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Temporary Tablespaces in ORACLE

Temporary Tablespaces

Temporary tablespaces are used for special operations, particularly for sorting data results on disk and for hash joins in SQL. For SQL with millions of rows returned, the sort operation is too large for the RAM area and must occur on disk. The temporary tablespace is where this takes place.

Each database should have one temporary tablespace that is created when the database is created. You create, drop and manage tablespaces with create temporary tablespace, drop temporary tablespace and alter temporary tablespace commands, each of which is like it?s create tablespace counterpart.
The only other difference is that a temporary tablespace uses temporary files (also called tempfiles) rather than regular datafiles. Thus, instead of using the datafiles keyword you use the tempfiles keyword when issuing a create, drop or alter tablespace command as you can see in these examples:

 CREATE TEMPORARY TABLESPACE temp
TEMPFILE ?/ora01/oracle/oradata/booktst_temp_01.dbf? SIZE 50m;
DROP TEMPORARY TABLESPACE temp INCLUDING CONTENTS AND DATAFILES;

Tempfiles are a bit different than datafiles in that you may not immediately see them grow to the size that they have been allocated (this particular functionality is platform dependent). Hence, don?t panic if you see a file that looks too small.

col allocated_bytes format 999,999,999,999,999

col free_bytes format 999,999,999,999,999

 select
a.tablespace_name,
a.file_name,
a.bytes c3,
b.free_bytes
FROM
dba_temp_files a,
(SELECT file_id, SUM(bytes) free_bytes
FROM dba_free_space b GROUP BY file_id) b
WHERE
a.file_id=b.file_id
ORDER BY
a.tablespace_name;
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