Free space in temp tablespace

Question

SQL> show parameter block
NAME                                 TYPE        VALUE
db_block_buffers                     integer     0
db_block_checking                    boolean     FALSE
db_block_checksum                    boolean     TRUE
db_block_size                        integer     8192
db_file_multiblock_read_count        integer     8
SQL> SELECT tablespace_name,
       total_blocks,
       used_blocks,
       free_blocks,
    (total_blocks*8)/1024 as total_MB,
    (used_blocks*8)/1024  as used_MB,
    (free_blocks*8)/1024  as free_MB
FROM   v$sort_segment;
   2    3    4    5    6    7    8 
TABLESPACE_NAME                 TOTAL_BLOCKS USED_BLOCKS FREE_BLOCKS   TOTAL_MB    USED_MB    FREE_MB
TEMP                                   72704        2944       69760        568         23        545
SQL>  select (sum(bytes_free)/1024/1024) Size_MB from v$temp_space_header
order by file_id  2 
  3  /
   SIZE_MB
      1479
SQL>
My version is 9.2.0.7
why temp free space is different in both queries above..
which one is correct.....

Answer 1

why temp free space is different in both queries above..Because you are looking at two different values.
V$SORT_SEGMENT gives details about the sort segment created in a temporary tablespace. The sort segment created may or may not be of the same size as the complete temporary tablespace. In your case, the sort segment has a total size of 568 MB but only 23 MB is being used.
V$TEMP_SPACE_HEADER refers to the physical files allocated to the temporary tablespace; so the other query is giving you the free bytes in those files.