This patch extracts page buffer pooling and the simple

least-recently-used strategy from clog.c into slru.c.  It doesn't
change any visible behaviour and passes all regression tests plus a
TruncateCLOG test done manually.

Apart from refactoring I made a little change to SlruRecentlyUsed,
formerly ClogRecentlyUsed:  It now skips incrementing lru_counts, if
slotno is already the LRU slot, thus saving a few CPU cycles.  To make
this work, lru_counts are initialised to 1 in SimpleLruInit.

SimpleLru will be used by pg_subtrans (part of the nested transactions
project), so the main purpose of this patch is to avoid future code
duplication.

Manfred Koizar

src/backend/access/transam/Makefile

@@ -4,7 +4,7 @@
 #    Makefile for access/transam
 #
 # IDENTIFICATION
-#    $Header: /cvsroot/pgsql/src/backend/access/transam/Makefile,v 1.16 2003/05/12 23:08:50 tgl Exp $
+#    $Header: /cvsroot/pgsql/src/backend/access/transam/Makefile,v 1.17 2003/06/11 22:37:45 momjian Exp $
 #
 #-------------------------------------------------------------------------
 
@@ -12,7 +12,7 @@ subdir = src/backend/access/transam
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = clog.o transam.o varsup.o xact.o xlog.o xlogutils.o rmgr.o
+OBJS = clog.o transam.o varsup.o xact.o xlog.o xlogutils.o rmgr.o slru.o
 
 all: SUBSYS.o
 

src/backend/storage/lmgr/lwlock.c

@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/lmgr/lwlock.c,v 1.14 2002/09/25 20:31:40 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/lmgr/lwlock.c,v 1.15 2003/06/11 22:37:45 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -108,8 +108,8 @@ NumLWLocks(void)
 	/* bufmgr.c needs two for each shared buffer */
 	numLocks += 2 * NBuffers;
 
-	/* clog.c needs one per CLOG buffer */
-	numLocks += NUM_CLOG_BUFFERS;
+	/* clog.c needs one per CLOG buffer + one control lock */
+	numLocks += NUM_CLOG_BUFFERS + 1;
 
 	/* Perhaps create a few more for use by user-defined modules? */
 

src/include/access/slru.h

+/*
+ * slru.h
+ *
+ * Simple LRU
+ *
+ * Portions Copyright (c) 2003, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * $Id: slru.h,v 1.1 2003/06/11 22:37:46 momjian Exp $
+ */
+#ifndef SLRU_H
+#define SLRU_H
+
+#include "access/xlog.h"
+
+/* exported because lwlock.c needs it */
+#define NUM_CLOG_BUFFERS	8
+
+typedef struct SlruLockData
+{
+	LWLockId ControlLock;
+/*
+ * BufferLocks is set during CLOGShmemInit and does not change thereafter.
+ * The value is automatically inherited by backends via fork, and
+ * doesn't need to be in shared memory.
+ */
+	LWLockId BufferLocks[NUM_CLOG_BUFFERS];		/* Per-buffer I/O locks */
+} SlruLockData;
+typedef SlruLockData *SlruLock;
+
+typedef struct SlruCtlData
+{
+	void *shared;	/* pointer to SlruSharedData */
+	SlruLock locks;
+
+/*
+ * Dir is set during SimpleLruShmemInit and does not change thereafter.
+ * The value is automatically inherited by backends via fork, and
+ * doesn't need to be in shared memory.
+ */
+	char Dir[MAXPGPATH];
+	
+/*
+ * Decide which of two page numbers is "older" for truncation purposes.
+ * We need to use comparison of TransactionIds here in order to do the right
+ * thing with wraparound XID arithmetic.
+ */
+	bool (*PagePrecedes)(int, int);
+
+} SlruCtlData;
+typedef SlruCtlData *SlruCtl;
+
+extern int	SimpleLruShmemSize(void);
+extern void SimpleLruInit(SlruCtl ctl, const char *name, const char *subdir);
+extern int	SimpleLruZeroPage(SlruCtl ctl, int pageno);
+extern char	*SimpleLruReadPage(SlruCtl ctl, int pageno, TransactionId xid, bool forwrite);
+extern void SimpleLruWritePage(SlruCtl ctl, int slotno);
+extern void SimpleLruSetLatestPage(SlruCtl ctl, int pageno);
+extern void SimpleLruFlush(SlruCtl ctl, bool checkpoint);
+extern void SimpleLruTruncate(SlruCtl ctl, int cutoffPage);
+
+#endif   /* SLRU_H */

src/include/storage/lwlock.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: lwlock.h,v 1.6 2002/06/20 20:29:52 momjian Exp $
+ * $Id: lwlock.h,v 1.7 2003/06/11 22:37:46 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -37,7 +37,6 @@ typedef enum LWLockId
 	WALWriteLock,
 	ControlFileLock,
 	CheckpointLock,
-	CLogControlLock,
 	RelCacheInitLock,
 
 	NumFixedLWLocks,			/* must be last except for