Revert the addition of GetMaxBackends() and related stuff.

This reverts commits 0147fc7, 4567596, aa64f23, and 5ecd018.
There is no longer agreement that introducing this function
was the right way to address the problem. The consensus now
seems to favor trying to make a correct value for MaxBackends
available to mdules executing their _PG_init() functions.

Nathan Bossart

Discussion: http://postgr.es/m/20220323045229.i23skfscdbvrsuxa@jrouhaud

src/backend/storage/lmgr/deadlock.c

@@ -143,7 +143,6 @@ void
 InitDeadLockChecking(void)
 {
 	MemoryContext oldcxt;
-	int max_backends = GetMaxBackends();
 
 	/* Make sure allocations are permanent */
 	oldcxt = MemoryContextSwitchTo(TopMemoryContext);
@@ -152,16 +151,16 @@ InitDeadLockChecking(void)
 	 * FindLockCycle needs at most MaxBackends entries in visitedProcs[] and
 	 * deadlockDetails[].
 	 */
-	visitedProcs = (PGPROC **) palloc(max_backends * sizeof(PGPROC *));
-	deadlockDetails = (DEADLOCK_INFO *) palloc(max_backends * sizeof(DEADLOCK_INFO));
+	visitedProcs = (PGPROC **) palloc(MaxBackends * sizeof(PGPROC *));
+	deadlockDetails = (DEADLOCK_INFO *) palloc(MaxBackends * sizeof(DEADLOCK_INFO));
 
 	/*
 	 * TopoSort needs to consider at most MaxBackends wait-queue entries, and
 	 * it needn't run concurrently with FindLockCycle.
 	 */
 	topoProcs = visitedProcs;	/* re-use this space */
-	beforeConstraints = (int *) palloc(max_backends * sizeof(int));
-	afterConstraints = (int *) palloc(max_backends * sizeof(int));
+	beforeConstraints = (int *) palloc(MaxBackends * sizeof(int));
+	afterConstraints = (int *) palloc(MaxBackends * sizeof(int));
 
 	/*
 	 * We need to consider rearranging at most MaxBackends/2 wait queues
@@ -170,8 +169,8 @@ InitDeadLockChecking(void)
 	 * MaxBackends total waiters.
 	 */
 	waitOrders = (WAIT_ORDER *)
-		palloc((max_backends / 2) * sizeof(WAIT_ORDER));
-	waitOrderProcs = (PGPROC **) palloc(max_backends * sizeof(PGPROC *));
+		palloc((MaxBackends / 2) * sizeof(WAIT_ORDER));
+	waitOrderProcs = (PGPROC **) palloc(MaxBackends * sizeof(PGPROC *));
 
 	/*
 	 * Allow at most MaxBackends distinct constraints in a configuration. (Is
@@ -181,7 +180,7 @@ InitDeadLockChecking(void)
 	 * limits the maximum recursion depth of DeadLockCheckRecurse. Making it
 	 * really big might potentially allow a stack-overflow problem.
 	 */
-	maxCurConstraints = max_backends;
+	maxCurConstraints = MaxBackends;
 	curConstraints = (EDGE *) palloc(maxCurConstraints * sizeof(EDGE));
 
 	/*
@@ -192,7 +191,7 @@ InitDeadLockChecking(void)
 	 * last MaxBackends entries in possibleConstraints[] are reserved as
 	 * output workspace for FindLockCycle.
 	 */
-	maxPossibleConstraints = max_backends * 4;
+	maxPossibleConstraints = MaxBackends * 4;
 	possibleConstraints =
 		(EDGE *) palloc(maxPossibleConstraints * sizeof(EDGE));
 
@@ -328,7 +327,7 @@ DeadLockCheckRecurse(PGPROC *proc)
 	if (nCurConstraints >= maxCurConstraints)
 		return true;			/* out of room for active constraints? */
 	oldPossibleConstraints = nPossibleConstraints;
-	if (nPossibleConstraints + nEdges + GetMaxBackends() <= maxPossibleConstraints)
+	if (nPossibleConstraints + nEdges + MaxBackends <= maxPossibleConstraints)
 	{
 		/* We can save the edge list in possibleConstraints[] */
 		nPossibleConstraints += nEdges;
@@ -389,7 +388,7 @@ TestConfiguration(PGPROC *startProc)
 	/*
 	 * Make sure we have room for FindLockCycle's output.
 	 */
-	if (nPossibleConstraints + GetMaxBackends() > maxPossibleConstraints)
+	if (nPossibleConstraints + MaxBackends > maxPossibleConstraints)
 		return -1;
 
