considering the
* lock to be acquired via fast-path.
*/
locallock->lock = NULL;
locallock->proclock = NULL;
GrantLockLocal(locallock, owner);
return LOCKACQUIRE_OK;
}
}

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.