diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index 775eaca242..5f8be398ca 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 1.156 2007/04/11 20:47:37 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.157 2007/05/20 21:08:19 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1034,21 +1034,23 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
 		 * Log the new item and its offset, if it was inserted on the left
 		 * page. (If it was put on the right page, we don't need to explicitly
 		 * WAL log it because it's included with all the other items on the
-		 * right page.) Show these as belonging to the left page buffer,
-		 * so that they are not stored if XLogInsert decides it needs a
-		 * full-page image of the left page.
+		 * right page.) Show the new item as belonging to the left page buffer,
+		 * so that it is not stored if XLogInsert decides it needs a full-page
+		 * image of the left page.  We store the offset anyway, though, to
+		 * support archive compression of these records.
 		 */
 		if (newitemonleft)
 		{
 			lastrdata->next = lastrdata + 1;
 			lastrdata++;
+
 			lastrdata->data = (char *) &newitemoff;
 			lastrdata->len = sizeof(OffsetNumber);
-			lastrdata->buffer = buf;		/* backup block 1 */
-			lastrdata->buffer_std = true;
+			lastrdata->buffer = InvalidBuffer;
 
 			lastrdata->next = lastrdata + 1;
 			lastrdata++;
+
 			lastrdata->data = (char *) newitem;
 			lastrdata->len = MAXALIGN(newitemsz);
 			lastrdata->buffer = buf;		/* backup block 1 */
@@ -1064,6 +1066,7 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
 			 */
 			lastrdata->next = lastrdata + 1;
 			lastrdata++;
+
 			lastrdata->data = NULL;
 			lastrdata->len = 0;
 			lastrdata->buffer = buf;		/* backup block 1 */
diff --git a/src/backend/access/nbtree/nbtxlog.c b/src/backend/access/nbtree/nbtxlog.c
index ff41be3767..189695853a 100644
--- a/src/backend/access/nbtree/nbtxlog.c
+++ b/src/backend/access/nbtree/nbtxlog.c
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.43 2007/04/11 20:47:38 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtxlog.c,v 1.44 2007/05/20 21:08:19 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -292,14 +292,17 @@ btree_xlog_split(bool onleft, bool isroot,
 	}
 
 	/* Extract newitem and newitemoff, if present */
-	if (onleft && !(record->xl_info & XLR_BKP_BLOCK_1))
+	if (onleft)
 	{
-		IndexTupleData itupdata;
-
 		/* Extract the offset (still assuming 16-bit alignment) */
 		memcpy(&newitemoff, datapos, sizeof(OffsetNumber));
 		datapos += sizeof(OffsetNumber);
 		datalen -= sizeof(OffsetNumber);
+	}
+
+	if (onleft && !(record->xl_info & XLR_BKP_BLOCK_1))
+	{
+		IndexTupleData itupdata;
 
 		/*
 		 * We need to copy the tuple header to apply IndexTupleDSize, because
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 655563a3d8..3dc00499bf 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.268 2007/04/30 21:01:52 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.269 2007/05/20 21:08:19 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -783,6 +783,19 @@ begin:;
 		}
 	}
 
+	/*
+	 * If we backed up any full blocks and online backup is not in progress,
+	 * mark the backup blocks as removable.  This allows the WAL archiver to
+	 * know whether it is safe to compress archived WAL data by transforming
+	 * full-block records into the non-full-block format.
+	 *
+	 * Note: we could just set the flag whenever !forcePageWrites, but
+	 * defining it like this leaves the info bit free for some potential
+	 * other use in records without any backup blocks.
+	 */
+	if ((info & XLR_BKP_BLOCK_MASK) && !Insert->forcePageWrites)
+		info |= XLR_BKP_REMOVABLE;
+
 	/*
 	 * If there isn't enough space on the current XLOG page for a record
 	 * header, advance to the next page (leaving the unused space as zeroes).
@@ -5868,6 +5881,10 @@ xlog_redo(XLogRecPtr lsn, XLogRecord *record)
 
 		RecoveryRestartPoint(&checkPoint);
 	}
+	else if (info == XLOG_NOOP)
+	{
+		/* nothing to do here */
+	}
 	else if (info == XLOG_SWITCH)
 	{
 		/* nothing to do here */
@@ -5894,6 +5911,10 @@ xlog_desc(StringInfo buf, uint8 xl_info, char *rec)
 						 checkpoint->nextMultiOffset,
 				 (info == XLOG_CHECKPOINT_SHUTDOWN) ? "shutdown" : "online");
 	}
+	else if (info == XLOG_NOOP)
+	{
+		appendStringInfo(buf, "xlog no-op");
+	}
 	else if (info == XLOG_NEXTOID)
 	{
 		Oid			nextOid;
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index bb53a04b49..87ff6aba50 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.76 2007/01/05 22:19:51 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.77 2007/05/20 21:08:19 tgl Exp $
  */
 #ifndef XLOG_H
 #define XLOG_H
@@ -66,8 +66,7 @@ typedef struct XLogRecord
 /*
  * If we backed up any disk blocks with the XLOG record, we use flag bits in
  * xl_info to signal it.  We support backup of up to 3 disk blocks per XLOG
- * record.	(Could support 4 if we cared to dedicate all the xl_info bits for
- * this purpose; currently bit 0 of xl_info is unused and available.)
+ * record.
  */
 #define XLR_BKP_BLOCK_MASK		0x0E	/* all info bits used for bkp blocks */
 #define XLR_MAX_BKP_BLOCKS		3
@@ -76,6 +75,15 @@ typedef struct XLogRecord
 #define XLR_BKP_BLOCK_2			XLR_SET_BKP_BLOCK(1)	/* 0x04 */
 #define XLR_BKP_BLOCK_3			XLR_SET_BKP_BLOCK(2)	/* 0x02 */
 
+/*
+ * Bit 0 of xl_info is set if the backed-up blocks could safely be removed
+ * from a compressed version of XLOG (that is, they are backed up only to
+ * prevent partial-page-write problems, and not to ensure consistency of PITR
+ * recovery).  The compression algorithm would need to extract data from the
+ * blocks to create an equivalent non-full-page XLOG record.
+ */
+#define XLR_BKP_REMOVABLE		0x01
+
 /*
  * Sometimes we log records which are out of transaction control.
  * Rmgr may "or" XLOG_NO_TRAN into info passed to XLogInsert to indicate this.
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index cc9c6070bc..c5645b1389 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.20 2007/04/30 21:01:53 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.21 2007/05/20 21:08:19 tgl Exp $
  */
 #ifndef XLOG_INTERNAL_H
 #define XLOG_INTERNAL_H
@@ -71,7 +71,7 @@ typedef struct XLogContRecord
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD061	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD062	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/catalog/pg_control.h b/src/include/catalog/pg_control.h
index 23c2681a8f..8203cc3f81 100644
--- a/src/include/catalog/pg_control.h
+++ b/src/include/catalog/pg_control.h
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_control.h,v 1.37 2007/04/03 04:14:26 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_control.h,v 1.38 2007/05/20 21:08:19 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -44,6 +44,7 @@ typedef struct CheckPoint
 /* XLOG info values for XLOG rmgr */
 #define XLOG_CHECKPOINT_SHUTDOWN		0x00
 #define XLOG_CHECKPOINT_ONLINE			0x10
+#define XLOG_NOOP						0x20
 #define XLOG_NEXTOID					0x30
 #define XLOG_SWITCH						0x40