Write a WAL record whenever we perform an operation without WAL-logging

that would've been WAL-logged if archiving was enabled. If we encounter
such records in archive recovery anyway, we know that some data is
missing from the log. A WARNING is emitted in that case.

Original patch by Fujii Masao, with changes by me.

src/backend/access/heap/heapam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.282 2010/01/14 11:08:00 sriggs Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.283 2010/01/20 19:43:40 heikki Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -5074,10 +5074,16 @@ heap2_desc(StringInfo buf, uint8 xl_info, char *rec)
 void
 heap_sync(Relation rel)
 {
+	char reason[NAMEDATALEN + 30];
+
 	/* temp tables never need fsync */
 	if (rel->rd_istemp)
 		return;
 
+	snprintf(reason, sizeof(reason), "heap inserts on \"%s\"",
+			 RelationGetRelationName(rel));
+	XLogReportUnloggedStatement(reason);
+
 	/* main heap */
 	FlushRelationBuffers(rel);
 	/* FlushRelationBuffers will have opened rd_smgr */

src/backend/access/nbtree/nbtsort.c

@@ -59,7 +59,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsort.c,v 1.122 2010/01/15 09:19:00 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsort.c,v 1.123 2010/01/20 19:43:40 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -215,6 +215,18 @@ _bt_leafbuild(BTSpool *btspool, BTSpool *btspool2)
 	 */
 	wstate.btws_use_wal = XLogIsNeeded() && !wstate.index->rd_istemp;
 
+	/*
+	 * Write an XLOG UNLOGGED record if WAL-logging was skipped because
+	 * WAL archiving is not enabled.
+	 */
+	if (!wstate.btws_use_wal && !wstate.index->rd_istemp)
+	{
+		char reason[NAMEDATALEN + 20];
+		snprintf(reason, sizeof(reason), "b-tree build on \"%s\"",
+				 RelationGetRelationName(wstate.index));
+		XLogReportUnloggedStatement(reason);
+	}
+
 	/* reserve the metapage */
 	wstate.btws_pages_alloced = BTREE_METAPAGE + 1;
 	wstate.btws_pages_written = 0;

src/backend/access/transam/xlog.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.358 2010/01/15 09:19:00 heikki Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.359 2010/01/20 19:43:40 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -7561,6 +7561,31 @@ RequestXLogSwitch(void)
 	return RecPtr;
 }
 
+/*
+ * Write an XLOG UNLOGGED record, indicating that some operation was
+ * performed on data that we fsync()'d directly to disk, skipping
+ * WAL-logging.
+ *
+ * Such operations screw up archive recovery, so we complain if we see
+ * these records during archive recovery. That shouldn't happen in a
+ * correctly configured server, but you can induce it by temporarily
+ * disabling archiving and restarting, so it's good to at least get a
+ * warning of silent data loss in such cases. These records serve no
+ * other purpose and are simply ignored during crash recovery.
+ */
+void
+XLogReportUnloggedStatement(char *reason)
+{
+	XLogRecData rdata;
+
+	rdata.buffer = InvalidBuffer;
+	rdata.data = reason;
+	rdata.len = strlen(reason) + 1;
+	rdata.next = NULL;
+
+	XLogInsert(RM_XLOG_ID, XLOG_UNLOGGED, &rdata);
+}
+
 /*
  * XLOG resource manager's routines
  *
@@ -7703,6 +7728,19 @@ xlog_redo(XLogRecPtr lsn, XLogRecord *record)
 			LWLockRelease(ControlFileLock);
 		}
 	}
+	else if (info == XLOG_UNLOGGED)
+	{
+		if (InArchiveRecovery)
+		{
+			/*
+			 * Note: We don't print the reason string from the record,
+			 * because that gets added as a line using xlog_desc()
+			 */
+			ereport(WARNING,
+					(errmsg("unlogged operation performed, data may be missing"),
+					 errhint("This can happen if you temporarily disable archive_mode without taking a new base backup.")));
+		}
+	}
 }
 
