diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index c1c5d64ea2..47564a3002 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.265 2003/11/12 21:15:51 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.266 2003/11/13 00:40:00 wieck Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -33,6 +33,7 @@
 #include "commands/vacuum.h"
 #include "executor/executor.h"
 #include "miscadmin.h"
+#include "storage/buf_internals.h"
 #include "storage/freespace.h"
 #include "storage/sinval.h"
 #include "storage/smgr.h"
@@ -310,8 +311,16 @@ vacuum(VacuumStmt *vacstmt)
 			else
 				old_context = MemoryContextSwitchTo(anl_context);
 
+			/*
+			 * Tell the buffer replacement strategy that vacuum is
+			 * causing the IO
+			 */
+			StrategyHintVacuum(true);
+
 			analyze_rel(relid, vacstmt);
 
+			StrategyHintVacuum(false);
+
 			if (vacstmt->vacuum)
 				CommitTransactionCommand();
 			else
@@ -749,6 +758,12 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	SetQuerySnapshot();			/* might be needed for functions in
 								 * indexes */
 
+	/*
+	 * Tell the cache replacement strategy that vacuum is causing
+	 * all following IO
+	 */
+	StrategyHintVacuum(true);
+
 	/*
 	 * Check for user-requested abort.	Note we want this to be inside a
 	 * transaction, so xact.c doesn't issue useless WARNING.
@@ -763,6 +778,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 							  ObjectIdGetDatum(relid),
 							  0, 0, 0))
 	{
+		StrategyHintVacuum(false);
 		CommitTransactionCommand();
 		return true;			/* okay 'cause no data there */
 	}
@@ -796,6 +812,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 				(errmsg("skipping \"%s\" --- only table or database owner can vacuum it",
 						RelationGetRelationName(onerel))));
 		relation_close(onerel, lmode);
+		StrategyHintVacuum(false);
 		CommitTransactionCommand();
 		return false;
 	}
@@ -810,6 +827,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 				(errmsg("skipping \"%s\" --- cannot vacuum indexes, views, or special system tables",
 						RelationGetRelationName(onerel))));
 		relation_close(onerel, lmode);
+		StrategyHintVacuum(false);
 		CommitTransactionCommand();
 		return false;
 	}
@@ -824,6 +842,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	if (isOtherTempNamespace(RelationGetNamespace(onerel)))
 	{
 		relation_close(onerel, lmode);
+		StrategyHintVacuum(false);
 		CommitTransactionCommand();
 		return true;			/* assume no long-lived data in temp
 								 * tables */
@@ -863,6 +882,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	/*
 	 * Complete the transaction and free all temporary memory used.
 	 */
+	StrategyHintVacuum(false);
 	CommitTransactionCommand();
 
 	/*
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 38cc332efd..616338c60c 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/buf_init.c,v 1.54 2003/08/04 02:40:03 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/buf_init.c,v 1.55 2003/11/13 00:40:01 wieck Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -48,9 +48,6 @@ long	   *CurTraceBuf;
 int			ShowPinTrace = 0;
 
 int			Data_Descriptors;
-int			Free_List_Descriptor;
-int			Lookup_List_Descriptor;
-int			Num_Descriptors;
 
 BufferDesc *BufferDescriptors;
 Block	   *BufferBlockPointers;
@@ -133,9 +130,6 @@ InitBufferPool(void)
 	int			i;
 
 	Data_Descriptors = NBuffers;
-	Free_List_Descriptor = Data_Descriptors;
-	Lookup_List_Descriptor = Data_Descriptors + 1;
-	Num_Descriptors = Data_Descriptors + 1;
 
 	/*
 	 * It's probably not really necessary to grab the lock --- if there's
@@ -156,7 +150,7 @@ InitBufferPool(void)
 
 	BufferDescriptors = (BufferDesc *)
 		ShmemInitStruct("Buffer Descriptors",
-					  Num_Descriptors * sizeof(BufferDesc), &foundDescs);
+					  Data_Descriptors * sizeof(BufferDesc), &foundDescs);
 
 	BufferBlocks = (char *)
 		ShmemInitStruct("Buffer Blocks",
@@ -176,16 +170,14 @@ InitBufferPool(void)
 		block = BufferBlocks;
 
 		/*
-		 * link the buffers into a circular, doubly-linked list to
-		 * initialize free list, and initialize the buffer headers. Still
-		 * don't know anything about replacement strategy in this file.
+		 * link the buffers into a single linked list. This will become the
+		 * LiFo list of unused buffers returned by StragegyGetBuffer().
 		 */
 		for (i = 0; i < Data_Descriptors; block += BLCKSZ, buf++, i++)
 		{
 			Assert(ShmemIsValid((unsigned long) block));
 
-			buf->freeNext = i + 1;
-			buf->freePrev = i - 1;
+			buf->bufNext = i + 1;
 
 			CLEAR_BUFFERTAG(&(buf->tag));
 			buf->buf_id = i;
@@ -199,14 +191,12 @@ InitBufferPool(void)
 			buf->wait_backend_id = 0;
 		}
 
-		/* close the circular queue */
-		BufferDescriptors[0].freePrev = Data_Descriptors - 1;
-		BufferDescriptors[Data_Descriptors - 1].freeNext = 0;
+		/* Correct last entry */
+		BufferDescriptors[Data_Descriptors - 1].bufNext = -1;
 	}
 
 	/* Init other shared buffer-management stuff */
-	InitBufTable();
-	InitFreeList(!foundDescs);
+	StrategyInitialize(!foundDescs);
 
 	LWLockRelease(BufMgrLock);
 }
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index 072288e330..a2318a29f3 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/buf_table.c,v 1.29 2003/08/04 02:40:03 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/buf_table.c,v 1.30 2003/11/13 00:40:01 wieck Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -38,7 +38,7 @@ static HTAB *SharedBufHash;
  * Initialize shmem hash table for mapping buffers
  */
 void
-InitBufTable(void)
+InitBufTable(int size)
 {
 	HASHCTL		info;
 
@@ -50,7 +50,7 @@ InitBufTable(void)
 	info.hash = tag_hash;
 
 	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
-								  NBuffers, NBuffers,
+								  size, size,
 								  &info,
 								  HASH_ELEM | HASH_FUNCTION);
 
@@ -58,69 +58,36 @@ InitBufTable(void)
 		elog(FATAL, "could not initialize shared buffer hash table");
 }
 
-BufferDesc *
+/*
+ * BufTableLookup
+ */
+int
 BufTableLookup(BufferTag *tagPtr)
 {
 	BufferLookupEnt *result;
 
 	if (tagPtr->blockNum == P_NEW)
-		return NULL;
+		return -1;
 
 	result = (BufferLookupEnt *)
 		hash_search(SharedBufHash, (void *) tagPtr, HASH_FIND, NULL);
 	if (!result)
-		return NULL;
+		return -1;
 
