Refactor GetLockStatusData() to skip backends/groups without fast-path locks.

Previously, GetLockStatusData() checked all slots for every backend
to gather fast-path lock data, which could be inefficient. This commit
refactors it by skipping backends with PID=0 (since they don't hold
fast-path locks) and skipping groups with no registered fast-path locks,
improving efficiency.

This refactoring is particularly beneficial, for example when
max_connections and max_locks_per_transaction are set high,
as it reduces unnecessary checks across numerous slots.

Author: Fujii Masao
Reviewed-by: Bertrand Drouvot
Discussion: https://postgr.es/m/a0a00c44-31e9-4c67-9846-fb9636213ac9@oss.nttdata.com

Author: MasaoFujii

src/backend/storage/lmgr/lock.c

@@ -3731,44 +3731,55 @@ GetLockStatusData(void)
 	for (i = 0; i < ProcGlobal->allProcCount; ++i)
 	{
 		PGPROC	   *proc = &ProcGlobal->allProcs[i];
-		uint32		f;
+
+		/* Skip backends with pid=0, as they don't hold fast-path locks */
+		if (proc->pid == 0)
+			continue;
 
 		LWLockAcquire(&proc->fpInfoLock, LW_SHARED);
 
-		for (f = 0; f < FP_LOCK_SLOTS_PER_BACKEND; ++f)
+		for (uint32 g = 0; g < FastPathLockGroupsPerBackend; g++)
 		{
-			LockInstanceData *instance;
-			uint32		lockbits = FAST_PATH_GET_BITS(proc, f);
-
-			/* Skip unallocated slots. */
-			if (!lockbits)
+			/* Skip groups without registered fast-path locks */
+			if (proc->fpLockBits[g] == 0)
 				continue;
 
-			if (el >= els)
+			for (int j = 0; j < FP_LOCK_SLOTS_PER_GROUP; j++)
 			{
-				els += MaxBackends;
-				data->locks = (LockInstanceData *)
-					repalloc(data->locks, sizeof(LockInstanceData) * els);
-			}
+				LockInstanceData *instance;
+				uint32		f = FAST_PATH_SLOT(g, j);
+				uint32		lockbits = FAST_PATH_GET_BITS(proc, f);
 
-			instance = &data->locks[el];
-			SET_LOCKTAG_RELATION(instance->locktag, proc->databaseId,
-								 proc->fpRelId[f]);
-			instance->holdMask = lockbits << FAST_PATH_LOCKNUMBER_OFFSET;
-			instance->waitLockMode = NoLock;
-			instance->vxid.procNumber = proc->vxid.procNumber;
-			instance->vxid.localTransactionId = proc->vxid.lxid;
-			instance->pid = proc->pid;
-			instance->leaderPid = proc->pid;
-			instance->fastpath = true;
+				/* Skip unallocated slots */
+				if (!lockbits)
+					continue;
 
-			/*
-			 * Successfully taking fast path lock means there were no
-			 * conflicting locks.
-			 */
-			instance->waitStart = 0;
+				if (el >= els)
+				{
+					els += MaxBackends;
+					data->locks = (LockInstanceData *)
+						repalloc(data->locks, sizeof(LockInstanceData) * els);
+				}
 
-			el++;
+				instance = &data->locks[el];
+				SET_LOCKTAG_RELATION(instance->locktag, proc->databaseId,
+									 proc->fpRelId[f]);
+				instance->holdMask = lockbits << FAST_PATH_LOCKNUMBER_OFFSET;
+				instance->waitLockMode = NoLock;
+				instance->vxid.procNumber = proc->vxid.procNumber;
+				instance->vxid.localTransactionId = proc->vxid.lxid;
+				instance->pid = proc->pid;
+				instance->leaderPid = proc->pid;
+				instance->fastpath = true;
+
+				/*
+				 * Successfully taking fast path lock means there were no
+				 * conflicting locks.
+				 */
+				instance->waitStart = 0;
+
+				el++;
+			}
 		}
 
 		if (proc->fpVXIDLock)