Some refinement for the "fast path" lock patch.

1. In GetLockStatusData, avoid initializing instance before we've ensured
that the array is large enough.  Otherwise, if repalloc moves the block
around, we're hosed.

2. Add the word "Relation" to the name of some identifiers, to avoid
assuming that the fast-path mechanism will only ever apply to relations
(though these particular parts certainly will).  Some of the macros
could possibly use similar treatment, but the names are getting awfully
long already.

3. Add a missing word to comment in AtPrepare_Locks().

Author: robertmhaas

src/backend/storage/lmgr/lock.c

@@ -155,11 +155,11 @@ static int			FastPathLocalUseCount = 0;
 #define FastPathStrongMode(mode)	((mode) > ShareUpdateExclusiveLock)
 #define FastPathRelevantMode(mode)	((mode) != ShareUpdateExclusiveLock)
 
-static bool FastPathGrantLock(Oid relid, LOCKMODE lockmode);
-static bool FastPathUnGrantLock(Oid relid, LOCKMODE lockmode);
-static bool FastPathTransferLocks(LockMethod lockMethodTable,
+static bool FastPathGrantRelationLock(Oid relid, LOCKMODE lockmode);
+static bool FastPathUnGrantRelationLock(Oid relid, LOCKMODE lockmode);
+static bool FastPathTransferRelationLocks(LockMethod lockMethodTable,
 					  const LOCKTAG *locktag, uint32 hashcode);
-static PROCLOCK *FastPathGetLockEntry(LOCALLOCK *locallock);
+static PROCLOCK *FastPathGetRelationLockEntry(LOCALLOCK *locallock);
 
 /*
  * To make the fast-path lock mechanism work, we must have some way of
@@ -186,9 +186,9 @@ typedef struct
 {
 	slock_t mutex;
 	uint32 count[FAST_PATH_STRONG_LOCK_HASH_PARTITIONS];
-} FastPathStrongLockData;
+} FastPathStrongRelationLockData;
 
-FastPathStrongLockData *FastPathStrongLocks;
+FastPathStrongRelationLockData *FastPathStrongRelationLocks;
 
 #ifndef LOCK_DEBUG
 static bool Dummy_trace = false;
@@ -415,10 +415,11 @@ InitLocks(void)
 	/*
 	 * Allocate fast-path structures.
 	 */
-	FastPathStrongLocks = ShmemInitStruct("Fast Path Strong Lock Data",
-		sizeof(FastPathStrongLockData), &found);
+	FastPathStrongRelationLocks =
+		ShmemInitStruct("Fast Path Strong Relation Lock Data",
+		sizeof(FastPathStrongRelationLockData), &found);
 	if (!found)
-		SpinLockInit(&FastPathStrongLocks->mutex);
+		SpinLockInit(&FastPathStrongRelationLocks->mutex);
 
 	/*
 	 * Allocate non-shared hash table for LOCALLOCK structs.  This stores lock
@@ -720,10 +721,11 @@ LockAcquireExtended(const LOCKTAG *locktag,
 			 * yet to begin to transfer fast-path locks.
 			 */
 			LWLockAcquire(MyProc->backendLock, LW_EXCLUSIVE);
-			if (FastPathStrongLocks->count[fasthashcode] != 0)
+			if (FastPathStrongRelationLocks->count[fasthashcode] != 0)
 				acquired = false;
 			else
-				acquired = FastPathGrantLock(locktag->locktag_field2, lockmode);
+				acquired = FastPathGrantRelationLock(locktag->locktag_field2,
+													 lockmode);
 			LWLockRelease(MyProc->backendLock);
 			if (acquired)
 			{
@@ -742,11 +744,12 @@ LockAcquireExtended(const LOCKTAG *locktag,
 			 * instruction here, on architectures where that is supported.
 			 */
 			Assert(locallock->holdsStrongLockCount == FALSE);
-			SpinLockAcquire(&FastPathStrongLocks->mutex);
-			FastPathStrongLocks->count[fasthashcode]++;
+			SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
+			FastPathStrongRelationLocks->count[fasthashcode]++;
 			locallock->holdsStrongLockCount = TRUE;
-			SpinLockRelease(&FastPathStrongLocks->mutex);
-			if (!FastPathTransferLocks(lockMethodTable, locktag, hashcode))
+			SpinLockRelease(&FastPathStrongRelationLocks->mutex);
+			if (!FastPathTransferRelationLocks(lockMethodTable, locktag,
+											   hashcode))
 			{
 				if (reportMemoryError)
 					ereport(ERROR,
@@ -1099,11 +1102,11 @@ RemoveLocalLock(LOCALLOCK *locallock)
 		uint32	fasthashcode;
 		fasthashcode = FastPathStrongLockHashPartition(locallock->hashcode);
 