-	return &(BufferDescriptors[result->id]);
+	return result->id;
 }
 
 /*
  * BufTableDelete
  */
 bool
-BufTableDelete(BufferDesc *buf)
-{
-	BufferLookupEnt *result;
-
-	/*
-	 * buffer not initialized or has been removed from table already.
-	 * BM_DELETED keeps us from removing buffer twice.
-	 */
-	if (buf->flags & BM_DELETED)
-		return TRUE;
-
-	buf->flags |= BM_DELETED;
-
-	result = (BufferLookupEnt *)
-		hash_search(SharedBufHash, (void *) &(buf->tag), HASH_REMOVE, NULL);
-
-	if (!result)				/* shouldn't happen */
-		elog(ERROR, "shared buffer hash table corrupted");
-
-	/*
-	 * Clear the buffer's tag.  This doesn't matter for the hash table,
-	 * since the buffer is already removed from it, but it ensures that
-	 * sequential searches through the buffer table won't think the buffer
-	 * is still valid for its old page.
-	 */
-	buf->tag.rnode.relNode = InvalidOid;
-	buf->tag.rnode.tblNode = InvalidOid;
-
-	return TRUE;
-}
-
-bool
-BufTableInsert(BufferDesc *buf)
+BufTableInsert(BufferTag *tagPtr, Buffer buf_id)
 {
 	BufferLookupEnt *result;
 	bool		found;
 
-	/* cannot insert it twice */
-	Assert(buf->flags & BM_DELETED);
-	buf->flags &= ~(BM_DELETED);
-
 	result = (BufferLookupEnt *)
-		hash_search(SharedBufHash, (void *) &(buf->tag), HASH_ENTER, &found);
+		hash_search(SharedBufHash, (void *) tagPtr, HASH_ENTER, &found);
 
 	if (!result)
 		ereport(ERROR,
@@ -130,7 +97,24 @@ BufTableInsert(BufferDesc *buf)
 	if (found)					/* found something else in the table? */
 		elog(ERROR, "shared buffer hash table corrupted");
 
-	result->id = buf->buf_id;
+	result->id = buf_id;
+	return TRUE;
+}
+
+/*
+ * BufTableDelete
+ */
+bool
+BufTableDelete(BufferTag *tagPtr)
+{
+	BufferLookupEnt *result;
+
+	result = (BufferLookupEnt *)
+		hash_search(SharedBufHash, (void *) tagPtr, HASH_REMOVE, NULL);
+
+	if (!result)				/* shouldn't happen */
+		elog(ERROR, "shared buffer hash table corrupted");
+
 	return TRUE;
 }
 
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index d95129df4e..f10ff7e5b7 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.141 2003/09/25 06:58:01 petere Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.142 2003/11/13 00:40:01 wieck Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -260,12 +260,8 @@ ReadBufferInternal(Relation reln, BlockNumber blockNum,
 	if (status == SM_FAIL)
 	{
 		/* IO Failed.  cleanup the data structures and go home */
+		StrategyInvalidateBuffer(bufHdr);
 
-		if (!BufTableDelete(bufHdr))
-		{
-			LWLockRelease(BufMgrLock);
-			elog(FATAL, "buffer table broken after I/O error");
-		}
 		/* remember that BufferAlloc() pinned the buffer */
 		UnpinBuffer(bufHdr);
 
@@ -318,7 +314,7 @@ BufferAlloc(Relation reln,
 	INIT_BUFFERTAG(&newTag, reln, blockNum);
 
 	/* see if the block is in the buffer pool already */
-	buf = BufTableLookup(&newTag);
+	buf = StrategyBufferLookup(&newTag, false);
 	if (buf != NULL)
 	{
 		/*
@@ -379,7 +375,7 @@ BufferAlloc(Relation reln,
 	inProgress = FALSE;
 	for (buf = (BufferDesc *) NULL; buf == (BufferDesc *) NULL;)
 	{
-		buf = GetFreeBuffer();
+		buf = StrategyGetBuffer();
 
 		/* GetFreeBuffer will abort if it can't find a free buffer */
 		Assert(buf);
@@ -492,7 +488,7 @@ BufferAlloc(Relation reln,
 			 * we haven't gotten around to insert the new tag into the
 			 * buffer table. So we need to check here.		-ay 3/95
 			 */
-			buf2 = BufTableLookup(&newTag);
+			buf2 = StrategyBufferLookup(&newTag, true);
 			if (buf2 != NULL)
 			{
 				/*
@@ -535,29 +531,12 @@ BufferAlloc(Relation reln,
 	 */
 
 	/*
-	 * Change the name of the buffer in the lookup table:
-	 *
-	 * Need to update the lookup table before the read starts. If someone
-	 * comes along looking for the buffer while we are reading it in, we
-	 * don't want them to allocate a new buffer.  For the same reason, we
-	 * didn't want to erase the buf table entry for the buffer we were
-	 * writing back until now, either.
+	 * Tell the buffer replacement strategy that we are replacing the
+	 * buffer content. Then rename the buffer.
 	 */
-
-	if (!BufTableDelete(buf))
-	{
-		LWLockRelease(BufMgrLock);
-		elog(FATAL, "buffer wasn't in the buffer hash table");
-	}
-
+	StrategyReplaceBuffer(buf, reln, blockNum);
 	INIT_BUFFERTAG(&(buf->tag), reln, blockNum);
 
-	if (!BufTableInsert(buf))
-	{
-		LWLockRelease(BufMgrLock);
-		elog(FATAL, "buffer in buffer hash table twice");
-	}
-
 	/*
 	 * Buffer contents are currently invalid.  Have to mark IO IN PROGRESS
 	 * so no one fiddles with them until the read completes.  If this
@@ -709,13 +688,28 @@ BufferSync(void)
 	BufferDesc *bufHdr;
 	ErrorContextCallback errcontext;
 
+	int			num_buffer_dirty;
+	int		   *buffer_dirty;
+
 	/* Setup error traceback support for ereport() */
 	errcontext.callback = buffer_write_error_callback;
 	errcontext.arg = NULL;
 	errcontext.previous = error_context_stack;
 	error_context_stack = &errcontext;
 
-	for (i = 0, bufHdr = BufferDescriptors; i < NBuffers; i++, bufHdr++)
+	/*
+	 * Get a list of all currently dirty buffers and how many there are.
+	 * We do not flush buffers that get dirtied after we started. They
+	 * have to wait until the next checkpoint.
+	 */
+	buffer_dirty = (int *)palloc(NBuffers * sizeof(int));
+	num_buffer_dirty = 0;
+
+	LWLockAcquire(BufMgrLock, LW_EXCLUSIVE);
+	num_buffer_dirty = StrategyDirtyBufferList(buffer_dirty, NBuffers);
+	LWLockRelease(BufMgrLock);
+
+	for (i = 0; i < num_buffer_dirty; i++)
 	{
 		Buffer		buffer;
 		int			status;
@@ -723,10 +717,11 @@ BufferSync(void)
 		XLogRecPtr	recptr;
 		Relation	reln;
 
-		errcontext.arg = bufHdr;
-
 		LWLockAcquire(BufMgrLock, LW_EXCLUSIVE);
 
+		bufHdr = &BufferDescriptors[buffer_dirty[i]];
+		errcontext.arg = bufHdr;
+
 		if (!(bufHdr->flags & BM_VALID))
 		{
 			LWLockRelease(BufMgrLock);
@@ -855,6 +850,8 @@ BufferSync(void)
 			RelationDecrementReferenceCount(reln);
 	}
 
