diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index fa9f1a20763..433a4b4538c 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.192 2005/06/06 17:01:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.193 2005/06/06 20:22:56 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1107,9 +1107,9 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid)
 
 		xlrec.target.node = relation->rd_node;
 		xlrec.target.tid = tup->t_self;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfHeapInsert;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
 		xlhdr.t_natts = tup->t_data->t_natts;
@@ -1121,15 +1121,17 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid)
 		 * decides to write the whole page to the xlog, we don't need to
 		 * store xl_heap_header in the xlog.
 		 */
-		rdata[1].buffer = buffer;
 		rdata[1].data = (char *) &xlhdr;
 		rdata[1].len = SizeOfHeapHeader;
+		rdata[1].buffer = buffer;
+		rdata[1].buffer_std = true;
 		rdata[1].next = &(rdata[2]);
 
-		rdata[2].buffer = buffer;
 		/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
 		rdata[2].data = (char *) tup->t_data + offsetof(HeapTupleHeaderData, t_bits);
 		rdata[2].len = tup->t_len - offsetof(HeapTupleHeaderData, t_bits);
+		rdata[2].buffer = buffer;
+		rdata[2].buffer_std = true;
 		rdata[2].next = NULL;
 
 		/*
@@ -1378,14 +1380,15 @@ l1:
 
 		xlrec.target.node = relation->rd_node;
 		xlrec.target.tid = tp.t_self;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfHeapDelete;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
-		rdata[1].buffer = buffer;
 		rdata[1].data = NULL;
 		rdata[1].len = 0;
+		rdata[1].buffer = buffer;
+		rdata[1].buffer_std = true;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE, rdata);
@@ -2226,14 +2229,15 @@ l3:
 		xlrec.target.node = relation->rd_node;
 		xlrec.target.tid = tuple->t_self;
 		xlrec.shared_lock = (mode == LockTupleShared);
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfHeapLock;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
-		rdata[1].buffer = *buffer;
 		rdata[1].data = NULL;
 		rdata[1].len = 0;
+		rdata[1].buffer = *buffer;
+		rdata[1].buffer_std = true;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK, rdata);
@@ -2330,9 +2334,9 @@ log_heap_clean(Relation reln, Buffer buffer, OffsetNumber *unused, int uncnt)
 	xlrec.node = reln->rd_node;
 	xlrec.block = BufferGetBlockNumber(buffer);
 
-	rdata[0].buffer = InvalidBuffer;
 	rdata[0].data = (char *) &xlrec;
 	rdata[0].len = SizeOfHeapClean;
+	rdata[0].buffer = InvalidBuffer;
 	rdata[0].next = &(rdata[1]);
 
 	/*
@@ -2340,7 +2344,6 @@ log_heap_clean(Relation reln, Buffer buffer, OffsetNumber *unused, int uncnt)
 	 * that it is.	When XLogInsert stores the whole buffer, the offsets
 	 * array need not be stored too.
 	 */
-	rdata[1].buffer = buffer;
 	if (uncnt > 0)
 	{
 		rdata[1].data = (char *) unused;
@@ -2351,6 +2354,8 @@ log_heap_clean(Relation reln, Buffer buffer, OffsetNumber *unused, int uncnt)
 		rdata[1].data = NULL;
 		rdata[1].len = 0;
 	}
+	rdata[1].buffer = buffer;
+	rdata[1].buffer_std = true;
 	rdata[1].next = NULL;
 
 	recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_CLEAN, rdata);
@@ -2388,14 +2393,15 @@ log_heap_update(Relation reln, Buffer oldbuf, ItemPointerData from,
 	xlrec.target.node = reln->rd_node;
 	xlrec.target.tid = from;
 	xlrec.newtid = newtup->t_self;
-	rdata[0].buffer = InvalidBuffer;
 	rdata[0].data = (char *) &xlrec;
 	rdata[0].len = SizeOfHeapUpdate;
+	rdata[0].buffer = InvalidBuffer;
 	rdata[0].next = &(rdata[1]);
 
-	rdata[1].buffer = oldbuf;
 	rdata[1].data = NULL;
 	rdata[1].len = 0;
+	rdata[1].buffer = oldbuf;
+	rdata[1].buffer_std = true;
 	rdata[1].next = &(rdata[2]);
 
 	xlhdr.hdr.t_natts = newtup->t_data->t_natts;
@@ -2420,15 +2426,17 @@ log_heap_update(Relation reln, Buffer oldbuf, ItemPointerData from,
 	 * As with insert records, we need not store the rdata[2] segment if
 	 * we decide to store the whole buffer instead.
 	 */
-	rdata[2].buffer = newbuf;
 	rdata[2].data = (char *) &xlhdr;
 	rdata[2].len = hsize;
+	rdata[2].buffer = newbuf;
+	rdata[2].buffer_std = true;
 	rdata[2].next = &(rdata[3]);
 
