When a relation is moved to another tablespace, we can't assume that we can

use the old relfilenode in the new tablespace. There might be another relation
in the new tablespace with the same relfilenode, so we must generate a fresh
relfilenode in the new tablespace.

The 8.3 patch to let deleted relation files linger as zero-length files until
the next checkpoint made this more obvious: moving a relation from one table
space another, and then back again, caused a collision with the lingering
file.

Back-patch to 8.1. The issue is present in 8.0 as well, but it doesn't seem
worth fixing there, because we didn't have protection from OID collisions
after OID wraparound before 8.1.

Report by Guillaume Lelarge.

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.242.2.3 2008/05/19 04:14:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.242.2.4 2008/10/07 11:15:48 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -5830,6 +5830,7 @@ ATExecSetTableSpace(Oid tableOid, Oid newTableSpace)
 	Oid			oldTableSpace;
 	Oid			reltoastrelid;
 	Oid			reltoastidxid;
+	Oid			newrelfilenode;
 	RelFileNode newrnode;
 	SMgrRelation dstrel;
 	Relation	pg_class;
@@ -5890,9 +5891,18 @@ ATExecSetTableSpace(Oid tableOid, Oid newTableSpace)
 		elog(ERROR, "cache lookup failed for relation %u", tableOid);
 	rd_rel = (Form_pg_class) GETSTRUCT(tuple);
 
+	/*
+	 * Relfilenodes are not unique across tablespaces, so we need to allocate
+	 * a new one in the new tablespace.
+	 */
+	newrelfilenode = GetNewRelFileNode(newTableSpace,
+									   rel->rd_rel->relisshared,
+									   NULL);
+
 	/* create another storage file. Is it a little ugly ? */
 	/* NOTE: any conflict in relfilenode value will be caught here */
 	newrnode = rel->rd_node;
+	newrnode.relNode = newrelfilenode;
 	newrnode.spcNode = newTableSpace;
 
 	dstrel = smgropen(newrnode);
@@ -5913,6 +5923,7 @@ ATExecSetTableSpace(Oid tableOid, Oid newTableSpace)
 
 	/* update the pg_class row */
 	rd_rel->reltablespace = (newTableSpace == MyDatabaseTableSpace) ? InvalidOid : newTableSpace;
+	rd_rel->relfilenode = newrelfilenode;
 	simple_heap_update(pg_class, &tuple->t_self, tuple);
 	CatalogUpdateIndexes(pg_class, tuple);