Index: src/backend/access/transam/xact.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/access/transam/xact.c,v
retrieving revision 1.221
diff -c -r1.221 xact.c
*** src/backend/access/transam/xact.c	20 Jun 2006 22:51:59 -0000	1.221
--- src/backend/access/transam/xact.c	27 Jun 2006 14:59:22 -0000
***************
*** 717,723 ****
  		 */
  		madeTCentries = (MyLastRecPtr.xrecoff != 0);
  		if (madeTCentries)
! 			LWLockAcquire(CheckpointStartLock, LW_SHARED);
  
  		/*
  		 * We only need to log the commit in XLOG if the transaction made any
--- 717,723 ----
  		 */
  		madeTCentries = (MyLastRecPtr.xrecoff != 0);
  		if (madeTCentries)
! 			LWLockAcquire(CheckpointStartLock, LW_SHARED_QUEUED);
  
  		/*
  		 * We only need to log the commit in XLOG if the transaction made any
Index: src/backend/storage/lmgr/lwlock.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/storage/lmgr/lwlock.c,v
retrieving revision 1.39
diff -c -r1.39 lwlock.c
*** src/backend/storage/lmgr/lwlock.c	21 Apr 2006 16:45:12 -0000	1.39
--- src/backend/storage/lmgr/lwlock.c	27 Jun 2006 14:59:23 -0000
***************
*** 362,378 ****
  			lock->releaseOK = true;
  
  		/* If I can get the lock, do so quickly. */
! 		if (mode == LW_EXCLUSIVE)
! 		{
! 			if (lock->exclusive == 0 && lock->shared == 0)
! 			{
! 				lock->exclusive++;
! 				mustwait = false;
! 			}
! 			else
! 				mustwait = true;
! 		}
! 		else
  		{
  			if (lock->exclusive == 0)
  			{
--- 362,368 ----
  			lock->releaseOK = true;
  
  		/* If I can get the lock, do so quickly. */
!         if (mode == LW_SHARED)        
  		{
  			if (lock->exclusive == 0)
  			{
***************
*** 382,387 ****
--- 372,396 ----
  			else
  				mustwait = true;
  		}
+         else
+ 		{
+             if (mode == LW_EXCLUSIVE)           /* LW_EXCLUSIVE */
+     			if (lock->exclusive == 0 && lock->shared == 0)
+     			{
+        				lock->exclusive++;
+     				mustwait = false;
+     			}
+     			else
+     				mustwait = true;
+             else                                /* LW_SHARED_QUEUED */
+     			if (lock->exclusive == 0 && lock->head == NULL)
+     			{
+        				lock->shared++;
+     				mustwait = false;
+     			}
+     			else
+     				mustwait = true;
+ 		}
  
  		if (!mustwait)
  			break;				/* got the lock */
***************
*** 484,500 ****
  	SpinLockAcquire(&lock->mutex);
  
  	/* If I can get the lock, do so quickly. */
! 	if (mode == LW_EXCLUSIVE)
! 	{
! 		if (lock->exclusive == 0 && lock->shared == 0)
! 		{
! 			lock->exclusive++;
! 			mustwait = false;
! 		}
! 		else
! 			mustwait = true;
! 	}
! 	else
  	{
  		if (lock->exclusive == 0)
  		{
--- 493,499 ----
  	SpinLockAcquire(&lock->mutex);
  
  	/* If I can get the lock, do so quickly. */
!     if (mode == LW_SHARED)        
  	{
  		if (lock->exclusive == 0)
  		{
***************
*** 504,509 ****
--- 503,527 ----
  		else
  			mustwait = true;
  	}
+     else
+ 	{
+         if (mode == LW_EXCLUSIVE)           /* LW_EXCLUSIVE */
+ 			if (lock->exclusive == 0 && lock->shared == 0)
+ 			{
+     				lock->exclusive++;
+ 				mustwait = false;
+ 			}
+ 			else
+ 				mustwait = true;
+         else                                /* LW_SHARED_QUEUED */
+ 			if (lock->exclusive == 0 && lock->head == NULL)
+ 			{
+     				lock->shared++;
+ 				mustwait = false;
+ 			}
+ 			else
+ 				mustwait = true;
+ 	}
  
  	/* We are done updating shared state of the lock itself. */
  	SpinLockRelease(&lock->mutex);
***************
*** 622,627 ****
--- 640,646 ----
  }
  
  
+ 
  /*
   * LWLockReleaseAll - release all currently-held locks
   *
Index: src/include/storage/lwlock.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/storage/lwlock.h,v
retrieving revision 1.28
diff -c -r1.28 lwlock.h
*** src/include/storage/lwlock.h	8 May 2006 00:00:17 -0000	1.28
--- src/include/storage/lwlock.h	27 Jun 2006 14:59:24 -0000
***************
*** 57,63 ****
  typedef enum LWLockMode
  {
  	LW_EXCLUSIVE,
! 	LW_SHARED
  } LWLockMode;
  
  
--- 57,64 ----
  typedef enum LWLockMode
  {
  	LW_EXCLUSIVE,
! 	LW_SHARED,
!     LW_SHARED_QUEUED
  } LWLockMode;