+	pfree(buffer_dirty);
+
 	/* Pop the error context stack */
 	error_context_stack = errcontext.previous;
 }
@@ -959,9 +956,9 @@ AtEOXact_Buffers(bool isCommit)
 
 			if (isCommit)
 				elog(WARNING,
-				"buffer refcount leak: [%03d] (freeNext=%d, freePrev=%d, "
+				"buffer refcount leak: [%03d] (bufNext=%d, "
 				  "rel=%u/%u, blockNum=%u, flags=0x%x, refcount=%d %ld)",
-					 i, buf->freeNext, buf->freePrev,
+					 i, buf->bufNext,
 					 buf->tag.rnode.tblNode, buf->tag.rnode.relNode,
 					 buf->tag.blockNum, buf->flags,
 					 buf->refcount, PrivateRefCount[i]);
@@ -1229,7 +1226,7 @@ recheck:
 			/*
 			 * And mark the buffer as no longer occupied by this rel.
 			 */
-			BufTableDelete(bufHdr);
+			StrategyInvalidateBuffer(bufHdr);
 		}
 	}
 
@@ -1295,7 +1292,7 @@ recheck:
 			/*
 			 * And mark the buffer as no longer occupied by this page.
 			 */
-			BufTableDelete(bufHdr);
+			StrategyInvalidateBuffer(bufHdr);
 		}
 	}
 
@@ -1543,7 +1540,7 @@ FlushRelationBuffers(Relation rel, BlockNumber firstDelBlock)
 				return -2;
 			}
 			if (bufHdr->tag.blockNum >= firstDelBlock)
-				BufTableDelete(bufHdr);
+				StrategyInvalidateBuffer(bufHdr);
 		}
 	}
 
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index 227c7e938d..9e340b4720 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -1,15 +1,14 @@
 /*-------------------------------------------------------------------------
  *
  * freelist.c
- *	  routines for manipulating the buffer pool's replacement strategy
- *	  freelist.
+ *	  routines for manipulating the buffer pool's replacement strategy.
  *
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/freelist.c,v 1.31 2003/08/04 02:40:03 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/freelist.c,v 1.32 2003/11/13 00:40:01 wieck Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -31,55 +30,814 @@
 #include "storage/bufmgr.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
+#include "access/xact.h"
 
+#define STRAT_LIST_UNUSED	-1
+#define STRAT_LIST_B1		0
+#define STRAT_LIST_T1		1
+#define STRAT_LIST_T2		2
+#define STRAT_LIST_B2		3
+#define STRAT_NUM_LISTS		4
 
-static BufferDesc *SharedFreeList;
+#ifndef MAX
+#define MAX(a,b) (((a) > (b)) ? (a) : (b))
+#endif
+#ifndef MIN
+#define MIN(a,b) (((a) < (b)) ? (a) : (b))
+#endif
 
 /*
- * State-checking macros
+ * The Cache Directory Block (CDB) of the Adaptive Replacement Cache (ARC)
  */
-
-#define IsInQueue(bf) \
-( \
-	AssertMacro((bf->freeNext != INVALID_DESCRIPTOR)), \
-	AssertMacro((bf->freePrev != INVALID_DESCRIPTOR)), \
-	AssertMacro((bf->flags & BM_FREE)) \
-)
-
-#define IsNotInQueue(bf) \
-( \
-	AssertMacro((bf->freeNext == INVALID_DESCRIPTOR)), \
-	AssertMacro((bf->freePrev == INVALID_DESCRIPTOR)), \
-	AssertMacro(! (bf->flags & BM_FREE)) \
-)
-
-
-/*
- * AddBufferToFreelist
- *
- * In theory, this is the only routine that needs to be changed
- * if the buffer replacement strategy changes.	Just change
- * the manner in which buffers are added to the freelist queue.
- * Currently, they are added on an LRU basis.
- */
-static void
-AddBufferToFreelist(BufferDesc *bf)
+typedef struct bufstratcdb
 {
-#ifdef BMTRACE
-	_bm_trace(bf->tag.relId.dbId, bf->tag.relId.relId, bf->tag.blockNum,
-			  BufferDescriptorGetBuffer(bf), BMT_DEALLOC);
-#endif   /* BMTRACE */
-	IsNotInQueue(bf);
+	int				prev;		/* links in the queue */
+	int				next;
+	int				list;		/* current list */
+	BufferTag		buf_tag;	/* buffer key */
+	Buffer			buf_id;		/* currently assigned data buffer */
+	TransactionId	t1_xid;		/* the xid this entry went onto T1 */
+} BufferStrategyCDB;
 
-	/* change bf so it points to inFrontOfNew and its successor */
-	bf->freePrev = SharedFreeList->freePrev;
-	bf->freeNext = Free_List_Descriptor;
+/*
+ * The shared ARC control information.
+ */
+typedef struct bufstratcontrol
+{
 
-	/* insert new into chain */
-	BufferDescriptors[bf->freeNext].freePrev = bf->buf_id;
-	BufferDescriptors[bf->freePrev].freeNext = bf->buf_id;
+	int		target_T1_size;				/* What T1 size are we aiming for */
+	int		listUnusedCDB;				/* All unused StrategyCDB */
+	int		listHead[STRAT_NUM_LISTS];	/* ARC lists B1, T1, T2 and B2 */
+	int		listTail[STRAT_NUM_LISTS];
+	int		listSize[STRAT_NUM_LISTS];
+	Buffer	listFreeBuffers;			/* List of unused buffers */
+
+	long	num_lookup;					/* Some hit statistics */
+	long	num_hit[STRAT_NUM_LISTS];
+	time_t	stat_report;
+
+	BufferStrategyCDB	cdb[1];			/* The cache directory */
+} BufferStrategyControl;
+ 
+
+static BufferStrategyControl	*StrategyControl = NULL;
+static BufferStrategyCDB		*StrategyCDB = NULL;
+
+static int		strategy_cdb_found;
+static int		strategy_cdb_replace;
+static int		strategy_get_from;
+
+int				BufferStrategyStatInterval = 0;
+
+static bool				strategy_hint_vacuum;
+static TransactionId	strategy_vacuum_xid;
+
+
+#define T1_TARGET	StrategyControl->target_T1_size
+#define B1_LENGTH	StrategyControl->listSize[STRAT_LIST_B1]
+#define T1_LENGTH	StrategyControl->listSize[STRAT_LIST_T1]
+#define T2_LENGTH	StrategyControl->listSize[STRAT_LIST_T2]
+#define B2_LENGTH	StrategyControl->listSize[STRAT_LIST_B2]
+
+
+/*
+ * Macro to remove a CDB from whichever list it currently is on
+ */
+#define	STRAT_LIST_REMOVE(cdb) \
+{ \
+	AssertMacro((cdb)->list >= 0 && (cdb)->list < STRAT_NUM_LISTS);		\
+	if ((cdb)->prev < 0)												\
+		StrategyControl->listHead[(cdb)->list] = (cdb)->next;			\
+	else																\
+		StrategyCDB[(cdb)->prev].next = (cdb)->next;					\
+	if ((cdb)->next < 0)												\
+		StrategyControl->listTail[(cdb)->list] = (cdb)->prev;			\
+	else																\
+		StrategyCDB[(cdb)->next].prev = (cdb)->prev;					\
+	StrategyControl->listSize[(cdb)->list]--;							\
+	(cdb)->list = STRAT_LIST_UNUSED;									\
 }
 