 	/*
@@ -487,7 +486,7 @@ FindLockCycleRecurse(PGPROC *checkProc,
 				 * record total length of cycle --- outer levels will now fill
 				 * deadlockDetails[]
 				 */
-				Assert(depth <= GetMaxBackends());
+				Assert(depth <= MaxBackends);
 				nDeadlockDetails = depth;
 
 				return true;
@@ -501,7 +500,7 @@ FindLockCycleRecurse(PGPROC *checkProc,
 		}
 	}
 	/* Mark proc as seen */
-	Assert(nVisitedProcs < GetMaxBackends());
+	Assert(nVisitedProcs < MaxBackends);
 	visitedProcs[nVisitedProcs++] = checkProc;
 
 	/*
@@ -699,7 +698,7 @@ FindLockCycleRecurseMember(PGPROC *checkProc,
 					/*
 					 * Add this edge to the list of soft edges in the cycle
 					 */
-					Assert(*nSoftEdges < GetMaxBackends());
+					Assert(*nSoftEdges < MaxBackends);
 					softEdges[*nSoftEdges].waiter = checkProcLeader;
 					softEdges[*nSoftEdges].blocker = leader;
 					softEdges[*nSoftEdges].lock = lock;
@@ -772,7 +771,7 @@ FindLockCycleRecurseMember(PGPROC *checkProc,
 					/*
 					 * Add this edge to the list of soft edges in the cycle
 					 */
-					Assert(*nSoftEdges < GetMaxBackends());
+					Assert(*nSoftEdges < MaxBackends);
 					softEdges[*nSoftEdges].waiter = checkProcLeader;
 					softEdges[*nSoftEdges].blocker = leader;
 					softEdges[*nSoftEdges].lock = lock;
@@ -835,7 +834,7 @@ ExpandConstraints(EDGE *constraints,
 		waitOrders[nWaitOrders].procs = waitOrderProcs + nWaitOrderProcs;
 		waitOrders[nWaitOrders].nProcs = lock->waitProcs.size;
 		nWaitOrderProcs += lock->waitProcs.size;
-		Assert(nWaitOrderProcs <= GetMaxBackends());
+		Assert(nWaitOrderProcs <= MaxBackends);
 
 		/*
 		 * Do the topo sort.  TopoSort need not examine constraints after this

src/backend/storage/lmgr/lock.c

@@ -55,7 +55,7 @@
 int			max_locks_per_xact; /* set by guc.c */
 
 #define NLOCKENTS() \
-	mul_size(max_locks_per_xact, add_size(GetMaxBackends(), max_prepared_xacts))
+	mul_size(max_locks_per_xact, add_size(MaxBackends, max_prepared_xacts))
 
 
 /*
@@ -2924,7 +2924,6 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 	LWLock	   *partitionLock;
 	int			count = 0;
 	int			fast_count = 0;
-	int			max_backends = GetMaxBackends();
 
 	if (lockmethodid <= 0 || lockmethodid >= lengthof(LockMethods))
 		elog(ERROR, "unrecognized lock method: %d", lockmethodid);
@@ -2943,12 +2942,12 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 			vxids = (VirtualTransactionId *)
 				MemoryContextAlloc(TopMemoryContext,
 								   sizeof(VirtualTransactionId) *
-								   (max_backends + max_prepared_xacts + 1));
+								   (MaxBackends + max_prepared_xacts + 1));
 	}
 	else
 		vxids = (VirtualTransactionId *)
 			palloc0(sizeof(VirtualTransactionId) *
-					(max_backends + max_prepared_xacts + 1));
+					(MaxBackends + max_prepared_xacts + 1));
 
 	/* Compute hash code and partition lock, and look up conflicting modes. */
 	hashcode = LockTagHashCode(locktag);
@@ -3105,7 +3104,7 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 
 	LWLockRelease(partitionLock);
 
-	if (count > max_backends + max_prepared_xacts)	/* should never happen */
+	if (count > MaxBackends + max_prepared_xacts)	/* should never happen */
 		elog(PANIC, "too many conflicting locks found");
 
 	vxids[count].backendId = InvalidBackendId;
@@ -3652,12 +3651,11 @@ GetLockStatusData(void)
 	int			els;
 	int			el;
 	int			i;
-	int			max_backends = GetMaxBackends();
 
 	data = (LockData *) palloc(sizeof(LockData));
 