-	rdata[3].buffer = newbuf;
 	/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
 	rdata[3].data = (char *) newtup->t_data + offsetof(HeapTupleHeaderData, t_bits);
 	rdata[3].len = newtup->t_len - offsetof(HeapTupleHeaderData, t_bits);
+	rdata[3].buffer = newbuf;
+	rdata[3].buffer_std = true;
 	rdata[3].next = NULL;
 
 	/* If new tuple is the single and first tuple on page... */
diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index 868a91ab3a5..9b9fa44e6ed 100644
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.120 2005/03/21 01:23:59 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.121 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -564,9 +564,9 @@ _bt_insertonpg(Relation rel,
 			xlrec.target.node = rel->rd_node;
 			ItemPointerSet(&(xlrec.target.tid), itup_blkno, itup_off);
 
-			rdata[0].buffer = InvalidBuffer;
 			rdata[0].data = (char *) &xlrec;
 			rdata[0].len = SizeOfBtreeInsert;
+			rdata[0].buffer = InvalidBuffer;
 			rdata[0].next = nextrdata = &(rdata[1]);
 
 			if (BufferIsValid(metabuf))
@@ -576,9 +576,9 @@ _bt_insertonpg(Relation rel,
 				xlmeta.fastroot = metad->btm_fastroot;
 				xlmeta.fastlevel = metad->btm_fastlevel;
 
-				nextrdata->buffer = InvalidBuffer;
 				nextrdata->data = (char *) &xlmeta;
 				nextrdata->len = sizeof(xl_btree_metadata);
+				nextrdata->buffer = InvalidBuffer;
 				nextrdata->next = nextrdata + 1;
 				nextrdata++;
 				xlinfo = XLOG_BTREE_INSERT_META;
@@ -603,6 +603,7 @@ _bt_insertonpg(Relation rel,
 					(sizeof(BTItemData) - sizeof(IndexTupleData));
 			}
 			nextrdata->buffer = buf;
+			nextrdata->buffer_std = true;
 			nextrdata->next = NULL;
 
 			recptr = XLogInsert(RM_BTREE_ID, xlinfo, rdata);
@@ -853,28 +854,29 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
 		xlrec.leftlen = ((PageHeader) leftpage)->pd_special -
 			((PageHeader) leftpage)->pd_upper;
 
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfBtreeSplit;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) leftpage + ((PageHeader) leftpage)->pd_upper;
 		rdata[1].len = xlrec.leftlen;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = &(rdata[2]);
 
-		rdata[2].buffer = InvalidBuffer;
 		rdata[2].data = (char *) rightpage + ((PageHeader) rightpage)->pd_upper;
 		rdata[2].len = ((PageHeader) rightpage)->pd_special -
 			((PageHeader) rightpage)->pd_upper;
+		rdata[2].buffer = InvalidBuffer;
 		rdata[2].next = NULL;
 
 		if (!P_RIGHTMOST(ropaque))
 		{
 			rdata[2].next = &(rdata[3]);
-			rdata[3].buffer = sbuf;
 			rdata[3].data = NULL;
 			rdata[3].len = 0;
+			rdata[3].buffer = sbuf;
+			rdata[3].buffer_std = true;
 			rdata[3].next = NULL;
 		}
 
@@ -1464,19 +1466,19 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
 		xlrec.rootblk = rootblknum;
 		xlrec.level = metad->btm_level;
 
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfBtreeNewroot;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
 		/*
 		 * Direct access to page is not good but faster - we should
 		 * implement some new func in page API.
 		 */
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) rootpage + ((PageHeader) rootpage)->pd_upper;
 		rdata[1].len = ((PageHeader) rootpage)->pd_special -
 			((PageHeader) rootpage)->pd_upper;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_NEWROOT, rdata);
diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index b9d42bad6d2..f3ce5bd64a9 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.85 2005/06/02 05:55:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.86 2005/06/06 20:22:57 tgl Exp $
  *
  *	NOTES
  *	   Postgres btree pages look like ordinary relation pages.	The opaque
@@ -74,9 +74,9 @@ _bt_metapinit(Relation rel)
 		xlrec.meta.fastroot = metad->btm_fastroot;
 		xlrec.meta.fastlevel = metad->btm_fastlevel;
 
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfBtreeNewmeta;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = NULL;
 
 		recptr = XLogInsert(RM_BTREE_ID,
@@ -248,9 +248,9 @@ _bt_getroot(Relation rel, int access)
 			xlrec.rootblk = rootblkno;
 			xlrec.level = 0;
 
-			rdata.buffer = InvalidBuffer;
 			rdata.data = (char *) &xlrec;
 			rdata.len = SizeOfBtreeNewroot;
+			rdata.buffer = InvalidBuffer;
 			rdata.next = NULL;
 
 			recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_NEWROOT, &rdata);
@@ -666,9 +666,9 @@ _bt_delitems(Relation rel, Buffer buf,
 		xlrec.node = rel->rd_node;
 		xlrec.block = BufferGetBlockNumber(buf);
 