+/*
+ * Macro to add a CDB to the tail of a list (MRU position)
+ */
+#define STRAT_MRU_INSERT(cdb,l) \
+{ \
+	AssertMacro((cdb)->list == STRAT_LIST_UNUSED);						\
+	if (StrategyControl->listTail[(l)] < 0)								\
+	{																	\
+		(cdb)->prev = (cdb)->next = -1;									\
+		StrategyControl->listHead[(l)] = 								\
+			StrategyControl->listTail[(l)] =							\
+			((cdb) - StrategyCDB);										\
+	}																	\
+	else																\
+	{																	\
+		(cdb)->next = -1;												\
+		(cdb)->prev = StrategyControl->listTail[(l)];					\
+		StrategyCDB[StrategyControl->listTail[(l)]].next = 				\
+			((cdb) - StrategyCDB);										\
+		StrategyControl->listTail[(l)] = 								\
+			((cdb) - StrategyCDB);										\
+	}																	\
+	StrategyControl->listSize[(l)]++;									\
+	(cdb)->list = (l);													\
+}
+
+/*
+ * Macro to add a CDB to the head of a list (LRU position)
+ */
+#define STRAT_LRU_INSERT(cdb,l) \
+{ \
+	AssertMacro((cdb)->list == STRAT_LIST_UNUSED);						\
+	if (StrategyControl->listHead[(l)] < 0)								\
+	{																	\
+		(cdb)->prev = (cdb)->next = -1;									\
+		StrategyControl->listHead[(l)] = 								\
+			StrategyControl->listTail[(l)] =							\
+			((cdb) - StrategyCDB);										\
+	}																	\
+	else																\
+	{																	\
+		(cdb)->prev = -1;												\
+		(cdb)->next = StrategyControl->listHead[(l)];					\
+		StrategyCDB[StrategyControl->listHead[(l)]].prev = 				\
+			((cdb) - StrategyCDB);										\
+		StrategyControl->listHead[(l)] = 								\
+			((cdb) - StrategyCDB);										\
+	}																	\
+	StrategyControl->listSize[(l)]++;									\
+	(cdb)->list = (l);													\
+}
+
+
+/*
+ * StrategyBufferLookup
+ *
+ *	Lookup a page request in the cache directory. A buffer is only
+ *	returned for a T1 or T2 cache hit. B1 and B2 hits are only
+ *	remembered here to later affect the behaviour.
+ */
+BufferDesc *
+StrategyBufferLookup(BufferTag *tagPtr, bool recheck)
+{
+	BufferStrategyCDB  *cdb;
+	time_t				now;
+
+	if (BufferStrategyStatInterval > 0)
+	{
+		time(&now);
+		if (StrategyControl->stat_report + BufferStrategyStatInterval < now)
+		{
+			long	all_hit, b1_hit, t1_hit, t2_hit, b2_hit;
+			ErrorContextCallback	*errcxtold;
+
+			if (StrategyControl->num_lookup == 0)
+			{
+				all_hit = b1_hit = t1_hit = t2_hit = b2_hit = 0;
+			}
+			else
+			{
+				b1_hit = (StrategyControl->num_hit[STRAT_LIST_B1] * 100 /
+						  StrategyControl->num_lookup);
+				t1_hit = (StrategyControl->num_hit[STRAT_LIST_T1] * 100 /
+						  StrategyControl->num_lookup);
+				t2_hit = (StrategyControl->num_hit[STRAT_LIST_T2] * 100 /
+						  StrategyControl->num_lookup);
+				b2_hit = (StrategyControl->num_hit[STRAT_LIST_B2] * 100 /
+						  StrategyControl->num_lookup);
+				all_hit = b1_hit + t1_hit + t2_hit + b2_hit;
+			}
+
+			errcxtold = error_context_stack;
+			error_context_stack = NULL;
+			elog(DEBUG1, "ARC T1target=%5d B1len=%5d T1len=%5d T2len=%5d B2len=%5d",
+					T1_TARGET, B1_LENGTH, T1_LENGTH, T2_LENGTH, B2_LENGTH);
+			elog(DEBUG1, "ARC total   =%4ld%% B1hit=%4ld%% T1hit=%4ld%% T2hit=%4ld%% B2hit=%4ld%%",
+					all_hit, b1_hit, t1_hit, t2_hit, b2_hit);
+			error_context_stack = errcxtold;
+
+			StrategyControl->num_lookup = 0;
+			StrategyControl->num_hit[STRAT_LIST_B1] = 0;
+			StrategyControl->num_hit[STRAT_LIST_T1] = 0;
+			StrategyControl->num_hit[STRAT_LIST_T2] = 0;
+			StrategyControl->num_hit[STRAT_LIST_B2] = 0;
+			StrategyControl->stat_report = now;
+		}
+	}
+
+	/*
+	 * Count lookups
+	 */
+	StrategyControl->num_lookup++;
+
+	/*
+	 * Lookup the block in the shared hash table
+	 */
+	strategy_cdb_found = BufTableLookup(tagPtr);
+
+	/*
+	 * Handle CDB lookup miss
+	 */
+	if (strategy_cdb_found < 0)
+	{
+		if (!recheck)
+		{
+			/*
+			 * This is an initial lookup and we have a complete
+			 * cache miss (block found nowhere). This means we
+			 * remember according to the current T1 size and the
+			 * target T1 size from where we take a block if we
+			 * need one later.
+			 */
+			if (T1_LENGTH >= MAX(1, T1_TARGET))
+				strategy_get_from = STRAT_LIST_T1;
+			else
+				strategy_get_from = STRAT_LIST_T2;
+		}
+
+		/* report cache miss */
+		return NULL;
+	}
+
+	/*
+	 * We found a CDB
+	 */
+	cdb = &StrategyCDB[strategy_cdb_found];
+
+	/*
+	 * Count hits
+	 */
+	StrategyControl->num_hit[cdb->list]++;
+
+	/*
+	 * If this is a T2 hit, we simply move the CDB to the
+	 * T2 MRU position and return the found buffer.
+	 */
+	if (cdb->list == STRAT_LIST_T2)
+	{
+		STRAT_LIST_REMOVE(cdb);
+		STRAT_MRU_INSERT(cdb, STRAT_LIST_T2);
+
+		return &BufferDescriptors[cdb->buf_id];
+	}
+
+	/*
+	 * If this is a T1 hit, we move the buffer to the T2 MRU
+	 * only if another transaction had read it into T1. This is
+	 * required because any UPDATE or DELETE in PostgreSQL does
+	 * multiple ReadBuffer(), first during the scan, later during
+	 * the heap_update() or heap_delete().
+	 */
+	if (cdb->list == STRAT_LIST_T1)
+	{
+		if (!TransactionIdIsCurrentTransactionId(cdb->t1_xid))
+		{
+			STRAT_LIST_REMOVE(cdb);
+			STRAT_MRU_INSERT(cdb, STRAT_LIST_T2);
+		}
+
+		return &BufferDescriptors[cdb->buf_id];
+	}
+
+	/*
+	 * In the case of a recheck we don't care about B1 or B2 hits here.
+	 * The bufmgr does this call only to make sure noone faulted in the
+	 * block while we where busy flushing another. Now for this really
+	 * to end up as a B1 or B2 cache hit, we must have been flushing for
+	 * quite some time as the block not only must have been read, but
+	 * also traveled through the queue and evicted from the T cache again
+	 * already. 
+	 */
+	if (recheck)
+		return NULL;
+
+	/*
+	 * Adjust the target size of the T1 cache depending on if this is
+	 * a B1 or B2 hit.
+	 */
+	switch (cdb->list)
+	{
+		case STRAT_LIST_B1:
+			/*
+			 * B1 hit means that the T1 cache is probably too
+			 * small. Adjust the T1 target size and continue
+			 * below.
+			 */
+			T1_TARGET = MIN(T1_TARGET + MAX(B2_LENGTH / B1_LENGTH, 1),
+							Data_Descriptors);
+			break;
+
+		case STRAT_LIST_B2:
+			/* 
+			 * B2 hit means that the T2 cache is probably too
+			 * small. Adjust the T1 target size and continue
+			 * below.
+ */
+			T1_TARGET = MAX(T1_TARGET - MAX(B1_LENGTH / B2_LENGTH, 1), 0);
+			break;
+
+		default:
+			elog(ERROR, "Buffer hash table corrupted - CDB on list %d found",
+					cdb->list);
+	}
+
+	/*
+	 * Decide where to take from if we will be out of
+	 * free blocks later in StrategyGetBuffer().
+	 */
+	if (T1_LENGTH >= MAX(1, T1_TARGET))
