Repair two problems with WAL logging of sequence nextvalI() ops, as

per recent pghackers discussion: force a new WAL record at first nextval
after a checkpoint, and ensure that xlog is flushed to disk if a nextval
record is the only thing emitted by a transaction.

1 files changed, 47 insertions, 29 deletions

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index a9bba59d378..b3d51a49ec1 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.115 2001/11/01 06:17:01 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.115.2.1 2002/03/15 19:20:43 tgl Exp $
  *
  * NOTES
  *		Transaction aborts can now occur two ways:
@@ -546,32 +546,48 @@ RecordTransactionCommit(void)
 	xid = GetCurrentTransactionId();
 
 	/*
-	 * We needn't write anything in xlog or clog if the transaction was
-	 * read-only, which we check by testing if it made any xlog entries.
+	 * We only need to log the commit in xlog and clog if the transaction made
+	 * any transaction-controlled XLOG entries.  (Otherwise, its XID appears
+	 * nowhere in permanent storage, so no one will ever care if it
+	 * committed.)  However, we must flush XLOG to disk if we made any XLOG
+	 * entries, whether in or out of transaction control.  For example, if we
+	 * reported a nextval() result to the client, this ensures that any XLOG
+	 * record generated by nextval will hit the disk before we report the
+	 * transaction committed.
 	 */
-	if (MyLastRecPtr.xrecoff != 0)
+	if (MyXactMadeXLogEntry)
 	{
-		XLogRecData rdata;
-		xl_xact_commit xlrec;
 		XLogRecPtr	recptr;
 
 		BufmgrCommit();
 
-		xlrec.xtime = time(NULL);
-		rdata.buffer = InvalidBuffer;
-		rdata.data = (char *) (&xlrec);
-		rdata.len = SizeOfXactCommit;
-		rdata.next = NULL;
-
 		START_CRIT_SECTION();
 
-		/*
-		 * SHOULD SAVE ARRAY OF RELFILENODE-s TO DROP
-		 */
-		recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT, &rdata);
+		if (MyLastRecPtr.xrecoff != 0)
+		{
+			/* Need to emit a commit record */
+			XLogRecData rdata;
+			xl_xact_commit xlrec;
+
+			xlrec.xtime = time(NULL);
+			rdata.buffer = InvalidBuffer;
+			rdata.data = (char *) (&xlrec);
+			rdata.len = SizeOfXactCommit;
+			rdata.next = NULL;
+
+			/*
+			 * XXX SHOULD SAVE ARRAY OF RELFILENODE-s TO DROP
+			 */
+			recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_COMMIT, &rdata);
+		}
+		else
+		{
+			/* Just flush through last record written by me */
+			recptr = ProcLastRecEnd;
+		}
 
 		/*
-		 * Sleep before commit! So we can flush more than one commit
+		 * Sleep before flush! So we can flush more than one commit
 		 * records per single fsync.  (The idea is some other backend may
 		 * do the XLogFlush while we're sleeping.  This needs work still,
 		 * because on most Unixen, the minimum select() delay is 10msec or
@@ -593,15 +609,17 @@ RecordTransactionCommit(void)
 
 		XLogFlush(recptr);
 
-		/* Break the chain of back-links in the XLOG records I output */
-		MyLastRecPtr.xrecoff = 0;
-
-		/* Mark the transaction committed in clog */
-		TransactionIdCommit(xid);
+		/* Mark the transaction committed in clog, if needed */
+		if (MyLastRecPtr.xrecoff != 0)
+			TransactionIdCommit(xid);
 
 		END_CRIT_SECTION();
 	}
 
+	/* Break the chain of back-links in the XLOG records I output */
+	MyLastRecPtr.xrecoff = 0;
+	MyXactMadeXLogEntry = false;
+
 	/* Show myself as out of the transaction in PROC array */
 	MyProc->logRec.xrecoff = 0;
 
@@ -689,8 +707,11 @@ RecordTransactionAbort(void)
 	TransactionId xid = GetCurrentTransactionId();
 
 	/*
-	 * We needn't write anything in xlog or clog if the transaction was
-	 * read-only, which we check by testing if it made any xlog entries.
+	 * We only need to log the abort in xlog and clog if the transaction made
+	 * any transaction-controlled XLOG entries.  (Otherwise, its XID appears
+	 * nowhere in permanent storage, so no one will ever care if it
+	 * committed.)  We do not flush XLOG to disk in any case, since the
+	 * default assumption after a crash would be that we aborted, anyway.
 	 *
 	 * Extra check here is to catch case that we aborted partway through
 	 * RecordTransactionCommit ...
@@ -714,11 +735,6 @@ RecordTransactionAbort(void)
 		 */
 		recptr = XLogInsert(RM_XACT_ID, XLOG_XACT_ABORT, &rdata);
 
-		/*
-		 * There's no need for XLogFlush here, since the default
-		 * assumption would be that we aborted, anyway.
-		 */
-
 		/* Mark the transaction aborted in clog */
 		TransactionIdAbort(xid);
 
@@ -727,6 +743,8 @@ RecordTransactionAbort(void)
 
 	/* Break the chain of back-links in the XLOG records I output */
 	MyLastRecPtr.xrecoff = 0;
+	MyXactMadeXLogEntry = false;
+
 	/* Show myself as out of the transaction in PROC array */
 	MyProc->logRec.xrecoff = 0;