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfBtreeDelete;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
 		/*
@@ -676,7 +676,6 @@ _bt_delitems(Relation rel, Buffer buf,
 		 * it is.  When XLogInsert stores the whole buffer, the offsets
 		 * array need not be stored too.
 		 */
-		rdata[1].buffer = buf;
 		if (nitems > 0)
 		{
 			rdata[1].data = (char *) itemnos;
@@ -687,6 +686,8 @@ _bt_delitems(Relation rel, Buffer buf,
 			rdata[1].data = NULL;
 			rdata[1].len = 0;
 		}
+		rdata[1].buffer = buf;
+		rdata[1].buffer_std = true;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DELETE, rdata);
@@ -1038,9 +1039,9 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full)
 		xlrec.leftblk = leftsib;
 		xlrec.rightblk = rightsib;
 
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfBtreeDeletePage;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = nextrdata = &(rdata[1]);
 
 		if (BufferIsValid(metabuf))
@@ -1050,9 +1051,9 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full)
 			xlmeta.fastroot = metad->btm_fastroot;
 			xlmeta.fastlevel = metad->btm_fastlevel;
 
-			nextrdata->buffer = InvalidBuffer;
 			nextrdata->data = (char *) &xlmeta;
 			nextrdata->len = sizeof(xl_btree_metadata);
+			nextrdata->buffer = InvalidBuffer;
 			nextrdata->next = nextrdata + 1;
 			nextrdata++;
 			xlinfo = XLOG_BTREE_DELETE_PAGE_META;
@@ -1060,24 +1061,27 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full)
 		else
 			xlinfo = XLOG_BTREE_DELETE_PAGE;
 
-		nextrdata->buffer = pbuf;
 		nextrdata->data = NULL;
 		nextrdata->len = 0;
 		nextrdata->next = nextrdata + 1;
+		nextrdata->buffer = pbuf;
+		nextrdata->buffer_std = true;
 		nextrdata++;
 
-		nextrdata->buffer = rbuf;
 		nextrdata->data = NULL;
 		nextrdata->len = 0;
+		nextrdata->buffer = rbuf;
+		nextrdata->buffer_std = true;
 		nextrdata->next = NULL;
 
 		if (BufferIsValid(lbuf))
 		{
 			nextrdata->next = nextrdata + 1;
 			nextrdata++;
-			nextrdata->buffer = lbuf;
 			nextrdata->data = NULL;
 			nextrdata->len = 0;
+			nextrdata->buffer = lbuf;
+			nextrdata->buffer_std = true;
 			nextrdata->next = NULL;
 		}
 
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 01104015118..115708b7809 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -56,7 +56,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsort.c,v 1.90 2004/12/31 21:59:22 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsort.c,v 1.91 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -287,14 +287,14 @@ _bt_blwritepage(BTWriteState *wstate, Page page, BlockNumber blkno)
 		xlrec.node = wstate->index->rd_node;
 		xlrec.blkno = blkno;
 
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = SizeOfHeapNewpage;
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) page;
 		rdata[1].len = BLCKSZ;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_NEWPAGE, rdata);
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
index 73362330c10..2da835dbbe5 100644
--- a/src/backend/access/transam/clog.c
+++ b/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 1.29 2005/06/06 17:01:22 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.30 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -379,9 +379,9 @@ WriteZeroPageXlogRec(int pageno)
 {
 	XLogRecData rdata;
 