+		strategy_get_from = STRAT_LIST_T1;
+	else
+		strategy_get_from = STRAT_LIST_T2;
+
+	/*
+	 * Even if we had seen the block in the past, it's data is
+	 * not currently in memory ... cache miss to the bufmgr.
+	 */
+	return NULL;
+}
+
+
+/*
+ * StrategyGetBuffer
+ *
+ *	Called by the bufmgr to get the next candidate buffer to use in
+ *	BufferAlloc(). The only hard requirement BufferAlloc() has is that
+ *	this buffer must not currently be pinned. 
+ */
+BufferDesc *
+StrategyGetBuffer(void)
+{
+	int				cdb_id;
+	BufferDesc	   *buf;
+
+	if (StrategyControl->listFreeBuffers < 0)
+	{
+		/* We don't have a free buffer, must take one from T1 or T2 */
+
+		if (strategy_get_from == STRAT_LIST_T1)
+		{
+			/*
+			 * We should take the first unpinned buffer from T1.
+			 */
+			cdb_id = StrategyControl->listHead[STRAT_LIST_T1];
+			while (cdb_id >= 0)
+			{
+				buf = &BufferDescriptors[StrategyCDB[cdb_id].buf_id];
+				if (buf->refcount == 0)
+				{
+					strategy_cdb_replace = cdb_id;
+					Assert(StrategyCDB[cdb_id].list == STRAT_LIST_T1);
+					return buf;
+				}
+				cdb_id = StrategyCDB[cdb_id].next;
+			}
+
+			/*
+			 * No unpinned T1 buffer found - pardon T2 cache.
+			 */
+			cdb_id = StrategyControl->listHead[STRAT_LIST_T2];
+			while (cdb_id >= 0)
+			{
+				buf = &BufferDescriptors[StrategyCDB[cdb_id].buf_id];
+				if (buf->refcount == 0)
+				{
+					strategy_cdb_replace = cdb_id;
+					Assert(StrategyCDB[cdb_id].list == STRAT_LIST_T2);
+					return buf;
+				}
+				cdb_id = StrategyCDB[cdb_id].next;
+			}
+
+			/*
+			 * No unpinned buffers at all!!!
+			 */
+			elog(ERROR, "StrategyGetBuffer(): Out of unpinned buffers");
+		}
+		else
+		{
+			/*
+			 * We should take the first unpinned buffer from T2.
+			 */
+			cdb_id = StrategyControl->listHead[STRAT_LIST_T2];
+			while (cdb_id >= 0)
+			{
+				buf = &BufferDescriptors[StrategyCDB[cdb_id].buf_id];
+				if (buf->refcount == 0)
+				{
+					strategy_cdb_replace = cdb_id;
+					Assert(StrategyCDB[cdb_id].list == STRAT_LIST_T2);
+					return buf;
+				}
+				cdb_id = StrategyCDB[cdb_id].next;
+			}
+
+			/*
+			 * No unpinned T2 buffer found - pardon T1 cache.
+			 */
+			cdb_id = StrategyControl->listHead[STRAT_LIST_T1];
+			while (cdb_id >= 0)
+			{
+				buf = &BufferDescriptors[StrategyCDB[cdb_id].buf_id];
+				if (buf->refcount == 0)
+				{
+					strategy_cdb_replace = cdb_id;
+					Assert(StrategyCDB[cdb_id].list == STRAT_LIST_T1);
+					return buf;
+				}
+				cdb_id = StrategyCDB[cdb_id].next;
+			}
+
+			/*
+			 * No unpinned buffers at all!!!
+			 */
+			elog(ERROR, "StrategyGetBuffer(): Out of unpinned buffers");
+		}
+	}
+	else
+	{
+		/* There is a completely free buffer available - take it */
+
+		/*
+		 * Note: This code uses the side effect that a free buffer
+		 * can never be pinned or dirty and therefore the call to
+		 * StrategyReplaceBuffer() will happen without the bufmgr
+		 * releasing the bufmgr-lock in the meantime. That means,
+		 * that there will never be any reason to recheck. Otherwise
+		 * we would leak shared buffers here!
+		 */
+		strategy_cdb_replace = -1;
+		buf = &BufferDescriptors[StrategyControl->listFreeBuffers];
+
+		StrategyControl->listFreeBuffers = buf->bufNext;
+		buf->bufNext = -1;
+
+		/* Buffer of freelist cannot be pinned */
+		Assert(buf->refcount == 0);
+
+		return buf;
+	}
+
+	/* not reached */
+	return NULL;
+}
+
+
+/*
+ * StrategyReplaceBuffer
+ *
+ *	Called by the buffer manager to inform us that he possibly flushed
+ * 	a buffer and is now about to replace the content. Prior to this call,
+ *	the cache algorithm still reports the buffer as in the cache. After
+ *	this call we report the new block, even if IO might still need to
+ *	start.
+ */
+void
+StrategyReplaceBuffer(BufferDesc *buf, Relation rnode, BlockNumber blockNum)
+{
+	BufferStrategyCDB	   *cdb_found;
+	BufferStrategyCDB	   *cdb_replace;
+
+	if (strategy_cdb_found >= 0)
+	{
+		/* This was a ghost buffer cache hit (B1 or B2) */
+		cdb_found = &StrategyCDB[strategy_cdb_found];
+
+		/* Assert that the buffer remembered in cdb_found is the one */
+		/* the buffer manager is currently faulting in */
+		Assert(BUFFERTAG_EQUALS(&(cdb_found->buf_tag), rnode, blockNum));
+		
+		if (strategy_cdb_replace >= 0)
+		{
+			/* We are satisfying it with an evicted T buffer */
+			cdb_replace = &StrategyCDB[strategy_cdb_replace];
+
+			/* Assert that the buffer remembered in cdb_replace is */
+			/* the one the buffer manager has just evicted */
+			Assert(cdb_replace->list == STRAT_LIST_T1 || 
+					cdb_replace->list == STRAT_LIST_T2);
+			Assert(cdb_replace->buf_id == buf->buf_id);
+			Assert(BUFFERTAGS_EQUAL(&(cdb_replace->buf_tag), &(buf->tag)));
+
+			/* If this was a T1 buffer faulted in by vacuum, just */
+			/* do not cause the CDB end up in the B1 list, so that */
+			/* the vacuum scan does not affect T1_target adjusting */
+			if (strategy_hint_vacuum)
+			{
+				BufTableDelete(&(cdb_replace->buf_tag));
+				STRAT_LIST_REMOVE(cdb_replace);
+				cdb_replace->buf_id = -1;
+				cdb_replace->next = StrategyControl->listUnusedCDB;
+				StrategyControl->listUnusedCDB = strategy_cdb_replace;
+			}
+			else
+			{
+				/* Under normal circumstances move the evicted */
+				/* T list entry to it's corresponding B list */
+				if (cdb_replace->list == STRAT_LIST_T1)
+				{
+					STRAT_LIST_REMOVE(cdb_replace);
+					STRAT_MRU_INSERT(cdb_replace, STRAT_LIST_B1);
+				}
+				else
+				{
+					STRAT_LIST_REMOVE(cdb_replace);
+					STRAT_MRU_INSERT(cdb_replace, STRAT_LIST_B2);
+				}
+			}
+			/* And clear it's block reference */
+			cdb_replace->buf_id = -1;
+		}
+		else
+		{
+			/* or we satisfy it with an unused buffer */
+		}
+
+		/* Now the found B CDB get's the buffer and is moved to T2 */
+		cdb_found->buf_id = buf->buf_id;
+		STRAT_LIST_REMOVE(cdb_found);
+		STRAT_MRU_INSERT(cdb_found, STRAT_LIST_T2);
+	}
+	else
+	{
+		/* This was a complete cache miss, so we need to create */
+		/* a new CDB. The goal is to keep T1len+B1len <= c */
+
+		if (B1_LENGTH > 0 && (T1_LENGTH + B1_LENGTH) >= Data_Descriptors)
+		{
+			/* So if B1 isn't empty and T1len+B1len >= c we take B1-LRU */
+			cdb_found = &StrategyCDB[StrategyControl->listHead[STRAT_LIST_B1]];
+
+			BufTableDelete(&(cdb_found->buf_tag));
+			STRAT_LIST_REMOVE(cdb_found);
+		}
+		else
+		{
+			/* Otherwise, we try to use a free one */
+			if (StrategyControl->listUnusedCDB >= 0)
+			{
+				cdb_found = &StrategyCDB[StrategyControl->listUnusedCDB];
+				StrategyControl->listUnusedCDB = cdb_found->next;