-		SpinLockAcquire(&FastPathStrongLocks->mutex);
-		Assert(FastPathStrongLocks->count[fasthashcode] > 0);
-		FastPathStrongLocks->count[fasthashcode]--;
+		SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
+		Assert(FastPathStrongRelationLocks->count[fasthashcode] > 0);
+		FastPathStrongRelationLocks->count[fasthashcode]--;
 		locallock->holdsStrongLockCount = FALSE;
-		SpinLockRelease(&FastPathStrongLocks->mutex);
+		SpinLockRelease(&FastPathStrongRelationLocks->mutex);
 	}
 	if (!hash_search(LockMethodLocalHash,
 					 (void *) &(locallock->tag),
@@ -1642,7 +1645,8 @@ LockRelease(const LOCKTAG *locktag, LOCKMODE lockmode, bool sessionLock)
 		 * it here.  Another backend may have moved it to the main table.
 		 */
 		LWLockAcquire(MyProc->backendLock, LW_EXCLUSIVE);
-		released = FastPathUnGrantLock(locktag->locktag_field2, lockmode);
+		released = FastPathUnGrantRelationLock(locktag->locktag_field2,
+											   lockmode);
 		LWLockRelease(MyProc->backendLock);
 		if (released)
 		{
@@ -1825,7 +1829,7 @@ LockReleaseAll(LOCKMETHODID lockmethodid, bool allLocks)
 
 			/* Attempt fast-path release. */
 			relid = locallock->tag.lock.locktag_field2;
-			if (FastPathUnGrantLock(relid, lockmode))
+			if (FastPathUnGrantRelationLock(relid, lockmode))
 			{
 				RemoveLocalLock(locallock);
 				continue;
@@ -2117,11 +2121,11 @@ LockReassignCurrentOwner(void)
 }
 
 /*
- * FastPathGrantLock
+ * FastPathGrantRelationLock
  *		Grant lock using per-backend fast-path array, if there is space.
  */
 static bool
-FastPathGrantLock(Oid relid, LOCKMODE lockmode)
+FastPathGrantRelationLock(Oid relid, LOCKMODE lockmode)
 {
 	uint32		f;
 	uint32		unused_slot = FP_LOCK_SLOTS_PER_BACKEND;
@@ -2153,12 +2157,12 @@ FastPathGrantLock(Oid relid, LOCKMODE lockmode)
 }
 
 /*
- * FastPathUnGrantLock
+ * FastPathUnGrantRelationLock
  *		Release fast-path lock, if present.  Update backend-private local
  *		use count, while we're at it.
  */
 static bool
-FastPathUnGrantLock(Oid relid, LOCKMODE lockmode)
+FastPathUnGrantRelationLock(Oid relid, LOCKMODE lockmode)
 {
 	uint32		f;
 	bool		result = false;
@@ -2180,12 +2184,12 @@ FastPathUnGrantLock(Oid relid, LOCKMODE lockmode)
 }
 
