Rearrange pg_subtrans handling as per recent discussion. pg_subtrans

updates are no longer WAL-logged nor even fsync'd; we do not need to,
since after a crash no old pg_subtrans data is needed again.  We truncate
pg_subtrans to RecentGlobalXmin at each checkpoint.  slru.c's API is
refactored a little bit to separate out the necessary decisions.

Author: tglsfdc

src/backend/access/transam/clog.c

@@ -10,29 +10,34 @@
  * looked up again.  Now we use specialized access code so that the commit
  * log can be broken into relatively small, independent segments.
  *
+ * XLOG interactions: this module generates an XLOG record whenever a new
+ * CLOG page is initialized to zeroes.	Other writes of CLOG come from
+ * recording of transaction commit or abort in xact.c, which generates its
+ * own XLOG records for these events and will re-perform the status update
+ * on redo; so we need make no additional XLOG entry here.	Also, the XLOG
+ * is guaranteed flushed through the XLOG commit record before we are called
+ * to log a commit, so the WAL rule "write xlog before data" is satisfied
+ * automatically for commits, and we don't really care for aborts.  Therefore,
+ * we don't need to mark CLOG pages with LSN information; we have enough
+ * synchronization already.
+ *
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.22 2004/07/03 02:55:56 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.23 2004/08/23 23:22:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
-#include <fcntl.h>
-#include <dirent.h>
-#include <sys/stat.h>
-#include <unistd.h>
-
 #include "access/clog.h"
 #include "access/slru.h"
-#include "miscadmin.h"
-#include "storage/lwlock.h"
+#include "postmaster/bgwriter.h"
 
 
 /*
- * Defines for CLOG page and segment sizes.  A page is the same BLCKSZ
- * as is used everywhere else in Postgres.
+ * Defines for CLOG page sizes.  A page is the same BLCKSZ as is used
+ * everywhere else in Postgres.
  *
  * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF,
  * CLOG page numbering also wraps around at 0xFFFFFFFF/CLOG_XACTS_PER_PAGE,
@@ -53,25 +58,11 @@
 #define TransactionIdToBIndex(xid)	((xid) % (TransactionId) CLOG_XACTS_PER_BYTE)
 
 
-/*----------
- * Shared-memory data structures for CLOG control
- *
- * XLOG interactions: this module generates an XLOG record whenever a new
- * CLOG page is initialized to zeroes.	Other writes of CLOG come from
- * recording of transaction commit or abort in xact.c, which generates its
- * own XLOG records for these events and will re-perform the status update
- * on redo; so we need make no additional XLOG entry here.	Also, the XLOG
- * is guaranteed flushed through the XLOG commit record before we are called
- * to log a commit, so the WAL rule "write xlog before data" is satisfied
- * automatically for commits, and we don't really care for aborts.  Therefore,
- * we don't need to mark CLOG pages with LSN information; we have enough
- * synchronization already.
- *----------
+/*
+ * Link to shared-memory data structures for CLOG control
  */
-
-
 static SlruCtlData ClogCtlData;
-static SlruCtl ClogCtl = &ClogCtlData;
+#define ClogCtl (&ClogCtlData)
 
 
 static int	ZeroCLOGPage(int pageno, bool writeXlog);
@@ -91,17 +82,18 @@ TransactionIdSetStatus(TransactionId xid, XidStatus status)
 	int			pageno = TransactionIdToPage(xid);
 	int			byteno = TransactionIdToByte(xid);
 	int			bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
+	int			slotno;
 	char	   *byteptr;
 	char		byteval;
 
 	Assert(status == TRANSACTION_STATUS_COMMITTED ||
 		   status == TRANSACTION_STATUS_ABORTED ||
 		   status == TRANSACTION_STATUS_SUB_COMMITTED);
 
-	LWLockAcquire(ClogCtl->ControlLock, LW_EXCLUSIVE);
+	LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
 
-	byteptr = SimpleLruReadPage(ClogCtl, pageno, xid, true);
-	byteptr += byteno;
+	slotno = SimpleLruReadPage(ClogCtl, pageno, xid);
+	byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
 
 	/* Current state should be 0, subcommitted or target state */
 	Assert(((*byteptr >> bshift) & CLOG_XACT_BITMASK) == 0 ||
@@ -114,9 +106,9 @@ TransactionIdSetStatus(TransactionId xid, XidStatus status)
 	byteval |= (status << bshift);
 	*byteptr = byteval;
 