+			}
+			else
+			{
+				/* If there isn't, we take B2-LRU ... except if */
+				/* T1len+B1len+T2len = c ... oh my */
+				if (B2_LENGTH > 0)
+					cdb_found = &StrategyCDB[StrategyControl->listHead[STRAT_LIST_B2]];
+				else
+					cdb_found = &StrategyCDB[StrategyControl->listHead[STRAT_LIST_B1]];
+
+				BufTableDelete(&(cdb_found->buf_tag));
+				STRAT_LIST_REMOVE(cdb_found);
+			}
+		}
+
+		/* Set the CDB's buf_tag and insert the hash key */
+		INIT_BUFFERTAG(&(cdb_found->buf_tag), rnode, blockNum);
+		BufTableInsert(&(cdb_found->buf_tag), (cdb_found - StrategyCDB));
+
+		if (strategy_cdb_replace >= 0)
+		{
+			/* The buffer was formerly in a T list, move it's CDB
+			 * to the corresponding B list */
+			cdb_replace = &StrategyCDB[strategy_cdb_replace];
+
+			Assert(cdb_replace->list == STRAT_LIST_T1 || 
+					cdb_replace->list == STRAT_LIST_T2);
+			Assert(cdb_replace->buf_id == buf->buf_id);
+			Assert(BUFFERTAGS_EQUAL(&(cdb_replace->buf_tag), &(buf->tag)));
+
+			if (cdb_replace->list == STRAT_LIST_T1)
+			{
+				STRAT_LIST_REMOVE(cdb_replace);
+				STRAT_MRU_INSERT(cdb_replace, STRAT_LIST_B1);
+			}
+			else
+			{
+				STRAT_LIST_REMOVE(cdb_replace);
+				STRAT_MRU_INSERT(cdb_replace, STRAT_LIST_B2);
+			}
+			/* And clear it's block reference */
+			cdb_replace->buf_id = -1;
+		}
+		else
+		{
+			/* or we satisfy it with an unused buffer */
+		}
+
+		/* Assign the buffer id to the new CDB */
+		cdb_found->buf_id = buf->buf_id;
+
+		/*
+		 * Specialized VACUUM optimization. If this "complete cache miss"
+		 * happened because vacuum needed the page, we want it later on
+		 * to be placed at the LRU instead of the MRU position of T1.
+		 */
+		if (strategy_hint_vacuum)
+		{
+			if (strategy_vacuum_xid != GetCurrentTransactionId())
+			{
+				strategy_hint_vacuum = false;
+				STRAT_MRU_INSERT(cdb_found, STRAT_LIST_T1);
+			}
+			else
+				STRAT_LRU_INSERT(cdb_found, STRAT_LIST_T1);
+			
+		}
+		else
+			STRAT_MRU_INSERT(cdb_found, STRAT_LIST_T1);
+
+		/*
+		 * Remember the Xid when this buffer went onto T1 to avoid
+		 * a single UPDATE promoting a newcomer straight into T2.
+		 */
+		cdb_found->t1_xid = GetCurrentTransactionId();
+	}
+}
+
+
+/*
+ * StrategyInvalidateBuffer
+ *
+ *	Called by the buffer manager to inform us that a buffer content
+ *	is no longer valid. We simply throw away any eventual existing
+ *	buffer hash entry and move the CDB and buffer to the free lists.
+ */
+void
+StrategyInvalidateBuffer(BufferDesc *buf)
+{
+	int					cdb_id;
+	BufferStrategyCDB  *cdb;
+
+	cdb_id = BufTableLookup(&(buf->tag));
+
+	/* If we have the buffer somewhere in the directory, remove it
+	 * and add the CDB to the list of unused CDB's. */
+	if (cdb_id >= 0)
+	{
+		cdb = &StrategyCDB[cdb_id];
+		BufTableDelete(&(cdb->buf_tag));
+		STRAT_LIST_REMOVE(cdb);
+		cdb->buf_id = -1;
+		cdb->next = StrategyControl->listUnusedCDB;
+		StrategyControl->listUnusedCDB = cdb_id;
+	}
+
+	/* Buffer is unreferenced now and should not contain any valid data
+	 * so add it to the list of free buffers */
+	buf->bufNext = StrategyControl->listFreeBuffers;
+	StrategyControl->listFreeBuffers = buf->buf_id;
+}
+
+
+void
+StrategyHintVacuum(bool vacuum_active)
+{
+	strategy_hint_vacuum = vacuum_active;
+	strategy_vacuum_xid = GetCurrentTransactionId();
+}
+
+
+int
+StrategyDirtyBufferList(int *buffer_list, int max_buffers)
+{
+	int					num_buffer_dirty = 0;
+	int					cdb_id_t1;
+	int					cdb_id_t2;
+	int					buf_id;
+	BufferDesc		   *buf;
+
+	/*
+	 * Traverse the T1 and T2 list LRU to MRU in "parallel"
+	 * and add all dirty buffers found in that order to the list.
+	 * The ARC strategy keeps all used buffers including pinned ones
+	 * in the T1 or T2 list. So we cannot loose any dirty buffers.
+	 */
+	cdb_id_t1 = StrategyControl->listHead[STRAT_LIST_T1];
+	cdb_id_t2 = StrategyControl->listHead[STRAT_LIST_T2];
+
+	while ((cdb_id_t1 >= 0 || cdb_id_t2 >= 0) && 
+			num_buffer_dirty < max_buffers)
+	{
+		if (cdb_id_t1 >= 0)
+		{
+			buf_id = StrategyCDB[cdb_id_t1].buf_id;
+			buf = &BufferDescriptors[buf_id];
+
+			if (buf->flags & BM_VALID)
+			{
+				if ((buf->flags & BM_DIRTY) || (buf->cntxDirty))
+				{
+					buffer_list[num_buffer_dirty++] = buf_id;
+				}
+			}
+
+			cdb_id_t1 = StrategyCDB[cdb_id_t1].next;
+		}
+
+		if (cdb_id_t2 >= 0)
+		{
+			buf_id = StrategyCDB[cdb_id_t2].buf_id;
+			buf = &BufferDescriptors[buf_id];
+
+			if (buf->flags & BM_VALID)
+			{
+				if ((buf->flags & BM_DIRTY) || (buf->cntxDirty))
+				{
+					buffer_list[num_buffer_dirty++] = buf_id;
+				}
+			}
+
+			cdb_id_t2 = StrategyCDB[cdb_id_t2].next;
+		}
+	}
+
+	return num_buffer_dirty;
+}
+
+
+/*
+ * StrategyInitialize -- initialize the buffer cache replacement
+ *		strategy.
+ *
+ * Assume: All of the buffers are already building a linked list.
+ *		Only called by postmaster and only during initialization.
+ */
+void
+StrategyInitialize(bool init)
+{
+	bool found;
+	int i;
+
+	/*
+	 * Initialize the shared CDB lookup hashtable
+	 */
+	InitBufTable(Data_Descriptors * 2);
+
+	/*
+	 * Get or create the shared strategy control block and the CDB's
+	 */
+	StrategyControl = (BufferStrategyControl *)
+			ShmemInitStruct("Buffer Strategy Status",
+					sizeof(BufferStrategyControl) +
+					sizeof(BufferStrategyCDB) * (Data_Descriptors * 2 - 1),
+					&found);
+	StrategyCDB = &(StrategyControl->cdb[0]);
+
+	if (!found)
+	{
+		/*
+		 * Only done once, usually in postmaster
+		 */
+		Assert(init);
+
+		/*
+		 * Grab the whole linked list of free buffers for our
+		 * strategy
+		 */
+		StrategyControl->listFreeBuffers = 0;
+
+		/*
+		 * We start off with a target T1 list size of
+		 * half the available cache blocks.
+		 */
+		StrategyControl->target_T1_size = Data_Descriptors / 2;
+
+		/*
+		 * Initialize B1, T1, T2 and B2 lists to be empty
+		 */
+		for (i = 0; i < STRAT_NUM_LISTS; i++)
+		{
+			StrategyControl->listHead[i] = -1;
+			StrategyControl->listTail[i] = -1;
+			StrategyControl->listSize[i] = 0;
+			StrategyControl->num_hit[i] = 0;
+		}
+		StrategyControl->num_lookup  = 0;
+		StrategyControl->stat_report = 0;
+
+		/*
+		 * All CDB's are linked as the listUnusedCDB
+		 */
+		for (i = 0; i < Data_Descriptors * 2; i++)
+		{
+			StrategyCDB[i].next = i + 1;
+			StrategyCDB[i].list = STRAT_LIST_UNUSED;
+			CLEAR_BUFFERTAG(&(StrategyCDB[i].buf_tag));
+			StrategyCDB[i].buf_id = -1;
+		}
+		StrategyCDB[Data_Descriptors * 2 - 1].next = -1;
+		StrategyControl->listUnusedCDB = 0;
+	}
+	else
+	{
+		Assert(!init);
+	}
+}
+
+
 #undef PinBuffer
 
