peformance issue - nls_lang

set NLS_LANG=american_america.utf8
--
19:54:07 SQL> select * from character_set;

171080 rows selected.

Elapsed: 00:00:29.68

Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
3808 consistent gets
2009 physical reads
0 redo size
16942067 bytes sent via SQL*Net to client
1026 bytes received via SQL*Net from client
59 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
171080 rows processed
--
set NLS_LANG=
--
SQL> select * from character_set;

171080 rows selected.

Elapsed: 00:00:02.26

Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
14909 consistent gets
2855 physical reads
0 redo size
18383263 bytes sent via SQL*Net to client
125854 bytes received via SQL*Net from client
11407 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
171080 rows processed