0008-wal_decoding-Introduce-InvalidCommandId-and-declare-.patch

>From 321a38776fcd10df090f737b722a692b649f969c Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Tue, 13 Nov 2012 12:18:07 +0100
Subject: [PATCH 08/19] wal_decoding: Introduce InvalidCommandId and declare
 that to be the new maximum for
 CommandCounterIncrement

This is useful to be able to represent a CommandId thats invalid. There was no
such value before.

This decreases the possible number of subtransactions by one which seems
unproblematic. Its also not a problem for pg_upgrade because cmin/cmax are
never looked at outside the context of their own transaction (spare timetravel
access, but thats new anyway).
---
 src/backend/access/transam/xact.c | 4 ++--
 src/include/c.h                   | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 81d2687..369d2b6 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -745,12 +745,12 @@ CommandCounterIncrement(void)
 	if (currentCommandIdUsed)
 	{
 		currentCommandId += 1;
-		if (currentCommandId == FirstCommandId) /* check for overflow */
+		if (currentCommandId == InvalidCommandId)
 		{
 			currentCommandId -= 1;
 			ereport(ERROR,
 					(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-					 errmsg("cannot have more than 2^32-1 commands in a transaction")));
+					 errmsg("cannot have more than 2^32-2 commands in a transaction")));
 		}
 		currentCommandIdUsed = false;
 
diff --git a/src/include/c.h b/src/include/c.h
index 57664e8..aba0049 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -367,6 +367,7 @@ typedef uint32 MultiXactOffset;
 typedef uint32 CommandId;
 
 #define FirstCommandId	((CommandId) 0)
+#define InvalidCommandId	(~(CommandId)0)
 
 /*
  * Array indexing support
-- 
1.7.12.289.g0ce9864.dirty