 /*
@@ -95,18 +853,9 @@ PinBuffer(BufferDesc *buf)
 
 	if (buf->refcount == 0)
 	{
-		IsInQueue(buf);
-
-		/* remove from freelist queue */
-		BufferDescriptors[buf->freeNext].freePrev = buf->freePrev;
-		BufferDescriptors[buf->freePrev].freeNext = buf->freeNext;
-		buf->freeNext = buf->freePrev = INVALID_DESCRIPTOR;
-
 		/* mark buffer as no longer free */
 		buf->flags &= ~BM_FREE;
 	}
-	else
-		IsNotInQueue(buf);
 
 	if (PrivateRefCount[b] == 0)
 		buf->refcount++;
@@ -144,7 +893,6 @@ UnpinBuffer(BufferDesc *buf)
 {
 	int			b = BufferDescriptorGetBuffer(buf) - 1;
 
-	IsNotInQueue(buf);
 	Assert(buf->refcount > 0);
 	Assert(PrivateRefCount[b] > 0);
 	PrivateRefCount[b]--;
@@ -154,7 +902,6 @@ UnpinBuffer(BufferDesc *buf)
 	if (buf->refcount == 0)
 	{
 		/* buffer is now unpinned */
-		AddBufferToFreelist(buf);
 		buf->flags |= BM_FREE;
 	}
 	else if ((buf->flags & BM_PIN_COUNT_WAITER) != 0 &&
@@ -187,64 +934,6 @@ refcount = %ld, file: %s, line: %d\n",
 }
 #endif
 