-	/* ...->page_status[slotno] = SLRU_PAGE_DIRTY; already done */
+	ClogCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
 
-	LWLockRelease(ClogCtl->ControlLock);
+	LWLockRelease(CLogControlLock);
 }
 
 /*
@@ -131,17 +123,18 @@ TransactionIdGetStatus(TransactionId xid)
 	int			pageno = TransactionIdToPage(xid);
 	int			byteno = TransactionIdToByte(xid);
 	int			bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
+	int			slotno;
 	char	   *byteptr;
 	XidStatus	status;
 
-	LWLockAcquire(ClogCtl->ControlLock, LW_EXCLUSIVE);
+	LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
 
-	byteptr = SimpleLruReadPage(ClogCtl, pageno, xid, false);
-	byteptr += byteno;
+	slotno = SimpleLruReadPage(ClogCtl, pageno, xid);
+	byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
 
 	status = (*byteptr >> bshift) & CLOG_XACT_BITMASK;
 
-	LWLockRelease(ClogCtl->ControlLock);
+	LWLockRelease(CLogControlLock);
 
 	return status;
 }
@@ -160,8 +153,8 @@ CLOGShmemSize(void)
 void
 CLOGShmemInit(void)
 {
-	SimpleLruInit(ClogCtl, "CLOG Ctl", "pg_clog");
 	ClogCtl->PagePrecedes = CLOGPagePrecedes;
+	SimpleLruInit(ClogCtl, "CLOG Ctl", CLogControlLock, "pg_clog");
 }
 
 /*
@@ -175,16 +168,16 @@ BootStrapCLOG(void)
 {
 	int			slotno;
 
-	LWLockAcquire(ClogCtl->ControlLock, LW_EXCLUSIVE);
+	LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
 
 	/* Create and zero the first page of the commit log */
 	slotno = ZeroCLOGPage(0, false);
 
 	/* Make sure it's written out */
 	SimpleLruWritePage(ClogCtl, slotno, NULL);
-	/* Assert(ClogCtl->page_status[slotno] == SLRU_PAGE_CLEAN); */
+	Assert(ClogCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
 
-	LWLockRelease(ClogCtl->ControlLock);
+	LWLockRelease(CLogControlLock);
 }
 
 /*
@@ -199,7 +192,9 @@ BootStrapCLOG(void)
 static int
 ZeroCLOGPage(int pageno, bool writeXlog)
 {
-	int			slotno = SimpleLruZeroPage(ClogCtl, pageno);
+	int			slotno;
+
+	slotno = SimpleLruZeroPage(ClogCtl, pageno);
 
 	if (writeXlog)
 		WriteZeroPageXlogRec(pageno);
@@ -217,8 +212,7 @@ StartupCLOG(void)
 	/*
 	 * Initialize our idea of the latest page number.
 	 */
-	SimpleLruSetLatestPage(ClogCtl,
-						   TransactionIdToPage(ShmemVariableCache->nextXid));
+	ClogCtl->shared->latest_page_number = TransactionIdToPage(ShmemVariableCache->nextXid);
 }
 
 /*
@@ -227,6 +221,7 @@ StartupCLOG(void)
 void
 ShutdownCLOG(void)
 {
+	/* Flush dirty CLOG pages to disk */
 	SimpleLruFlush(ClogCtl, false);
 }
 
@@ -236,6 +231,7 @@ ShutdownCLOG(void)
 void
 CheckPointCLOG(void)
 {
+	/* Flush dirty CLOG pages to disk */
 	SimpleLruFlush(ClogCtl, true);
 }
 
@@ -263,12 +259,12 @@ ExtendCLOG(TransactionId newestXact)
 
 	pageno = TransactionIdToPage(newestXact);
 
-	LWLockAcquire(ClogCtl->ControlLock, LW_EXCLUSIVE);
+	LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
 
 	/* Zero the page and make an XLOG entry about it */
 	ZeroCLOGPage(pageno, true);
 