-	rdata.buffer = InvalidBuffer;
 	rdata.data = (char *) (&pageno);
 	rdata.len = sizeof(int);
+	rdata.buffer = InvalidBuffer;
 	rdata.next = NULL;
 	(void) XLogInsert(RM_CLOG_ID, CLOG_ZEROPAGE | XLOG_NO_TRAN, &rdata);
 }
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 3eb58a96a8d..040a4ab0b79 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.203 2005/06/06 17:01:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.204 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -719,25 +719,25 @@ RecordTransactionCommit(void)
 			xlrec.xtime = time(NULL);
 			xlrec.nrels = nrels;
 			xlrec.nsubxacts = nchildren;
-			rdata[0].buffer = InvalidBuffer;
 			rdata[0].data = (char *) (&xlrec);
 			rdata[0].len = MinSizeOfXactCommit;
+			rdata[0].buffer = InvalidBuffer;
 			/* dump rels to delete */
 			if (nrels > 0)
 			{
 				rdata[0].next = &(rdata[1]);
-				rdata[1].buffer = InvalidBuffer;
 				rdata[1].data = (char *) rptr;
 				rdata[1].len = nrels * sizeof(RelFileNode);
+				rdata[1].buffer = InvalidBuffer;
 				lastrdata = 1;
 			}
 			/* dump committed child Xids */
 			if (nchildren > 0)
 			{
 				rdata[lastrdata].next = &(rdata[2]);
-				rdata[2].buffer = InvalidBuffer;
 				rdata[2].data = (char *) children;
 				rdata[2].len = nchildren * sizeof(TransactionId);
+				rdata[2].buffer = InvalidBuffer;
 				lastrdata = 2;
 			}
 			rdata[lastrdata].next = NULL;
@@ -1019,25 +1019,25 @@ RecordTransactionAbort(void)
 			xlrec.xtime = time(NULL);
 			xlrec.nrels = nrels;
 			xlrec.nsubxacts = nchildren;
-			rdata[0].buffer = InvalidBuffer;
 			rdata[0].data = (char *) (&xlrec);
 			rdata[0].len = MinSizeOfXactAbort;
+			rdata[0].buffer = InvalidBuffer;
 			/* dump rels to delete */
 			if (nrels > 0)
 			{
 				rdata[0].next = &(rdata[1]);
-				rdata[1].buffer = InvalidBuffer;
 				rdata[1].data = (char *) rptr;
 				rdata[1].len = nrels * sizeof(RelFileNode);
+				rdata[1].buffer = InvalidBuffer;
 				lastrdata = 1;
 			}
 			/* dump committed child Xids */
 			if (nchildren > 0)
 			{
 				rdata[lastrdata].next = &(rdata[2]);
-				rdata[2].buffer = InvalidBuffer;
 				rdata[2].data = (char *) children;
 				rdata[2].len = nchildren * sizeof(TransactionId);
+				rdata[2].buffer = InvalidBuffer;
 				lastrdata = 2;
 			}
 			rdata[lastrdata].next = NULL;
@@ -1205,25 +1205,25 @@ RecordSubTransactionAbort(void)
 			xlrec.xtime = time(NULL);
 			xlrec.nrels = nrels;
 			xlrec.nsubxacts = nchildren;
-			rdata[0].buffer = InvalidBuffer;
 			rdata[0].data = (char *) (&xlrec);
 			rdata[0].len = MinSizeOfXactAbort;
+			rdata[0].buffer = InvalidBuffer;
 			/* dump rels to delete */
 			if (nrels > 0)
 			{
 				rdata[0].next = &(rdata[1]);
-				rdata[1].buffer = InvalidBuffer;
 				rdata[1].data = (char *) rptr;
 				rdata[1].len = nrels * sizeof(RelFileNode);
+				rdata[1].buffer = InvalidBuffer;
 				lastrdata = 1;
 			}
 			/* dump committed child Xids */
 			if (nchildren > 0)
 			{
 				rdata[lastrdata].next = &(rdata[2]);
-				rdata[2].buffer = InvalidBuffer;
 				rdata[2].data = (char *) children;
 				rdata[2].len = nchildren * sizeof(TransactionId);
+				rdata[2].buffer = InvalidBuffer;
 				lastrdata = 2;
 			}
 			rdata[lastrdata].next = NULL;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index c1609356d39..aa37244162a 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * 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/xlog.c,v 1.196 2005/06/06 17:01:23 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.197 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -434,7 +434,8 @@ static void exitArchiveRecovery(TimeLineID endTLI,
 					uint32 endLogId, uint32 endLogSeg);
 static bool recoveryStopsHere(XLogRecord *record, bool *includeThis);
 
-static void SetBkpBlock(BkpBlock *bkpb, Buffer buffer);
+static bool XLogCheckBuffer(XLogRecData *rdata,
+							XLogRecPtr *lsn, BkpBlock *bkpb);
 static bool AdvanceXLInsertBuffer(void);
 static void XLogWrite(XLogwrtRqst WriteRqst);
 static int XLogFileInit(uint32 log, uint32 seg,
@@ -473,7 +474,7 @@ static void remove_backup_label(void);
 /*
  * Insert an XLOG record having the specified RMID and info bytes,
  * with the body of the record being the data chunk(s) described by
- * the rdata list (see xlog.h for notes about rdata).
+ * the rdata chain (see xlog.h for notes about rdata).
  *
  * Returns XLOG pointer to end of record (beginning of next record).
  * This can be used as LSN for data pages affected by the logged action.
@@ -532,7 +533,7 @@ XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata)
 	}
 
 	/*
-	 * Here we scan the rdata list, determine which buffers must be backed
+	 * Here we scan the rdata chain, determine which buffers must be backed
 	 * up, and compute the CRC values for the data.  Note that the record
 	 * header isn't added into the CRC initially since we don't know the
 	 * final length or info bits quite yet.  Thus, the CRC will represent
@@ -543,13 +544,13 @@ XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata)
 	 * below. We could prevent the race by doing all this work while
 	 * holding the insert lock, but it seems better to avoid doing CRC
 	 * calculations while holding the lock.  This means we have to be
-	 * careful about modifying the rdata list until we know we aren't
+	 * careful about modifying the rdata chain until we know we aren't
 	 * going to loop back again.  The only change we allow ourselves to
-	 * make earlier is to set rdt->data = NULL in list items we have
+	 * make earlier is to set rdt->data = NULL in chain items we have
 	 * decided we will have to back up the whole buffer for.  This is OK
 	 * because we will certainly decide the same thing again for those
 	 * items if we do it over; doing it here saves an extra pass over the
-	 * list later.
+	 * chain later.
 	 */
 begin:;
 	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
@@ -575,7 +576,7 @@ begin:;
 			{
 				if (rdt->buffer == dtbuf[i])
 				{
-					/* Buffer already referenced by earlier list item */
+					/* Buffer already referenced by earlier chain item */
 					if (dtbuf_bkp[i])
 						rdt->data = NULL;
 					else if (rdt->data)
@@ -589,15 +590,9 @@ begin:;
 				{
 					/* OK, put it in this slot */
 					dtbuf[i] = rdt->buffer;
-
-					/*
-					 * XXX We assume page LSN is first data on page
-					 */
-					dtbuf_lsn[i] = *((XLogRecPtr *) BufferGetBlock(rdt->buffer));
-					if (XLByteLE(dtbuf_lsn[i], RedoRecPtr))
+					if (XLogCheckBuffer(rdt, &(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
 					{
 						dtbuf_bkp[i] = true;
-						SetBkpBlock(&(dtbuf_xlg[i]), rdt->buffer);
 						rdt->data = NULL;
 					}
 					else if (rdt->data)
@@ -612,7 +607,7 @@ begin:;
 				elog(PANIC, "can backup at most %d blocks per xlog record",
 					 XLR_MAX_BKP_BLOCKS);
 		}
-		/* Break out of loop when rdt points to last list item */
+		/* Break out of loop when rdt points to last chain item */
 		if (rdt->next == NULL)
 			break;
 		rdt = rdt->next;
@@ -726,15 +721,15 @@ begin:;
 	}
 