 void
@@ -7752,6 +7790,12 @@ xlog_desc(StringInfo buf, uint8 xl_info, char *rec)
 		appendStringInfo(buf, "backup end: %X/%X",
 						 startpoint.xlogid, startpoint.xrecoff);
 	}
+	else if (info == XLOG_UNLOGGED)
+	{
+		char *reason = rec;
+
+		appendStringInfo(buf, "unlogged operation: %s", reason);
+	}
 	else
 		appendStringInfo(buf, "UNKNOWN");
 }

src/backend/commands/cluster.c

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.193 2010/01/15 09:19:01 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.194 2010/01/20 19:43:40 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -821,6 +821,18 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex,
 	 */
 	use_wal = XLogIsNeeded() && !NewHeap->rd_istemp;
 
+	/*
+	 * Write an XLOG UNLOGGED record if WAL-logging was skipped because
+	 * WAL archiving is not enabled.
+	 */
+	if (!use_wal && !NewHeap->rd_istemp)
+	{
+		char reason[NAMEDATALEN + 20];
+		snprintf(reason, sizeof(reason), "CLUSTER on \"%s\"",
+				 RelationGetRelationName(NewHeap));
+		XLogReportUnloggedStatement(reason);
+	}
+
 	/* use_wal off requires rd_targblock be initially invalid */
 	Assert(NewHeap->rd_targblock == InvalidBlockNumber);
 

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.316 2010/01/17 22:56:21 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.317 2010/01/20 19:43:40 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -7015,6 +7015,19 @@ ATExecSetTableSpace(Oid tableOid, Oid newTableSpace)
 
 	heap_close(pg_class, RowExclusiveLock);
 
+	/*
+	 * Write an XLOG UNLOGGED record if WAL-logging was skipped because
+	 * WAL archiving is not enabled.
+	 */
+	if (!XLogIsNeeded() && !rel->rd_istemp)
+	{
+		char reason[NAMEDATALEN + 40];
+		snprintf(reason, sizeof(reason), "ALTER TABLE SET TABLESPACE on \"%s\"",
+				 RelationGetRelationName(rel));
+
+		XLogReportUnloggedStatement(reason);
+	}
+
 	relation_close(rel, NoLock);
 
 	/* Make sure the reltablespace change is visible */
@@ -7043,6 +7056,10 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
 	/*
 	 * We need to log the copied data in WAL iff WAL archiving/streaming is
 	 * enabled AND it's not a temp rel.
+	 *
+	 * Note: If you change the conditions here, update the conditions in
+	 * ATExecSetTableSpace() for when an XLOG UNLOGGED record is written
+	 * to match.
 	 */
 	use_wal = XLogIsNeeded() && !istemp;
 

src/include/access/xlog.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.97 2010/01/16 00:04:41 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.98 2010/01/20 19:43:40 heikki Exp $
  */
 #ifndef XLOG_H
 #define XLOG_H
@@ -278,6 +278,7 @@ extern void InitXLOGAccess(void);
 extern void CreateCheckPoint(int flags);
 extern bool CreateRestartPoint(int flags);
 extern void XLogPutNextOid(Oid nextOid);
+extern void XLogReportUnloggedStatement(char *reason);
 extern XLogRecPtr GetRedoRecPtr(void);
 extern XLogRecPtr GetInsertRecPtr(void);
 extern XLogRecPtr GetWriteRecPtr(void);

src/include/catalog/pg_control.h

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_control.h,v 1.48 2010/01/04 12:50:50 heikki Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_control.h,v 1.49 2010/01/20 19:43:40 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -63,6 +63,7 @@ typedef struct CheckPoint
 #define XLOG_NEXTOID					0x30
 #define XLOG_SWITCH						0x40
 #define XLOG_BACKUP_END					0x50
+#define XLOG_UNLOGGED					0x60
 
 
 /* System status indicator */