-	LWLockRelease(ClogCtl->ControlLock);
+	LWLockRelease(CLogControlLock);
 }
 
 
@@ -296,6 +292,15 @@ TruncateCLOG(TransactionId oldestXact)
 	 * We pass the *page* containing oldestXact to SimpleLruTruncate.
 	 */
 	cutoffPage = TransactionIdToPage(oldestXact);
+
+	/* Check to see if there's any files that could be removed */
+	if (!SlruScanDirectory(ClogCtl, cutoffPage, false))
+		return;					/* nothing to remove */
+
+	/* Perform a CHECKPOINT */
+	RequestCheckpoint(true);
+
+	/* Now we can remove the old CLOG segment(s) */
 	SimpleLruTruncate(ClogCtl, cutoffPage);
 }
 
@@ -340,20 +345,51 @@ WriteZeroPageXlogRec(int pageno)
 	rdata.data = (char *) (&pageno);
 	rdata.len = sizeof(int);
 	rdata.next = NULL;
-	(void) XLogInsert(RM_SLRU_ID, CLOG_ZEROPAGE | XLOG_NO_TRAN, &rdata);
+	(void) XLogInsert(RM_CLOG_ID, CLOG_ZEROPAGE | XLOG_NO_TRAN, &rdata);
 }
 
-/* Redo a ZEROPAGE action during WAL replay */
+/*
+ * CLOG resource manager's routines
+ */
 void
-clog_zeropage_redo(int pageno)
+clog_redo(XLogRecPtr lsn, XLogRecord *record)
 {
-	int			slotno;
+	uint8		info = record->xl_info & ~XLR_INFO_MASK;
 
-	LWLockAcquire(ClogCtl->ControlLock, LW_EXCLUSIVE);
+	if (info == CLOG_ZEROPAGE)
+	{
+		int			pageno;
+		int			slotno;
 
-	slotno = ZeroCLOGPage(pageno, false);
-	SimpleLruWritePage(ClogCtl, slotno, NULL);
-	/* Assert(ClogCtl->page_status[slotno] == SLRU_PAGE_CLEAN); */
+		memcpy(&pageno, XLogRecGetData(record), sizeof(int));
+
+		LWLockAcquire(CLogControlLock, LW_EXCLUSIVE);
+
+		slotno = ZeroCLOGPage(pageno, false);
+		SimpleLruWritePage(ClogCtl, slotno, NULL);
+		Assert(ClogCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+
+		LWLockRelease(CLogControlLock);
+	}
+}
+
+void
+clog_undo(XLogRecPtr lsn, XLogRecord *record)
+{
+}
+
+void
+clog_desc(char *buf, uint8 xl_info, char *rec)
+{
+	uint8		info = xl_info & ~XLR_INFO_MASK;
+
+	if (info == CLOG_ZEROPAGE)
+	{
+		int			pageno;
 
-	LWLockRelease(ClogCtl->ControlLock);
+		memcpy(&pageno, rec, sizeof(int));
+		sprintf(buf + strlen(buf), "zeropage: %d", pageno);
+	}
+	else
+		strcat(buf, "UNKNOWN");
 }

src/backend/access/transam/rmgr.c

@@ -3,7 +3,7 @@
  *
  * Resource managers definition
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/rmgr.c,v 1.14 2004/07/21 22:31:20 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/rmgr.c,v 1.15 2004/08/23 23:22:44 tgl Exp $
  */
 #include "postgres.h"
 
@@ -12,7 +12,7 @@
 #include "access/heapam.h"
 #include "access/nbtree.h"
 #include "access/rtree.h"
-#include "access/slru.h"
+#include "access/clog.h"
 #include "access/xact.h"
 #include "access/xlog_internal.h"
 #include "storage/smgr.h"
@@ -23,7 +23,7 @@ const RmgrData RmgrTable[RM_MAX_ID + 1] = {
 	{"XLOG", xlog_redo, xlog_undo, xlog_desc, NULL, NULL},
 	{"Transaction", xact_redo, xact_undo, xact_desc, NULL, NULL},
 	{"Storage", smgr_redo, smgr_undo, smgr_desc, NULL, NULL},
-	{"SLRU", slru_redo, slru_undo, slru_desc, NULL, NULL},
+	{"CLOG", clog_redo, clog_undo, clog_desc, NULL, NULL},
 	{"Reserved 4", NULL, NULL, NULL, NULL, NULL},
 	{"Reserved 5", NULL, NULL, NULL, NULL, NULL},
 	{"Reserved 6", NULL, NULL, NULL, NULL, NULL},