 	/*
-	 * Make additional rdata list entries for the backup blocks, so that
+	 * Make additional rdata chain entries for the backup blocks, so that
 	 * we don't need to special-case them in the write loop.  Note that we
-	 * have now irrevocably changed the input rdata list.  At the exit of
+	 * have now irrevocably changed the input rdata chain.  At the exit of
 	 * this loop, write_len includes the backup block data.
 	 *
 	 * Also set the appropriate info bits to show which buffers were backed
 	 * up.	The i'th XLR_SET_BKP_BLOCK bit corresponds to the i'th
 	 * distinct buffer value (ignoring InvalidBuffer) appearing in the
-	 * rdata list.
+	 * rdata chain.
 	 */
 	write_len = len;
 	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
@@ -742,7 +737,7 @@ begin:;
 		BkpBlock   *bkpb;
 		char	   *page;
 
-		if (dtbuf[i] == InvalidBuffer || !(dtbuf_bkp[i]))
+		if (!dtbuf_bkp[i])
 			continue;
 
 		info |= XLR_SET_BKP_BLOCK(i);
@@ -938,43 +933,64 @@ begin:;
 }
 
 /*
- * Fill a BkpBlock struct given a buffer containing the page to be saved
- *
- * This is nontrivial only because it has to decide whether to apply "hole
- * compression".
+ * Determine whether the buffer referenced by an XLogRecData item has to
+ * be backed up, and if so fill a BkpBlock struct for it.  In any case
+ * save the buffer's LSN at *lsn.
  */
-static void
-SetBkpBlock(BkpBlock *bkpb, Buffer buffer)
+static bool
+XLogCheckBuffer(XLogRecData *rdata,
+				XLogRecPtr *lsn, BkpBlock *bkpb)
 {
 	PageHeader	page;
-	uint16		offset;
-	uint16		length;
 
-	/* Save page identity info */
-	bkpb->node = BufferGetFileNode(buffer);
-	bkpb->block = BufferGetBlockNumber(buffer);
+	page = (PageHeader) BufferGetBlock(rdata->buffer);
 
-	/* Test whether there is a "hole" containing zeroes in the page */
-	page = (PageHeader) BufferGetBlock(buffer);
-	offset = page->pd_lower;
-	/* Check if pd_lower appears sane at all */
-	if (offset >= SizeOfPageHeaderData && offset < BLCKSZ)
+	/*
+	 * XXX We assume page LSN is first data on *every* page that can be
+	 * passed to XLogInsert, whether it otherwise has the standard page
+	 * layout or not.
+	 */
+	*lsn = page->pd_lsn;
+
+	if (XLByteLE(page->pd_lsn, RedoRecPtr))
 	{
-		char   *spd = (char *) page + offset;
-		char   *epd = (char *) page + BLCKSZ;
-		char   *pd = spd;
+		/*
+		 * The page needs to be backed up, so set up *bkpb
+		 */
+		bkpb->node = BufferGetFileNode(rdata->buffer);
+		bkpb->block = BufferGetBlockNumber(rdata->buffer);
 
-		while (pd < epd && *pd == '\0')
-			pd++;
+		if (rdata->buffer_std)
+		{
+			/* Assume we can omit data between pd_lower and pd_upper */
+			uint16		lower = page->pd_lower;
+			uint16		upper = page->pd_upper;
 
-		length = pd - spd;
-		if (length == 0)
-			offset = 0;
+			if (lower >= SizeOfPageHeaderData &&
+				upper > lower &&
+				upper <= BLCKSZ)
+			{
+				bkpb->hole_offset = lower;
+				bkpb->hole_length = upper - lower;
+			}
+			else
+			{
+				/* No "hole" to compress out */
+				bkpb->hole_offset = 0;
+				bkpb->hole_length = 0;
+			}
+		}
+		else
+		{
+			/* Not a standard page header, don't try to eliminate "hole" */
+			bkpb->hole_offset = 0;
+			bkpb->hole_length = 0;
+		}
+
+		return true;			/* buffer requires backup */
 	}
-	else
-		offset = length = 0;
-	bkpb->hole_offset = offset;
-	bkpb->hole_length = length;
+
+	return false;				/* buffer does not need to be backed up */
 }
 