 /*
- * FastPathTransferLocks
+ * FastPathTransferRelationLocks
  *		Transfer locks matching the given lock tag from per-backend fast-path
  *		arrays to the shared hash table.
  */
 static bool
-FastPathTransferLocks(LockMethod lockMethodTable, const LOCKTAG *locktag,
+FastPathTransferRelationLocks(LockMethod lockMethodTable, const LOCKTAG *locktag,
 					  uint32 hashcode)
 {
 	LWLockId		partitionLock = LockHashPartitionLock(hashcode);
@@ -2267,7 +2271,7 @@ FastPathTransferLocks(LockMethod lockMethodTable, const LOCKTAG *locktag,
  *      transferring it to the primary lock table if necessary.
  */
 static PROCLOCK *
-FastPathGetLockEntry(LOCALLOCK *locallock)
+FastPathGetRelationLockEntry(LOCALLOCK *locallock)
 {
 	LockMethod		lockMethodTable = LockMethods[DEFAULT_LOCKMETHOD];
 	LOCKTAG		   *locktag = &locallock->tag.lock;
@@ -2650,9 +2654,9 @@ LockRefindAndRelease(LockMethod lockMethodTable, PGPROC *proc,
 		&& FastPathTag(&lock->tag) && FastPathStrongMode(lockmode))
 	{
 		uint32	fasthashcode = FastPathStrongLockHashPartition(hashcode);
-		SpinLockAcquire(&FastPathStrongLocks->mutex);
-		FastPathStrongLocks->count[fasthashcode]--;
-		SpinLockRelease(&FastPathStrongLocks->mutex);
+		SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
+		FastPathStrongRelationLocks->count[fasthashcode]--;
+		SpinLockRelease(&FastPathStrongRelationLocks->mutex);
 	}
 }
 
@@ -2715,11 +2719,11 @@ AtPrepare_Locks(void)
 		/*
 		 * If the local lock was taken via the fast-path, we need to move it
 		 * to the primary lock table, or just get a pointer to the existing
-		 * primary lock table if by chance it's already been transferred.
+		 * primary lock table entry if by chance it's already been transferred.
 		 */
 		if (locallock->proclock == NULL)
 		{
-			locallock->proclock = FastPathGetLockEntry(locallock);
+			locallock->proclock = FastPathGetRelationLockEntry(locallock);
 			locallock->lock = locallock->proclock->tag.myLock;
 		}
 
@@ -3010,7 +3014,7 @@ GetLockStatusData(void)
 
 		for (f = 0; f < FP_LOCK_SLOTS_PER_BACKEND; ++f)
 		{
-			LockInstanceData   *instance = &data->locks[el];
+			LockInstanceData   *instance;
 			uint32		lockbits = FAST_PATH_GET_BITS(proc, f);
 
 			/* Skip unallocated slots. */
@@ -3024,6 +3028,7 @@ GetLockStatusData(void)
 					repalloc(data->locks, sizeof(LockInstanceData) * els);
 			}
 
+			instance = &data->locks[el];
 			SET_LOCKTAG_RELATION(instance->locktag, proc->databaseId,
 								 proc->fpRelId[f]);
 			instance->holdMask = lockbits << FAST_PATH_LOCKNUMBER_OFFSET;
@@ -3455,9 +3460,9 @@ lock_twophase_recover(TransactionId xid, uint16 info,
 	if (FastPathTag(&lock->tag) && FastPathStrongMode(lockmode))
 	{
 		uint32	fasthashcode = FastPathStrongLockHashPartition(hashcode);
-		SpinLockAcquire(&FastPathStrongLocks->mutex);
-		FastPathStrongLocks->count[fasthashcode]++;
-		SpinLockRelease(&FastPathStrongLocks->mutex);
+		SpinLockAcquire(&FastPathStrongRelationLocks->mutex);
+		FastPathStrongRelationLocks->count[fasthashcode]++;
+		SpinLockRelease(&FastPathStrongRelationLocks->mutex);
 	}
 
 	LWLockRelease(partitionLock);