Introduce InvalidCommandId.

robertmhaas · robertmhaas · commit 71901ab6daaa · 2013-09-09T16:25:29.000-04:00
This allows a 32-bit field to represent an *optional* command ID
without a separate flag bit.

Andres Freund
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
@@ -766,12 +766,12 @@ 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
@@ -368,6 +368,7 @@ typedef uint32 MultiXactOffset;
 typedef uint32 CommandId;
 
 #define FirstCommandId	((CommandId) 0)
+#define InvalidCommandId	(~(CommandId)0)
 
 /*
  * Array indexing support

Original file line number	Diff line number	Diff line change
`@@ -766,12 +766,12 @@ CommandCounterIncrement(void)`
`766`	`766`	`if (currentCommandIdUsed)`
`767`	`767`	`{`
`768`	`768`	`currentCommandId += 1;`
`769`		`- if (currentCommandId == FirstCommandId) /* check for overflow */`
	`769`	`+ if (currentCommandId == InvalidCommandId)`
`770`	`770`	`{`
`771`	`771`	`currentCommandId -= 1;`
`772`	`772`	`ereport(ERROR,`
`773`	`773`	`(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),`
`774`		`- errmsg("cannot have more than 2^32-1 commands in a transaction")));`
	`774`	`+ errmsg("cannot have more than 2^32-2 commands in a transaction")));`
`775`	`775`	`}`
`776`	`776`	`currentCommandIdUsed = false;`
`777`	`777`