 /*
@@ -5093,9 +5109,9 @@ CreateCheckPoint(bool shutdown, bool force)
 	/*
 	 * Now insert the checkpoint record into XLOG.
 	 */
-	rdata.buffer = InvalidBuffer;
 	rdata.data = (char *) (&checkPoint);
 	rdata.len = sizeof(checkPoint);
+	rdata.buffer = InvalidBuffer;
 	rdata.next = NULL;
 
 	recptr = XLogInsert(RM_XLOG_ID,
@@ -5197,9 +5213,9 @@ XLogPutNextOid(Oid nextOid)
 {
 	XLogRecData rdata;
 
-	rdata.buffer = InvalidBuffer;
 	rdata.data = (char *) (&nextOid);
 	rdata.len = sizeof(Oid);
+	rdata.buffer = InvalidBuffer;
 	rdata.next = NULL;
 	(void) XLogInsert(RM_XLOG_ID, XLOG_NEXTOID, &rdata);
 	/*
@@ -5220,9 +5236,9 @@ XLogPutNextMultiXactId(MultiXactId nextMulti)
 {
 	XLogRecData rdata;
 
-	rdata.buffer = InvalidBuffer;
 	rdata.data = (char *) (&nextMulti);
 	rdata.len = sizeof(MultiXactId);
+	rdata.buffer = InvalidBuffer;
 	rdata.next = NULL;
 	(void) XLogInsert(RM_XLOG_ID, XLOG_NEXTMULTI, &rdata);
 	/*
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 370977c6586..40cfb3e6586 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.158 2005/06/06 17:01:23 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.159 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -444,9 +444,9 @@ createdb(const CreatedbStmt *stmt)
 			xlrec.src_db_id = src_dboid;
 			xlrec.src_tablespace_id = srctablespace;
 
-			rdata[0].buffer = InvalidBuffer;
 			rdata[0].data = (char *) &xlrec;
 			rdata[0].len = sizeof(xl_dbase_create_rec);
+			rdata[0].buffer = InvalidBuffer;
 			rdata[0].next = NULL;
 
 			(void) XLogInsert(RM_DBASE_ID, XLOG_DBASE_CREATE, rdata);
@@ -1074,9 +1074,9 @@ remove_dbtablespaces(Oid db_id)
 			xlrec.db_id = db_id;
 			xlrec.tablespace_id = dsttablespace;
 
-			rdata[0].buffer = InvalidBuffer;
 			rdata[0].data = (char *) &xlrec;
 			rdata[0].len = sizeof(xl_dbase_drop_rec);
+			rdata[0].buffer = InvalidBuffer;
 			rdata[0].next = NULL;
 
 			(void) XLogInsert(RM_DBASE_ID, XLOG_DBASE_DROP, rdata);
diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 3278be1239f..78b9225b83c 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.121 2005/06/06 17:01:23 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.122 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -264,14 +264,14 @@ DefineSequence(CreateSeqStmt *seq)
 		newseq->log_cnt = 0;
 
 		xlrec.node = rel->rd_node;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = sizeof(xl_seq_rec);
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) tuple->t_data;
 		rdata[1].len = tuple->t_len;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG | XLOG_NO_TRAN, rdata);
@@ -338,15 +338,15 @@ AlterSequence(AlterSeqStmt *stmt)
 		XLogRecData rdata[2];
 
 		xlrec.node = seqrel->rd_node;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = sizeof(xl_seq_rec);
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) page + ((PageHeader) page)->pd_upper;
 		rdata[1].len = ((PageHeader) page)->pd_special -
 			((PageHeader) page)->pd_upper;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG | XLOG_NO_TRAN, rdata);
@@ -531,9 +531,9 @@ nextval(PG_FUNCTION_ARGS)
 		XLogRecData rdata[2];
 
 		xlrec.node = seqrel->rd_node;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = sizeof(xl_seq_rec);
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
 		/* set values that will be saved in xlog */
@@ -541,10 +541,10 @@ nextval(PG_FUNCTION_ARGS)
 		seq->is_called = true;
 		seq->log_cnt = 0;
 
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) page + ((PageHeader) page)->pd_upper;
 		rdata[1].len = ((PageHeader) page)->pd_special -
 			((PageHeader) page)->pd_upper;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG | XLOG_NO_TRAN, rdata);
@@ -666,9 +666,9 @@ do_setval(RangeVar *sequence, int64 next, bool iscalled)
 		Page		page = BufferGetPage(buf);
 
 		xlrec.node = seqrel->rd_node;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = sizeof(xl_seq_rec);
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
 		/* set values that will be saved in xlog */
@@ -676,10 +676,10 @@ do_setval(RangeVar *sequence, int64 next, bool iscalled)
 		seq->is_called = true;
 		seq->log_cnt = 0;
 