 	/* Guess how much space we'll need. */
-	els = max_backends;
+	els = MaxBackends;
 	el = 0;
 	data->locks = (LockInstanceData *) palloc(sizeof(LockInstanceData) * els);
 
@@ -3691,7 +3689,7 @@ GetLockStatusData(void)
 
 			if (el >= els)
 			{
-				els += max_backends;
+				els += MaxBackends;
 				data->locks = (LockInstanceData *)
 					repalloc(data->locks, sizeof(LockInstanceData) * els);
 			}
@@ -3723,7 +3721,7 @@ GetLockStatusData(void)
 
 			if (el >= els)
 			{
-				els += max_backends;
+				els += MaxBackends;
 				data->locks = (LockInstanceData *)
 					repalloc(data->locks, sizeof(LockInstanceData) * els);
 			}
@@ -3852,7 +3850,7 @@ GetBlockerStatusData(int blocked_pid)
 	 * for the procs[] array; the other two could need enlargement, though.)
 	 */
 	data->nprocs = data->nlocks = data->npids = 0;
-	data->maxprocs = data->maxlocks = data->maxpids = GetMaxBackends();
+	data->maxprocs = data->maxlocks = data->maxpids = MaxBackends;
 	data->procs = (BlockedProcData *) palloc(sizeof(BlockedProcData) * data->maxprocs);
 	data->locks = (LockInstanceData *) palloc(sizeof(LockInstanceData) * data->maxlocks);
 	data->waiter_pids = (int *) palloc(sizeof(int) * data->maxpids);
@@ -3927,7 +3925,6 @@ GetSingleProcBlockerStatusData(PGPROC *blocked_proc, BlockedProcsData *data)
 	PGPROC	   *proc;
 	int			queue_size;
 	int			i;
-	int			max_backends = GetMaxBackends();
 
 	/* Nothing to do if this proc is not blocked */
 	if (theLock == NULL)
@@ -3956,7 +3953,7 @@ GetSingleProcBlockerStatusData(PGPROC *blocked_proc, BlockedProcsData *data)
 
 		if (data->nlocks >= data->maxlocks)
 		{
-			data->maxlocks += max_backends;
+			data->maxlocks += MaxBackends;
 			data->locks = (LockInstanceData *)
 				repalloc(data->locks, sizeof(LockInstanceData) * data->maxlocks);
 		}
@@ -3985,7 +3982,7 @@ GetSingleProcBlockerStatusData(PGPROC *blocked_proc, BlockedProcsData *data)
 
 	if (queue_size > data->maxpids - data->npids)
 	{
-		data->maxpids = Max(data->maxpids + max_backends,
+		data->maxpids = Max(data->maxpids + MaxBackends,
 							data->npids + queue_size);
 		data->waiter_pids = (int *) repalloc(data->waiter_pids,
 											 sizeof(int) * data->maxpids);

src/backend/storage/lmgr/predicate.c

@@ -257,7 +257,7 @@
 	(&MainLWLockArray[PREDICATELOCK_MANAGER_LWLOCK_OFFSET + (i)].lock)
 
 #define NPREDICATELOCKTARGETENTS() \
-	mul_size(max_predicate_locks_per_xact, add_size(GetMaxBackends(), max_prepared_xacts))
+	mul_size(max_predicate_locks_per_xact, add_size(MaxBackends, max_prepared_xacts))
 
 #define SxactIsOnFinishedList(sxact) (!SHMQueueIsDetached(&((sxact)->finishedLink)))
 
@@ -1222,7 +1222,7 @@ InitPredicateLocks(void)
 	 * Compute size for serializable transaction hashtable. Note these
 	 * calculations must agree with PredicateLockShmemSize!
 	 */
-	max_table_size = (GetMaxBackends() + max_prepared_xacts);
+	max_table_size = (MaxBackends + max_prepared_xacts);
 
 	/*
 	 * Allocate a list to hold information on transactions participating in
@@ -1375,7 +1375,7 @@ PredicateLockShmemSize(void)
 	size = add_size(size, size / 10);
 
