Re: Truncate in synchronous logical replication failed

On Wed, 07 Apr 2021 at 16:34, tanghy.fnst@fujitsu.com <tanghy.fnst@fujitsu.com> wrote:
> On Wednesday, April 7, 2021 5:28 PM Amit Kapila <amit.kapila16@gmail.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.