Make the world safe for full_page_writes. Allow XLOG records that try to

update no-longer-existing pages to fall through as no-ops, but make a note
of each page number referenced by such records.  If we don't see a later
XLOG entry dropping the table or truncating away the page, complain at
the end of XLOG replay.  Since this fixes the known failure mode for
full_page_writes = off, revert my previous band-aid patch that disabled
that GUC variable.

src/backend/access/transam/xlog.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.234 2006/04/05 03:34:05 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.235 2006/04/14 20:27:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -980,7 +980,8 @@ XLogCheckBuffer(XLogRecData *rdata,
 	 */
 	*lsn = page->pd_lsn;
 
-	if (XLByteLE(page->pd_lsn, RedoRecPtr))
+	if (fullPageWrites &&
+		XLByteLE(page->pd_lsn, RedoRecPtr))
 	{
 		/*
 		 * The page needs to be backed up, so set up *bkpb
@@ -4786,6 +4787,12 @@ StartupXLOG(void)
 				RmgrTable[rmid].rm_cleanup();
 		}
 
+		/*
+		 * Check to see if the XLOG sequence contained any unresolved
+		 * references to uninitialized pages.
+		 */
+		XLogCheckInvalidPages();
+
 		/*
 		 * Reset pgstat data, because it may be invalid after recovery.
 		 */

src/backend/access/transam/xlogutils.c

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.43 2006/03/31 23:32:06 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.44 2006/04/14 20:27:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -24,6 +24,176 @@
 #include "utils/hsearch.h"
 
