Clean up representation of SLRU page state. This is the cleaner fix

for the SLRU race condition that I posted a few days ago, but we decided
not to use in 8.1 and older branches.

src/backend/access/transam/clog.c

@@ -24,7 +24,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.33 2005/10/15 02:49:09 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.34 2005/11/05 21:19:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -107,7 +107,7 @@ TransactionIdSetStatus(TransactionId xid, XidStatus status)
 	byteval |= (status << bshift);
 	*byteptr = byteval;
 
-	ClogCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
+	ClogCtl->shared->page_dirty[slotno] = true;
 
 	LWLockRelease(CLogControlLock);
 }
@@ -175,7 +175,7 @@ BootStrapCLOG(void)
 
 	/* Make sure it's written out */
 	SimpleLruWritePage(ClogCtl, slotno, NULL);
-	Assert(ClogCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+	Assert(!ClogCtl->shared->page_dirty[slotno]);
 
 	LWLockRelease(CLogControlLock);
 }
@@ -246,7 +246,7 @@ StartupCLOG(void)
 		/* Zero the rest of the page */
 		MemSet(byteptr + 1, 0, BLCKSZ - byteno - 1);
 
-		ClogCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
+		ClogCtl->shared->page_dirty[slotno] = true;
 	}
 
 	LWLockRelease(CLogControlLock);
@@ -404,7 +404,7 @@ clog_redo(XLogRecPtr lsn, XLogRecord *record)
 
 		slotno = ZeroCLOGPage(pageno, false);
 		SimpleLruWritePage(ClogCtl, slotno, NULL);
-		Assert(ClogCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+		Assert(!ClogCtl->shared->page_dirty[slotno]);
 
 		LWLockRelease(CLogControlLock);
 	}

src/backend/access/transam/multixact.c

@@ -42,7 +42,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.11 2005/10/28 19:00:19 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.12 2005/11/05 21:19:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -714,7 +714,7 @@ RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
 
 	*offptr = offset;
 
-	MultiXactOffsetCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
+	MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
 
 	/* Exchange our lock */
 	LWLockRelease(MultiXactOffsetControlLock);
@@ -742,7 +742,7 @@ RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
 
 		*memberptr = xids[i];
 
-		MultiXactMemberCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
+		MultiXactMemberCtl->shared->page_dirty[slotno] = true;
 	}
 
 	LWLockRelease(MultiXactMemberControlLock);
@@ -1308,7 +1308,7 @@ BootStrapMultiXact(void)
 
 	/* Make sure it's written out */
 	SimpleLruWritePage(MultiXactOffsetCtl, slotno, NULL);
-	Assert(MultiXactOffsetCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+	Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
 
 	LWLockRelease(MultiXactOffsetControlLock);
 
@@ -1319,7 +1319,7 @@ BootStrapMultiXact(void)
 
 	/* Make sure it's written out */
 	SimpleLruWritePage(MultiXactMemberCtl, slotno, NULL);
-	Assert(MultiXactMemberCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+	Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
 
 	LWLockRelease(MultiXactMemberControlLock);
 }
@@ -1405,7 +1405,7 @@ StartupMultiXact(void)
 
 		MemSet(offptr, 0, BLCKSZ - (entryno * sizeof(MultiXactOffset)));
 
-		MultiXactOffsetCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
+		MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
 	}
 
 	LWLockRelease(MultiXactOffsetControlLock);
@@ -1435,7 +1435,7 @@ StartupMultiXact(void)
 
 		MemSet(xidptr, 0, BLCKSZ - (entryno * sizeof(TransactionId)));
 
-		MultiXactMemberCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
+		MultiXactMemberCtl->shared->page_dirty[slotno] = true;
 	}
 
 	LWLockRelease(MultiXactMemberControlLock);
@@ -1829,7 +1829,7 @@ multixact_redo(XLogRecPtr lsn, XLogRecord *record)
 
 		slotno = ZeroMultiXactOffsetPage(pageno, false);
 		SimpleLruWritePage(MultiXactOffsetCtl, slotno, NULL);
-		Assert(MultiXactOffsetCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+		Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
 
 		LWLockRelease(MultiXactOffsetControlLock);
 	}
@@ -1844,7 +1844,7 @@ multixact_redo(XLogRecPtr lsn, XLogRecord *record)
 
 		slotno = ZeroMultiXactMemberPage(pageno, false);
 		SimpleLruWritePage(MultiXactMemberCtl, slotno, NULL);
-		Assert(MultiXactMemberCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+		Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
 
 		LWLockRelease(MultiXactMemberControlLock);
 	}

src/backend/access/transam/subtrans.c

@@ -22,7 +22,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.11 2005/10/15 02:49:09 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.12 2005/11/05 21:19:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -86,7 +86,7 @@ SubTransSetParent(TransactionId xid, TransactionId parent)
 
 	*ptr = parent;
 
-	SubTransCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
+	SubTransCtl->shared->page_dirty[slotno] = true;
 
 	LWLockRelease(SubtransControlLock);
 }
@@ -199,7 +199,7 @@ BootStrapSUBTRANS(void)
 
 	/* Make sure it's written out */
 	SimpleLruWritePage(SubTransCtl, slotno, NULL);
-	Assert(SubTransCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
+	Assert(!SubTransCtl->shared->page_dirty[slotno]);
 
 	LWLockRelease(SubtransControlLock);
 }

src/include/access/slru.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/slru.h,v 1.14 2005/10/15 02:49:42 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/slru.h,v 1.15 2005/11/05 21:19:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -23,13 +23,17 @@
  */
 #define NUM_SLRU_BUFFERS	8
 
-/* Page status codes */
+/*
+ * Page status codes.  Note that these do not include the "dirty" bit.
+ * page_dirty can be TRUE only in the VALID or WRITE_IN_PROGRESS states;
+ * in the latter case it implies that the page has been re-dirtied since
+ * the write started.
+ */
 typedef enum
 {
 	SLRU_PAGE_EMPTY,			/* buffer is not in use */
 	SLRU_PAGE_READ_IN_PROGRESS, /* page is being read in */
-	SLRU_PAGE_CLEAN,			/* page is valid and not dirty */
-	SLRU_PAGE_DIRTY,			/* page is valid but needs write */
+	SLRU_PAGE_VALID,			/* page is valid and not being written */
 	SLRU_PAGE_WRITE_IN_PROGRESS /* page is being written out */
 } SlruPageStatus;
 
@@ -48,6 +52,7 @@ typedef struct SlruSharedData
 	 */
 	char	   *page_buffer[NUM_SLRU_BUFFERS];
 	SlruPageStatus page_status[NUM_SLRU_BUFFERS];
+	bool		page_dirty[NUM_SLRU_BUFFERS];
 	int			page_number[NUM_SLRU_BUFFERS];
 	unsigned int page_lru_count[NUM_SLRU_BUFFERS];
 	LWLockId	buffer_locks[NUM_SLRU_BUFFERS];