--- src/backend/access/transam/subtrans.c	Tue Nov 29 14:34:58 2005
***************
*** 110,118 ****
  	if (!TransactionIdIsNormal(xid))
  		return InvalidTransactionId;
  
! 	LWLockAcquire(SubtransControlLock, LW_EXCLUSIVE);
! 
! 	slotno = SimpleLruReadPage(SubTransCtl, pageno, xid);
  	ptr = (TransactionId *) SubTransCtl->shared->page_buffer[slotno];
  	ptr += entryno;
  
--- 110,116 ----
  	if (!TransactionIdIsNormal(xid))
  		return InvalidTransactionId;
  
! 	slotno = SimpleLruReadPage_ReadOnly(SubTransCtl, pageno, xid);
  	ptr = (TransactionId *) SubTransCtl->shared->page_buffer[slotno];
  	ptr += entryno;
  

*** src/backend/access/transam/slru.c.orig	Tue Nov 22 16:06:16 2005
--- src/backend/access/transam/slru.c	Tue Nov 29 14:34:51 2005
***************
*** 352,357 ****
--- 352,395 ----
  }
  
  /*
+  * Find a page in a shared buffer, reading it in if necessary.
+  * The page number must correspond to an already-initialized page.
+  *
+  * The passed-in xid is used only for error reporting, and may be
+  * InvalidTransactionId if no specific xid is associated with the action.
+  *
+  * Return value is the shared-buffer slot number now holding the page.
+  * The buffer's LRU access info is updated.
+  *
+  * Control lock must be held at entry, and will be held at exit.
+  */
+ int
+ SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid)
+ {
+ 	SlruShared	shared = ctl->shared;
+ 	int			slotno;
+ 
+ 	LWLockAcquire(shared->ControlLock, LW_SHARED);
+ 
+ 	/* See if page is already in a buffer */
+ 	for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
+ 	{
+ 		if (shared->page_number[slotno] == pageno &&
+ 			shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
+ 			shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
+ 		{
+ 			shared->page_lru_count[slotno] = 0;
+ 			return slotno;
+ 		}
+ 	}
+ 
+ 	LWLockRelease(shared->ControlLock);
+ 	LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE);
+ 
+ 	return SimpleLruReadPage(ctl, pageno, xid);
+ }
+ 
+ /*
   * Write a page from a shared buffer, if necessary.
   * Does nothing if the specified slot is not dirty.
   *
***************
*** 729,736 ****
  	for (;;)
  	{
  		int			slotno;
! 		int			bestslot = 0;
! 		unsigned int bestcount = 0;
  
  		/* See if page already has a buffer assigned */
  		for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
--- 767,775 ----
  	for (;;)
  	{
  		int			slotno;
! 		int			bestslot;
! 		unsigned int bestcount;
! 		int			best_page_number;
  
  		/* See if page already has a buffer assigned */
  		for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
***************
*** 744,758 ****
  		 * If we find any EMPTY slot, just select that one. Else locate the
  		 * least-recently-used slot that isn't the latest page.
  		 */
  		for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
  		{
  			if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
  				return slotno;
! 			if (shared->page_lru_count[slotno] > bestcount &&
! 				shared->page_number[slotno] != shared->latest_page_number)
  			{
  				bestslot = slotno;
! 				bestcount = shared->page_lru_count[slotno];
  			}
  		}
  
--- 783,808 ----
  		 * If we find any EMPTY slot, just select that one. Else locate the
  		 * least-recently-used slot that isn't the latest page.
  		 */
+ 		bestslot = 0;
+ 		bestcount = 0;
+ 		best_page_number = shared->latest_page_number;
  		for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
  		{
+ 			unsigned int	this_lru_count;
+ 			int			this_page_number;
+ 
  			if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
  				return slotno;
! 			this_lru_count = shared->page_lru_count[slotno];
! 			this_page_number = shared->page_number[slotno];
! 			if ((this_lru_count > bestcount ||
! 				 (this_lru_count == bestcount &&
! 				  ctl->PagePrecedes(this_page_number, best_page_number))) &&
! 				this_page_number != shared->latest_page_number)
  			{
  				bestslot = slotno;
! 				bestcount = this_lru_count;
! 				best_page_number = this_page_number;
  			}
  		}