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) page + ((PageHeader) page)->pd_upper;
 		rdata[1].len = ((PageHeader) page)->pd_special -
 			((PageHeader) page)->pd_upper;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
 		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG | XLOG_NO_TRAN, rdata);
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index c7669dfc58f..9981129c0eb 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.160 2005/06/05 00:38:08 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.161 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -5667,14 +5667,14 @@ copy_relation_data(Relation rel, SMgrRelation dst)
 			xlrec.node = dst->smgr_rnode;
 			xlrec.blkno = blkno;
 
-			rdata[0].buffer = InvalidBuffer;
 			rdata[0].data = (char *) &xlrec;
 			rdata[0].len = SizeOfHeapNewpage;
+			rdata[0].buffer = InvalidBuffer;
 			rdata[0].next = &(rdata[1]);
 
-			rdata[1].buffer = InvalidBuffer;
 			rdata[1].data = (char *) page;
 			rdata[1].len = BLCKSZ;
+			rdata[1].buffer = InvalidBuffer;
 			rdata[1].next = NULL;
 
 			recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_NEWPAGE, rdata);
diff --git a/src/backend/commands/tablespace.c b/src/backend/commands/tablespace.c
index f9041a0a643..fac20708c0d 100644
--- a/src/backend/commands/tablespace.c
+++ b/src/backend/commands/tablespace.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablespace.c,v 1.20 2005/06/06 17:01:23 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablespace.c,v 1.21 2005/06/06 20:22:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -356,14 +356,14 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 		XLogRecData rdata[2];
 
 		xlrec.ts_id = tablespaceoid;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = offsetof(xl_tblspc_create_rec, ts_path);
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = &(rdata[1]);
 
-		rdata[1].buffer = InvalidBuffer;
 		rdata[1].data = (char *) location;
 		rdata[1].len = strlen(location) + 1;
+		rdata[1].buffer = InvalidBuffer;
 		rdata[1].next = NULL;
 
 		(void) XLogInsert(RM_TBLSPC_ID, XLOG_TBLSPC_CREATE, rdata);
@@ -461,9 +461,9 @@ DropTableSpace(DropTableSpaceStmt *stmt)
 		XLogRecData rdata[1];
 
 		xlrec.ts_id = tablespaceoid;
-		rdata[0].buffer = InvalidBuffer;
 		rdata[0].data = (char *) &xlrec;
 		rdata[0].len = sizeof(xl_tblspc_drop_rec);
+		rdata[0].buffer = InvalidBuffer;
 		rdata[0].next = NULL;
 
 		(void) XLogInsert(RM_TBLSPC_ID, XLOG_TBLSPC_DROP, rdata);
diff --git a/src/backend/storage/page/bufpage.c b/src/backend/storage/page/bufpage.c
index 8f8ba9e0d2b..5b3f7bee95f 100644
--- a/src/backend/storage/page/bufpage.c
+++ b/src/backend/storage/page/bufpage.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.64 2005/06/02 05:55:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.65 2005/06/06 20:22:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -357,7 +357,7 @@ PageRepairFragmentation(Page page, OffsetNumber *unused)
 			lp = PageGetItemId(page, i + 1);
 			lp->lp_len = 0;		/* indicate unused & deallocated */
 		}
-		((PageHeader) page)->pd_upper = pd_upper = pd_special;
+		((PageHeader) page)->pd_upper = pd_special;
 	}
 	else
 	{							/* nused != 0 */
@@ -411,17 +411,11 @@ PageRepairFragmentation(Page page, OffsetNumber *unused)
 			lp->lp_off = upper;
 		}
 
-		((PageHeader) page)->pd_upper = pd_upper = upper;
+		((PageHeader) page)->pd_upper = upper;
 
 		pfree(itemidbase);
 	}
 
-	/*
-	 * Zero out the now-free space.  This is not essential, but it allows
-	 * xlog.c to compress WAL data better.
-	 */
-	MemSet((char *) page + pd_lower, 0, pd_upper - pd_lower);
-
 	return (nline - nused);
 }
 
@@ -531,13 +525,6 @@ PageIndexTupleDelete(Page page, OffsetNumber offnum)
 	phdr->pd_upper += size;
 	phdr->pd_lower -= sizeof(ItemIdData);
 
-	/*
-	 * Zero out the just-freed space.  This is not essential, but it allows
-	 * xlog.c to compress WAL data better.
-	 */
-	MemSet((char *) page + phdr->pd_lower, 0, sizeof(ItemIdData));
-	MemSet(addr, 0, size);
-
 	/*
 	 * Finally, we need to adjust the linp entries that remain.
 	 *
@@ -685,14 +672,8 @@ PageIndexMultiDelete(Page page, OffsetNumber *itemnos, int nitems)
 		lp->lp_off = upper;
 	}
 
