Avoid incrementing the CommandCounter when CommandCounterIncrement is called

but no database changes have been made since the last CommandCounterIncrement.
This should result in a significant improvement in the number of "commands"
that can typically be performed within a transaction before hitting the 2^32
CommandId size limit.  In particular this buys back (and more) the possible
adverse consequences of my previous patch to fix plan caching behavior.

The implementation requires tracking whether the current CommandCounter
value has been "used" to mark any tuples.  CommandCounter values stored into
snapshots are presumed not to be used for this purpose.  This requires some
small executor changes, since the executor used to conflate the curcid of
the snapshot it was using with the command ID to mark output tuples with.
Separating these concepts allows some small simplifications in executor APIs.

Something for the TODO list: look into having CommandCounterIncrement not do
AcceptInvalidationMessages.  It seems fairly bogus to be doing it there,
but exactly where to do it instead isn't clear, and I'm disinclined to mess
with asynchronous behavior during late beta.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index ef7e04ca28..c68d828fea 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/copy.c,v 1.288 2007/11/15 21:14:33 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/copy.c,v 1.289 2007/11/30 21:22:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1033,7 +1033,7 @@ DoCopy(const CopyStmt *stmt, const char *queryString)
 		 * which COPY can be invoked, I think it's OK, because the active
 		 * snapshot shouldn't be shared with anything else anyway.)
 		 */
-		ActiveSnapshot->curcid = GetCurrentCommandId();
+		ActiveSnapshot->curcid = GetCurrentCommandId(false);
 
 		/* Create dest receiver for COPY OUT */
 		dest = CreateDestReceiver(DestCopyOut, NULL);
@@ -1637,7 +1637,7 @@ CopyFrom(CopyState cstate)
 	ExprContext *econtext;		/* used for ExecEvalExpr for default atts */
 	MemoryContext oldcontext = CurrentMemoryContext;
 	ErrorContextCallback errcontext;
-	CommandId	mycid = GetCurrentCommandId();
+	CommandId	mycid = GetCurrentCommandId(true);
 	bool		use_wal = true; /* by default, use WAL logging */
 	bool		use_fsm = true; /* by default, use FSM for free space */