During recovery, if we reach consistent state and still have entries in the

invalid-page hash table, PANIC immediately. Immediate PANIC is much better
than waiting for end-of-recovery, which is what we did before, because the
end-of-recovery might not come until months later if this is a standby
server.

Also refrain from creating a restartpoint if there are invalid-page entries
in the hash table. Restarting recovery from such a restartpoint would not
see the invalid references, and wouldn't be able to cross-check them when
consistency is reached. That wouldn't matter when things are going smoothly,
but the more sanity checks you have the better.

Fujii Masao

src/backend/access/transam/xlog.c

@@ -562,7 +562,7 @@ static TimeLineID lastPageTLI = 0;
 static XLogRecPtr minRecoveryPoint;		/* local copy of
 										 * ControlFile->minRecoveryPoint */
 static bool updateMinRecoveryPoint = true;
-static bool reachedMinRecoveryPoint = false;
+bool reachedMinRecoveryPoint = false;
 
 static bool InRedo = false;
 
@@ -6758,12 +6758,6 @@ StartupXLOG(void)
 		/* Disallow XLogInsert again */
 		LocalXLogInsertAllowed = -1;
 
-		/*
-		 * Check to see if the XLOG sequence contained any unresolved
-		 * references to uninitialized pages.
-		 */
-		XLogCheckInvalidPages();
-
 		/*
 		 * Perform a checkpoint to update all our recovery activity to disk.
 		 *
@@ -6906,6 +6900,12 @@ CheckRecoveryConsistency(void)
 		XLByteLE(minRecoveryPoint, EndRecPtr) &&
 		XLogRecPtrIsInvalid(ControlFile->backupStartPoint))
 	{
+		/*
+		 * Check to see if the XLOG sequence contained any unresolved
+		 * references to uninitialized pages.
+		 */
+		XLogCheckInvalidPages();
+
 		reachedMinRecoveryPoint = true;
 		ereport(LOG,
 				(errmsg("consistent recovery state reached at %X/%X",
@@ -7907,7 +7907,7 @@ RecoveryRestartPoint(const CheckPoint *checkPoint)
 	volatile XLogCtlData *xlogctl = XLogCtl;
 
 	/*
-	 * Is it safe to checkpoint?  We must ask each of the resource managers
+	 * Is it safe to restartpoint?  We must ask each of the resource managers
 	 * whether they have any partial state information that might prevent a
 	 * correct restart from this point.  If so, we skip this opportunity, but
 	 * return at the next checkpoint record for another try.
@@ -7926,6 +7926,22 @@ RecoveryRestartPoint(const CheckPoint *checkPoint)
 			}
 	}
 
+	/*
+	 * Also refrain from creating a restartpoint if we have seen any references
+	 * to non-existent pages. Restarting recovery from the restartpoint would
+	 * not see the references, so we would lose the cross-check that the pages
+	 * belonged to a relation that was dropped later.
+	 */
+	if (XLogHaveInvalidPages())
+	{
+		elog(trace_recovery(DEBUG2),
+			 "could not record restart point at %X/%X because there "
+			 "are unresolved references to invalid pages",
+			 checkPoint->redo.xlogid,
+			 checkPoint->redo.xrecoff);
+		return;
+	}
+
 	/*
 	 * Copy the checkpoint record to shared memory, so that checkpointer
 	 * can work out the next time it wants to perform a restartpoint.

src/backend/access/transam/xlogutils.c

@@ -52,6 +52,22 @@ typedef struct xl_invalid_page
 static HTAB *invalid_page_tab = NULL;
 
 
+/* Report a reference to an invalid page */
+static void
+report_invalid_page(int elevel, RelFileNode node, ForkNumber forkno,
+					BlockNumber blkno, bool present)
+{
+	char	   *path = relpathperm(node, forkno);
+
+	if (present)
+		elog(elevel, "page %u of relation %s is uninitialized",
+			 blkno, path);
+	else
+		elog(elevel, "page %u of relation %s does not exist",
+			 blkno, path);
+	pfree(path);
+}
+
 /* Log a reference to an invalid page */
 static void
 log_invalid_page(RelFileNode node, ForkNumber forkno, BlockNumber blkno,
@@ -61,23 +77,27 @@ log_invalid_page(RelFileNode node, ForkNumber forkno, BlockNumber blkno,
 	xl_invalid_page *hentry;
 	bool		found;
 
+	/*
+	 * Once recovery has reached a consistent state, the invalid-page table
+	 * should be empty and remain so. If a reference to an invalid page is
+	 * found after consistency is reached, PANIC immediately. This might
+	 * seem aggressive, but it's better than letting the invalid reference
+	 * linger in the hash table until the end of recovery and PANIC there,
+	 * which might come only much later if this is a standby server.
+	 */
+	if (reachedMinRecoveryPoint)
+	{
+		report_invalid_page(WARNING, node, forkno, blkno, present);
+		elog(PANIC, "WAL contains references to invalid pages");
+	}
+
 	/*
 	 * 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 (log_min_messages <= DEBUG1 || client_min_messages <= DEBUG1)
-	{
-		char	   *path = relpathperm(node, forkno);
-
-		if (present)
-			elog(DEBUG1, "page %u of relation %s is uninitialized",
-				 blkno, path);
-		else
-			elog(DEBUG1, "page %u of relation %s does not exist",
-				 blkno, path);
-		pfree(path);
-	}
+		report_invalid_page(DEBUG1, node, forkno, blkno, present);
 
 	if (invalid_page_tab == NULL)
 	{
@@ -181,6 +201,16 @@ forget_invalid_pages_db(Oid dbid)
 	}
 }
 
+/* Are there any unresolved references to invalid pages? */
+bool
+XLogHaveInvalidPages(void)
+{
+	if (invalid_page_tab != NULL &&
+		hash_get_num_entries(invalid_page_tab) > 0)
+		return true;
+	return false;
+}
+
 /* Complain about any remaining invalid-page entries */
 void
 XLogCheckInvalidPages(void)
@@ -200,15 +230,8 @@ XLogCheckInvalidPages(void)
 	 */
 	while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL)
 	{
-		char	   *path = relpathperm(hentry->key.node, hentry->key.forkno);
-
-		if (hentry->present)
-			elog(WARNING, "page %u of relation %s was uninitialized",
-				 hentry->key.blkno, path);
-		else
-			elog(WARNING, "page %u of relation %s did not exist",
-				 hentry->key.blkno, path);
-		pfree(path);
+		report_invalid_page(WARNING, hentry->key.node, hentry->key.forkno,
+							hentry->key.blkno, hentry->present);
 		foundone = true;
 	}
 

src/include/access/xlog.h

@@ -190,6 +190,8 @@ typedef enum
 
 extern XLogRecPtr XactLastRecEnd;
 
+extern bool reachedMinRecoveryPoint;
+
 /* these variables are GUC parameters related to XLOG */
 extern int	CheckPointSegments;
 extern int	wal_keep_segments;

src/include/access/xlogutils.h

@@ -14,6 +14,7 @@
 #include "storage/bufmgr.h"
 
 
+extern bool XLogHaveInvalidPages(void);
 extern void XLogCheckInvalidPages(void);
 
 extern void XLogDropRelation(RelFileNode rnode, ForkNumber forknum);