-	phdr->pd_lower = pd_lower = SizeOfPageHeaderData + nused * sizeof(ItemIdData);
-	phdr->pd_upper = pd_upper = upper;
-
-	/*
-	 * Zero out the now-free space.  This is not essential, but it allows
-	 * xlog.c to compress WAL data better.
-	 */
-	MemSet((char *) page + pd_lower, 0, pd_upper - pd_lower);
+	phdr->pd_lower = SizeOfPageHeaderData + nused * sizeof(ItemIdData);
+	phdr->pd_upper = upper;
 
 	pfree(itemidbase);
 }
diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c
index ca171a3b1a2..13ad72a3755 100644
--- a/src/backend/storage/smgr/smgr.c
+++ b/src/backend/storage/smgr/smgr.c
@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.88 2005/06/06 17:01:24 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.89 2005/06/06 20:22:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -370,9 +370,9 @@ smgrcreate(SMgrRelation reln, bool isTemp, bool isRedo)
 	 */
 	xlrec.rnode = reln->smgr_rnode;
 
-	rdata.buffer = InvalidBuffer;
 	rdata.data = (char *) &xlrec;
 	rdata.len = sizeof(xlrec);
+	rdata.buffer = InvalidBuffer;
 	rdata.next = NULL;
 
 	lsn = XLogInsert(RM_SMGR_ID, XLOG_SMGR_CREATE | XLOG_NO_TRAN, &rdata);
@@ -635,9 +635,9 @@ smgrtruncate(SMgrRelation reln, BlockNumber nblocks, bool isTemp)
 		xlrec.blkno = newblks;
 		xlrec.rnode = reln->smgr_rnode;
 
-		rdata.buffer = InvalidBuffer;
 		rdata.data = (char *) &xlrec;
 		rdata.len = sizeof(xlrec);
+		rdata.buffer = InvalidBuffer;
 		rdata.next = NULL;
 
 		lsn = XLogInsert(RM_SMGR_ID, XLOG_SMGR_TRUNCATE | XLOG_NO_TRAN,
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 554c3c3aec7..7547d7f5b9f 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.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/xlog.h,v 1.63 2005/06/06 17:01:24 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.64 2005/06/06 20:22:58 tgl Exp $
  */
 #ifndef XLOG_H
 #define XLOG_H
@@ -91,24 +91,42 @@ typedef struct XLogRecord
 extern int	sync_method;
 
 /*
- * List of these structs is used to pass data to XLogInsert().
+ * The rmgr data to be written by XLogInsert() is defined by a chain of
+ * one or more XLogRecData structs.  (Multiple structs would be used when
+ * parts of the source data aren't physically adjacent in memory, or when
+ * multiple associated buffers need to be specified.)
  *
  * If buffer is valid then XLOG will check if buffer must be backed up
  * (ie, whether this is first change of that page since last checkpoint).
  * If so, the whole page contents are attached to the XLOG record, and XLOG
  * sets XLR_BKP_BLOCK_X bit in xl_info.  Note that the buffer must be pinned
- * and locked while this is going on, so that it won't change under us.
- * NB: when this happens, we do not bother to insert the associated data into
- * the XLOG record, since we assume it's present in the buffer.  Therefore,
- * rmgr redo routines MUST pay attention to XLR_BKP_BLOCK_X to know what
- * is actually stored in the XLOG record.
+ * and exclusive-locked by the caller, so that it won't change under us.
+ * NB: when the buffer is backed up, we DO NOT insert the data pointed to by
+ * this XLogRecData struct into the XLOG record, since we assume it's present
+ * in the buffer.  Therefore, rmgr redo routines MUST pay attention to
+ * XLR_BKP_BLOCK_X to know what is actually stored in the XLOG record.
+ * The i'th XLR_BKP_BLOCK bit corresponds to the i'th distinct buffer
+ * value (ignoring InvalidBuffer) appearing in the rdata chain.
+ *
+ * When buffer is valid, caller must set buffer_std to indicate whether the
+ * page uses standard pd_lower/pd_upper header fields.  If this is true, then
+ * XLOG is allowed to omit the free space between pd_lower and pd_upper from
+ * the backed-up page image.  Note that even when buffer_std is false, the
+ * page MUST have an LSN field as its first eight bytes!
+ *
+ * Note: data can be NULL to indicate no rmgr data associated with this chain
+ * entry.  This can be sensible (ie, not a wasted entry) if buffer is valid.
+ * The implication is that the buffer has been changed by the operation being
+ * logged, and so may need to be backed up, but the change can be redone using
+ * only information already present elsewhere in the XLOG entry.
  */
 typedef struct XLogRecData
 {
-	Buffer		buffer;			/* buffer associated with this data */
-	char	   *data;
-	uint32		len;
-	struct XLogRecData *next;
+	char	   *data;			/* start of rmgr data to include */
+	uint32		len;			/* length of rmgr data to include */
+	Buffer		buffer;			/* buffer associated with data, if any */
+	bool		buffer_std;		/* buffer has standard pd_lower/pd_upper */
+	struct XLogRecData *next;	/* next struct in chain, or NULL */
 } XLogRecData;
 
 extern TimeLineID ThisTimeLineID;		/* current TLI */