-/*
- * GetFreeBuffer() -- get the 'next' buffer from the freelist.
- */
-BufferDesc *
-GetFreeBuffer(void)
-{
-	BufferDesc *buf;
-
-	if (Free_List_Descriptor == SharedFreeList->freeNext)
-	{
-		/* queue is empty. All buffers in the buffer pool are pinned. */
-		ereport(ERROR,
-				(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
-				 errmsg("out of free buffers")));
-		return NULL;
-	}
-	buf = &(BufferDescriptors[SharedFreeList->freeNext]);
-
-	/* remove from freelist queue */
-	BufferDescriptors[buf->freeNext].freePrev = buf->freePrev;
-	BufferDescriptors[buf->freePrev].freeNext = buf->freeNext;
-	buf->freeNext = buf->freePrev = INVALID_DESCRIPTOR;
-
-	buf->flags &= ~(BM_FREE);
-
-	return buf;
-}
-
-/*
- * InitFreeList -- initialize the dummy buffer descriptor used
- *		as a freelist head.
- *
- * Assume: All of the buffers are already linked in a circular
- *		queue.	 Only called by postmaster and only during
- *		initialization.
- */
-void
-InitFreeList(bool init)
-{
-	SharedFreeList = &(BufferDescriptors[Free_List_Descriptor]);
-
-	if (init)
-	{
-		/* we only do this once, normally in the postmaster */
-		SharedFreeList->data = INVALID_OFFSET;
-		SharedFreeList->flags = 0;
-		SharedFreeList->flags &= ~(BM_VALID | BM_DELETED | BM_FREE);
-		SharedFreeList->buf_id = Free_List_Descriptor;
-
-		/* insert it into a random spot in the circular queue */
-		SharedFreeList->freeNext = BufferDescriptors[0].freeNext;
-		SharedFreeList->freePrev = 0;
-		BufferDescriptors[SharedFreeList->freeNext].freePrev =
-			BufferDescriptors[SharedFreeList->freePrev].freeNext =
-			Free_List_Descriptor;
-	}
-}
-
 
 /*
  * print out the free list and check for breaks.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 44e492b6a9..ac235ecc3a 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.166 2003/11/07 21:27:38 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.167 2003/11/13 00:40:01 wieck Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -73,6 +73,7 @@ extern int	CheckPointTimeout;
 extern int	CommitDelay;
 extern int	CommitSiblings;
 extern char *preload_libraries_string;
+extern int	BufferStrategyStatInterval;
 
 #ifdef HAVE_SYSLOG
 extern char *Syslog_facility;
@@ -1190,6 +1191,15 @@ static struct config_int ConfigureNamesInt[] =
 		-1, -1, INT_MAX / 1000, NULL, NULL
 	},
 
+	{
+		{"buffer_strategy_status_interval", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Interval to report buffer strategy status in seconds"),
+			NULL
+		},
+		&BufferStrategyStatInterval,
+		0, 0, 600, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 1ead89e130..15c73e6692 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -58,6 +58,7 @@
 #shared_buffers = 1000		# min 16, at least max_connections*2, 8KB each
 #sort_mem = 1024		# min 64, size in KB
 #vacuum_mem = 8192		# min 1024, size in KB
+#buffer_strategy_status_interval = 0	# 0-600 seconds
 
 # - Free Space Map -
 
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 1c1c1d3451..492f16cc11 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: miscadmin.h,v 1.134 2003/09/24 18:54:01 tgl Exp $
+ * $Id: miscadmin.h,v 1.135 2003/11/13 00:40:01 wieck Exp $
  *
  * NOTES
  *	  some of the information in this file should be moved to
@@ -96,6 +96,13 @@ extern void ProcessInterrupts(void);
 		CritSectionCount--; \
 	} while(0)
 
+#define PG_DELAY(_msec) \
+{ \
+	struct timeval delay; \
+	delay.tv_sec = (_msec) / 1000; \
+	delay.tv_usec = ((_msec) % 1000) * 1000; \
+	(void) select(0, NULL, NULL, NULL, &delay); \
+}
 
 /*****************************************************************************
  *	  globals.h --															 *
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index f2d615151e..deafa0b8ce 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: buf_internals.h,v 1.61 2003/08/04 02:40:14 momjian Exp $
+ * $Id: buf_internals.h,v 1.62 2003/11/13 00:40:02 wieck Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -72,17 +72,29 @@ typedef struct buftag
 	(a)->rnode = (xx_reln)->rd_node \
 )
 
+#define BUFFERTAG_EQUALS(a,xx_reln,xx_blockNum) \
+( \
+	(a)->rnode.tblNode == (xx_reln)->rd_node.tblNode && \
+	(a)->rnode.relNode == (xx_reln)->rd_node.relNode && \
+	(a)->blockNum == (xx_blockNum) \
+)
+#define BUFFERTAGS_EQUAL(a,b) \
+( \
+	(a)->rnode.tblNode == (b)->rnode.tblNode && \
+	(a)->rnode.relNode == (b)->rnode.relNode && \
+	(a)->blockNum == (b)->blockNum \
+)
+
 /*
  *	BufferDesc -- shared buffer cache metadata for a single
  *				  shared buffer descriptor.
  */
 typedef struct sbufdesc
 {
-	Buffer		freeNext;		/* links for freelist chain */
-	Buffer		freePrev;
+	Buffer		bufNext;		/* link in freelist chain */
 	SHMEM_OFFSET data;			/* pointer to data in buf pool */
 
-	/* tag and id must be together for table lookup (still true?) */
+	/* tag and id must be together for table lookup */
 	BufferTag	tag;			/* file/block identifier */
 	int			buf_id;			/* buffer's index number (from 0) */
 
@@ -107,6 +119,7 @@ typedef struct sbufdesc
 
 #define BufferDescriptorGetBuffer(bdesc) ((bdesc)->buf_id + 1)
 
+
 /*
  * Each backend has its own BufferLocks[] array holding flag bits
  * showing what locks it has set on each buffer.
@@ -167,14 +180,19 @@ extern long int LocalBufferFlushCount;
 /*freelist.c*/
 extern void PinBuffer(BufferDesc *buf);
 extern void UnpinBuffer(BufferDesc *buf);
-extern BufferDesc *GetFreeBuffer(void);
-extern void InitFreeList(bool init);
+extern BufferDesc *StrategyBufferLookup(BufferTag *tagPtr, bool recheck);
+extern BufferDesc *StrategyGetBuffer(void);
+extern void StrategyReplaceBuffer(BufferDesc *buf, Relation rnode, BlockNumber blockNum);
+extern void StrategyInvalidateBuffer(BufferDesc *buf);
+extern void StrategyHintVacuum(bool vacuum_active);
+extern int StrategyDirtyBufferList(int *buffer_dirty, int max_buffers);
+extern void StrategyInitialize(bool init);
 
 /* buf_table.c */
-extern void InitBufTable(void);
-extern BufferDesc *BufTableLookup(BufferTag *tagPtr);
-extern bool BufTableDelete(BufferDesc *buf);
-extern bool BufTableInsert(BufferDesc *buf);
+extern void InitBufTable(int size);
+extern int BufTableLookup(BufferTag *tagPtr);
+extern bool BufTableInsert(BufferTag *tagPtr, Buffer buf_id);
+extern bool BufTableDelete(BufferTag *tagPtr);
 
 /* bufmgr.c */
 extern BufferDesc *BufferDescriptors;