Implement new 'lightweight lock manager' that's intermediate between

existing lock manager and spinlocks: it understands exclusive vs shared
lock but has few other fancy features.  Replace most uses of spinlocks
with lightweight locks.  All remaining uses of spinlocks have very short
lock hold times (a few dozen instructions), so tweak spinlock backoff
code to work efficiently given this assumption.  All per my proposal on
pghackers 26-Sep-01.

1 files changed, 12 insertions, 15 deletions

diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
index 6b25e0a8011..048080a180f 100644
--- a/src/backend/access/transam/varsup.c
+++ b/src/backend/access/transam/varsup.c
@@ -6,7 +6,7 @@
  * Copyright (c) 2000, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.45 2001/08/25 18:52:41 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.46 2001/09/29 04:02:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -15,16 +15,13 @@
 
 #include "access/clog.h"
 #include "access/transam.h"
+#include "storage/ipc.h"
 #include "storage/proc.h"
 
 
 /* Number of OIDs to prefetch (preallocate) per XLOG write */
 #define VAR_OID_PREFETCH		8192
 
-/* Spinlocks for serializing generation of XIDs and OIDs, respectively */
-SPINLOCK	XidGenLockId;
-SPINLOCK	OidGenLockId;
-
 /* pointer to "variable cache" in shared memory (set up by shmem.c) */
 VariableCache ShmemVariableCache = NULL;
 
@@ -44,7 +41,7 @@ GetNewTransactionId(void)
 	if (AMI_OVERRIDE)
 		return BootstrapTransactionId;
 
-	SpinAcquire(XidGenLockId);
+	LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
 
 	xid = ShmemVariableCache->nextXid;
 
@@ -83,7 +80,7 @@ GetNewTransactionId(void)
 	if (MyProc != (PROC *) NULL)
 		MyProc->xid = xid;
 
-	SpinRelease(XidGenLockId);
+	LWLockRelease(XidGenLock);
 
 	return xid;
 }
@@ -103,9 +100,9 @@ ReadNewTransactionId(void)
 	if (AMI_OVERRIDE)
 		return BootstrapTransactionId;
 
-	SpinAcquire(XidGenLockId);
+	LWLockAcquire(XidGenLock, LW_SHARED);
 	xid = ShmemVariableCache->nextXid;
-	SpinRelease(XidGenLockId);
+	LWLockRelease(XidGenLock);
 
 	return xid;
 }
@@ -122,7 +119,7 @@ GetNewObjectId(void)
 {
 	Oid		result;
 
-	SpinAcquire(OidGenLockId);
+	LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
 
 	/*
 	 * Check for wraparound of the OID counter.  We *must* not return 0
@@ -149,7 +146,7 @@ GetNewObjectId(void)
 	(ShmemVariableCache->nextOid)++;
 	(ShmemVariableCache->oidCount)--;
 
-	SpinRelease(OidGenLockId);
+	LWLockRelease(OidGenLock);
 
 	lastSeenOid = result;
 
@@ -162,12 +159,12 @@ CheckMaxObjectId(Oid assigned_oid)
 	if (lastSeenOid != InvalidOid && assigned_oid < lastSeenOid)
 		return;
 
-	SpinAcquire(OidGenLockId);
+	LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
 
 	if (assigned_oid < ShmemVariableCache->nextOid)
 	{
 		lastSeenOid = ShmemVariableCache->nextOid - 1;
-		SpinRelease(OidGenLockId);
+		LWLockRelease(OidGenLock);
 		return;
 	}
 
@@ -178,7 +175,7 @@ CheckMaxObjectId(Oid assigned_oid)
 		ShmemVariableCache->oidCount -=
 			assigned_oid - ShmemVariableCache->nextOid + 1;
 		ShmemVariableCache->nextOid = assigned_oid + 1;
-		SpinRelease(OidGenLockId);
+		LWLockRelease(OidGenLock);
 		return;
 	}
 
@@ -192,5 +189,5 @@ CheckMaxObjectId(Oid assigned_oid)
 	ShmemVariableCache->nextOid = assigned_oid + 1;
 	ShmemVariableCache->oidCount = VAR_OID_PREFETCH - 1;
 
-	SpinRelease(OidGenLockId);
+	LWLockRelease(OidGenLock);
 }