 
+/*
+ * During XLOG replay, we may see XLOG records for incremental updates of
+ * pages that no longer exist, because their relation was later dropped or
+ * truncated.  (Note: this is only possible when full_page_writes = OFF,
+ * since when it's ON, the first reference we see to a page should always
+ * be a full-page rewrite not an incremental update.)  Rather than simply
+ * ignoring such records, we make a note of the referenced page, and then
+ * complain if we don't actually see a drop or truncate covering the page
+ * later in replay.
+ */
+typedef struct xl_invalid_page_key
+{
+	RelFileNode node;			/* the relation */
+	BlockNumber blkno;			/* the page */
+} xl_invalid_page_key;
+
+typedef struct xl_invalid_page
+{
+	xl_invalid_page_key key;	/* hash key ... must be first */
+	bool		present;		/* page existed but contained zeroes */
+} xl_invalid_page;
+
+static HTAB *invalid_page_tab = NULL;
+
+
+/* Log a reference to an invalid page */
+static void
+log_invalid_page(RelFileNode node, BlockNumber blkno, bool present)
+{
+	xl_invalid_page_key key;
+	xl_invalid_page *hentry;
+	bool		found;
+
+	/*
+	 * Log references to invalid pages at DEBUG1 level.  This allows some
+	 * tracing of the cause (note the elog context mechanism will tell us
+	 * something about the XLOG record that generated the reference).
+	 */
+	if (present)
+		elog(DEBUG1, "page %u of relation %u/%u/%u is uninitialized",
+			 blkno, node.spcNode, node.dbNode, node.relNode);
+	else
+		elog(DEBUG1, "page %u of relation %u/%u/%u does not exist",
+			 blkno, node.spcNode, node.dbNode, node.relNode);
+
+	if (invalid_page_tab == NULL)
+	{
+		/* create hash table when first needed */
+		HASHCTL		ctl;
+
+		memset(&ctl, 0, sizeof(ctl));
+		ctl.keysize = sizeof(xl_invalid_page_key);
+		ctl.entrysize = sizeof(xl_invalid_page);
+		ctl.hash = tag_hash;
+
+		invalid_page_tab = hash_create("XLOG invalid-page table",
+									   100,
+									   &ctl,
+									   HASH_ELEM | HASH_FUNCTION);
+	}
+
+	/* we currently assume xl_invalid_page_key contains no padding */
+	key.node = node;
+	key.blkno = blkno;
+	hentry = (xl_invalid_page *)
+		hash_search(invalid_page_tab, (void *) &key, HASH_ENTER, &found);
+
+	if (!found)
+	{
+		/* hash_search already filled in the key */
+		hentry->present = present;
+	}
+	else
+	{
+		/* repeat reference ... leave "present" as it was */
+	}
+}
+
+/* Forget any invalid pages >= minblkno, because they've been dropped */
+static void
+forget_invalid_pages(RelFileNode node, BlockNumber minblkno)
+{
+	HASH_SEQ_STATUS status;
+	xl_invalid_page *hentry;
+
+	if (invalid_page_tab == NULL)
+		return;					/* nothing to do */
+
+	hash_seq_init(&status, invalid_page_tab);
+
+	while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL)
+	{
+		if (RelFileNodeEquals(hentry->key.node, node) &&
+			hentry->key.blkno >= minblkno)
+		{
+			elog(DEBUG2, "page %u of relation %u/%u/%u has been dropped",
+				 hentry->key.blkno, hentry->key.node.spcNode,
+				 hentry->key.node.dbNode, hentry->key.node.relNode);
+
+			if (hash_search(invalid_page_tab,
+							(void *) &hentry->key,
+							HASH_REMOVE, NULL) == NULL)
+				elog(ERROR, "hash table corrupted");
+		}
+	}
+}
+
+/* Forget any invalid pages in a whole database */
+static void
+forget_invalid_pages_db(Oid dbid)
+{
+	HASH_SEQ_STATUS status;
+	xl_invalid_page *hentry;
+
+	if (invalid_page_tab == NULL)
+		return;					/* nothing to do */
+
+	hash_seq_init(&status, invalid_page_tab);
+
+	while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL)
+	{
+		if (hentry->key.node.dbNode == dbid)
+		{
+			elog(DEBUG2, "page %u of relation %u/%u/%u has been dropped",
+				 hentry->key.blkno, hentry->key.node.spcNode,
+				 hentry->key.node.dbNode, hentry->key.node.relNode);
+
+			if (hash_search(invalid_page_tab,
+							(void *) &hentry->key,
+							HASH_REMOVE, NULL) == NULL)
+				elog(ERROR, "hash table corrupted");
+		}
+	}
+}
+
+/* Complain about any remaining invalid-page entries */
+void
+XLogCheckInvalidPages(void)
+{
+	HASH_SEQ_STATUS status;
+	xl_invalid_page *hentry;
+	bool		foundone = false;
+
+	if (invalid_page_tab == NULL)
+		return;					/* nothing to do */
+
+	hash_seq_init(&status, invalid_page_tab);
+
+	/*
+	 * Our strategy is to emit WARNING messages for all remaining entries
+	 * and only PANIC after we've dumped all the available info.
+	 */
+	while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL)
+	{
+		if (hentry->present)
+			elog(WARNING, "page %u of relation %u/%u/%u was uninitialized",
+				 hentry->key.blkno, hentry->key.node.spcNode,
+				 hentry->key.node.dbNode, hentry->key.node.relNode);
+		else
+			elog(WARNING, "page %u of relation %u/%u/%u did not exist",
+				 hentry->key.blkno, hentry->key.node.spcNode,
+				 hentry->key.node.dbNode, hentry->key.node.relNode);
+		foundone = true;
+	}
+
+	if (foundone)
+		elog(PANIC, "WAL contains references to invalid pages");
+}
+
+
 /*
  * XLogReadBuffer
  *		Read a page during XLOG replay
@@ -40,12 +210,11 @@
  * the page being "new" (all zeroes).
  *
  * If "init" is false then the caller needs the page to be valid already.
- * If the page doesn't exist or contains zeroes, we report failure.
- *
- * If the return value is InvalidBuffer (only possible when init = false),
- * the caller should silently skip the update on this page.  This currently
- * never happens, but we retain it as part of the API spec for possible future
- * use.
+ * If the page doesn't exist or contains zeroes, we return InvalidBuffer.
+ * In this case the caller should silently skip the update on this page.
+ * (In this situation, we expect that the page was later dropped or truncated.
+ * If we don't see evidence of that later in the WAL sequence, we'll complain
+ * at the end of WAL replay.)
  */
 Buffer
 XLogReadBuffer(Relation reln, BlockNumber blkno, bool init)
@@ -64,9 +233,10 @@ XLogReadBuffer(Relation reln, BlockNumber blkno, bool init)
 	{
 		/* hm, page doesn't exist in file */
 		if (!init)
-			elog(PANIC, "block %u of relation %u/%u/%u does not exist",
-				 blkno, reln->rd_node.spcNode,
-				 reln->rd_node.dbNode, reln->rd_node.relNode);
+		{
+			log_invalid_page(reln->rd_node, blkno, false);
+			return InvalidBuffer;
+		}
 		/* OK to extend the file */
 		/* we do this in recovery only - no rel-extension lock needed */
 		Assert(InRecovery);
@@ -89,9 +259,11 @@ XLogReadBuffer(Relation reln, BlockNumber blkno, bool init)
 		Page	page = (Page) BufferGetPage(buffer);
 