 	/* transaction list */
-	max_table_size = GetMaxBackends() + max_prepared_xacts;
+	max_table_size = MaxBackends + max_prepared_xacts;
 	max_table_size *= 10;
 	size = add_size(size, PredXactListDataSize);
 	size = add_size(size, mul_size((Size) max_table_size,
@@ -1907,7 +1907,7 @@ GetSerializableTransactionSnapshotInt(Snapshot snapshot,
 	{
 		++(PredXact->WritableSxactCount);
 		Assert(PredXact->WritableSxactCount <=
-			   (GetMaxBackends() + max_prepared_xacts));
+			   (MaxBackends + max_prepared_xacts));
 	}
 
 	MySerializableXact = sxact;
@@ -5111,7 +5111,7 @@ predicatelock_twophase_recover(TransactionId xid, uint16 info,
 		{
 			++(PredXact->WritableSxactCount);
 			Assert(PredXact->WritableSxactCount <=
-				   (GetMaxBackends() + max_prepared_xacts));
+				   (MaxBackends + max_prepared_xacts));
 		}
 
 		/*

src/backend/storage/lmgr/proc.c

@@ -103,7 +103,7 @@ ProcGlobalShmemSize(void)
 {
 	Size		size = 0;
 	Size		TotalProcs =
-	add_size(GetMaxBackends(), add_size(NUM_AUXILIARY_PROCS, max_prepared_xacts));
+	add_size(MaxBackends, add_size(NUM_AUXILIARY_PROCS, max_prepared_xacts));
 
 	/* ProcGlobal */
 	size = add_size(size, sizeof(PROC_HDR));
@@ -127,7 +127,7 @@ ProcGlobalSemas(void)
 	 * We need a sema per backend (including autovacuum), plus one for each
 	 * auxiliary process.
 	 */
-	return GetMaxBackends() + NUM_AUXILIARY_PROCS;
+	return MaxBackends + NUM_AUXILIARY_PROCS;
 }
 
 /*
@@ -162,8 +162,7 @@ InitProcGlobal(void)
 	int			i,
 				j;
 	bool		found;
-	int			max_backends = GetMaxBackends();
-	uint32		TotalProcs = max_backends + NUM_AUXILIARY_PROCS + max_prepared_xacts;
+	uint32		TotalProcs = MaxBackends + NUM_AUXILIARY_PROCS + max_prepared_xacts;
 
 	/* Create the ProcGlobal shared structure */
 	ProcGlobal = (PROC_HDR *)
@@ -196,7 +195,7 @@ InitProcGlobal(void)
 	MemSet(procs, 0, TotalProcs * sizeof(PGPROC));
 	ProcGlobal->allProcs = procs;
 	/* XXX allProcCount isn't really all of them; it excludes prepared xacts */
-	ProcGlobal->allProcCount = max_backends + NUM_AUXILIARY_PROCS;
+	ProcGlobal->allProcCount = MaxBackends + NUM_AUXILIARY_PROCS;
 
 	/*
 	 * Allocate arrays mirroring PGPROC fields in a dense manner. See
@@ -222,7 +221,7 @@ InitProcGlobal(void)
 		 * dummy PGPROCs don't need these though - they're never associated
 		 * with a real process
 		 */
-		if (i < max_backends + NUM_AUXILIARY_PROCS)
+		if (i < MaxBackends + NUM_AUXILIARY_PROCS)
 		{
 			procs[i].sem = PGSemaphoreCreate();
 			InitSharedLatch(&(procs[i].procLatch));
@@ -259,7 +258,7 @@ InitProcGlobal(void)
 			ProcGlobal->bgworkerFreeProcs = &procs[i];
 			procs[i].procgloballist = &ProcGlobal->bgworkerFreeProcs;
 		}
-		else if (i < max_backends)
+		else if (i < MaxBackends)
 		{
 			/* PGPROC for walsender, add to walsenderFreeProcs list */
 			procs[i].links.next = (SHM_QUEUE *) ProcGlobal->walsenderFreeProcs;
@@ -287,8 +286,8 @@ InitProcGlobal(void)
 	 * Save pointers to the blocks of PGPROC structures reserved for auxiliary
 	 * processes and prepared transactions.
 	 */
-	AuxiliaryProcs = &procs[max_backends];
-	PreparedXactProcs = &procs[max_backends + NUM_AUXILIARY_PROCS];
+	AuxiliaryProcs = &procs[MaxBackends];
+	PreparedXactProcs = &procs[MaxBackends + NUM_AUXILIARY_PROCS];
 
 	/* Create ProcStructLock spinlock, too */
 	ProcStructLock = (slock_t *) ShmemAlloc(sizeof(slock_t));