Solve the problem of OID collisions by probing for duplicate OIDs

whenever we generate a new OID.  This prevents occasional duplicate-OID
errors that can otherwise occur once the OID counter has wrapped around.
Duplicate relfilenode values are also checked for when creating new
physical files.  Per my recent proposal.

src/backend/commands/dbcommands.c

@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.169 2005/08/02 19:02:31 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.170 2005/08/12 01:35:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -80,7 +80,7 @@ createdb(const CreatedbStmt *stmt)
 	TransactionId src_frozenxid;
 	Oid			src_deftablespace;
 	volatile Oid dst_deftablespace;
-	volatile Relation pg_database_rel = NULL;
+	volatile Relation pg_database_rel;
 	HeapTuple	tuple;
 	TupleDesc	pg_database_dsc;
 	Datum		new_record[Natts_pg_database];
@@ -347,9 +347,13 @@ createdb(const CreatedbStmt *stmt)
 
 	/*
 	 * Preassign OID for pg_database tuple, so that we can compute db
-	 * path.
+	 * path.  We have to open pg_database to do this, but we don't want
+	 * to take ExclusiveLock yet, so just do it and close again.
 	 */
-	dboid = newoid();
+	pg_database_rel = heap_open(DatabaseRelationId, AccessShareLock);
+	dboid = GetNewOid(pg_database_rel);
+	heap_close(pg_database_rel, AccessShareLock);
+	pg_database_rel = NULL;
 
 	/*
 	 * Force dirty buffers out to disk, to ensure source database is

src/backend/commands/trigger.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.190 2005/08/01 20:31:07 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.191 2005/08/12 01:35:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -184,7 +184,9 @@ CreateTrigger(CreateTrigStmt *stmt, bool forConstraint)
 	 * Generate the trigger's OID now, so that we can use it in the name
 	 * if needed.
 	 */
-	trigoid = newoid();
+	tgrel = heap_open(TriggerRelationId, RowExclusiveLock);
+
+	trigoid = GetNewOid(tgrel);
 
 	/*
 	 * If trigger is an RI constraint, use specified trigger name as
@@ -252,7 +254,6 @@ CreateTrigger(CreateTrigStmt *stmt, bool forConstraint)
 	 * NOTE that this is cool only because we have AccessExclusiveLock on the
 	 * relation, so the trigger set won't be changing underneath us.
 	 */
-	tgrel = heap_open(TriggerRelationId, RowExclusiveLock);
 	ScanKeyInit(&key,
 				Anum_pg_trigger_tgrelid,
 				BTEqualStrategyNumber, F_OIDEQ,

src/backend/commands/typecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/typecmds.c,v 1.78 2005/08/04 01:09:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/typecmds.c,v 1.79 2005/08/12 01:35:58 tgl Exp $
  *
  * DESCRIPTION
  *	  The "DefineFoo" routines take the parse tree and pick out the
@@ -339,7 +339,6 @@ DefineType(List *names, List *parameters)
 	typoid =
 		TypeCreate(typeName,	/* type name */
 				   typeNamespace,		/* namespace */
-				   InvalidOid,	/* preassigned type oid (not done here) */
 				   InvalidOid,	/* relation oid (n/a here) */
 				   0,			/* relation kind (ditto) */
 				   internalLength,		/* internal size */
@@ -372,7 +371,6 @@ DefineType(List *names, List *parameters)
 
 	TypeCreate(shadow_type,		/* type name */
 			   typeNamespace,	/* namespace */
-			   InvalidOid,		/* preassigned type oid (not done here) */
 			   InvalidOid,		/* relation oid (n/a here) */
 			   0,				/* relation kind (ditto) */
 			   -1,				/* internal size */
@@ -724,7 +722,6 @@ DefineDomain(CreateDomainStmt *stmt)
 	domainoid =
 		TypeCreate(domainName,	/* type name */
 				   domainNamespace,		/* namespace */
-				   InvalidOid,	/* preassigned type oid (none here) */
 				   InvalidOid,	/* relation oid (n/a here) */
 				   0,			/* relation kind (ditto) */
 				   internalLength,		/* internal size */