 		if (PageIsNew((PageHeader) page))
-			elog(PANIC, "block %u of relation %u/%u/%u is uninitialized",
-				 blkno, reln->rd_node.spcNode,
-				 reln->rd_node.dbNode, reln->rd_node.relNode);
+		{
+			UnlockReleaseBuffer(buffer);
+			log_invalid_page(reln->rd_node, blkno, true);
+			return InvalidBuffer;
+		}
 	}
 
 	return buffer;
@@ -195,6 +367,7 @@ void
 XLogInitRelationCache(void)
 {
 	_xl_init_rel_cache();
+	invalid_page_tab = NULL;
 }
 
 void
@@ -300,22 +473,26 @@ XLogOpenRelation(RelFileNode rnode)
  *
  * Currently, we don't bother to physically remove the relation from the
  * cache, we just let it age out normally.
+ *
+ * This also takes care of removing any open "invalid-page" records for
+ * the relation.
  */
 void
 XLogDropRelation(RelFileNode rnode)
 {
-	XLogRelDesc *rdesc;
 	XLogRelCacheEntry *hentry;
 
 	hentry = (XLogRelCacheEntry *)
 		hash_search(_xlrelcache, (void *) &rnode, HASH_FIND, NULL);
 
-	if (!hentry)
-		return;					/* not in cache so no work */
+	if (hentry)
+	{
+		XLogRelDesc *rdesc = hentry->rdesc;
 
-	rdesc = hentry->rdesc;
+		RelationCloseSmgr(&(rdesc->reldata));
+	}
 
-	RelationCloseSmgr(&(rdesc->reldata));
+	forget_invalid_pages(rnode, 0);
 }
 
 /*
@@ -338,4 +515,18 @@ XLogDropDatabase(Oid dbid)
 		if (hentry->rnode.dbNode == dbid)
 			RelationCloseSmgr(&(rdesc->reldata));
 	}
+
+	forget_invalid_pages_db(dbid);
+}
+
+/*
+ * Truncate a relation during XLOG replay
+ *
+ * We don't need to do anything to the fake relcache, but we do need to
+ * clean up any open "invalid-page" records for the dropped pages.
+ */
+void
+XLogTruncateRelation(RelFileNode rnode, BlockNumber nblocks)
+{
+	forget_invalid_pages(rnode, nblocks);
 }

src/backend/storage/smgr/smgr.c

@@ -11,13 +11,14 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.98 2006/03/30 22:11:55 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.99 2006/04/14 20:27:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
 #include "access/xact.h"
+#include "access/xlogutils.h"
 #include "commands/tablespace.h"
 #include "pgstat.h"
 #include "storage/bufmgr.h"
@@ -942,6 +943,9 @@ smgr_redo(XLogRecPtr lsn, XLogRecord *record)
 					 reln->smgr_rnode.dbNode,
 					 reln->smgr_rnode.relNode,
 					 xlrec->blkno)));
+
+		/* Also tell xlogutils.c about it */
+		XLogTruncateRelation(xlrec->rnode, xlrec->blkno);
 	}
 	else
 		elog(PANIC, "smgr_redo: unknown op code %u", info);

src/include/access/xlogutils.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/xlogutils.h,v 1.20 2006/03/29 21:17:39 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/xlogutils.h,v 1.21 2006/04/14 20:27:24 tgl Exp $
  */
 #ifndef XLOG_UTILS_H
 #define XLOG_UTILS_H
@@ -16,11 +16,13 @@
 
 
 extern void XLogInitRelationCache(void);
+extern void XLogCheckInvalidPages(void);
 extern void XLogCloseRelationCache(void);
 
 extern Relation XLogOpenRelation(RelFileNode rnode);
 extern void XLogDropRelation(RelFileNode rnode);
 extern void XLogDropDatabase(Oid dbid);
+extern void XLogTruncateRelation(RelFileNode rnode, BlockNumber nblocks);
 
 extern Buffer XLogReadBuffer(Relation reln, BlockNumber blkno, bool init);