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How To Free Temporary Segment in Temporary Tablespace Dynamically

Purpose

-------

The purpose of this article is to advise on how to free the sort segment in a

temporary tablespace of type TEMPORARY.

Scope & Application

-------------------

DBAs

How to free a sort segment

--------------------------

You want to liberate the sort segment created in its current temporary

tablespace of type TEMPORARY.  The storage clause associated with this segment

is not correct and you must change it.  But, as explained in [NOTE:102339.1],

the sort segment is only freed by smon on startup of the instance.

Sometimes it will be interesting to change the storage clause of the sort

segment without shutting down the database.  Particularly when these storage

clauses are too small, it will be interesting to increase it, to avoid

splitting of the temporary segment on too many extents.

Too many extents on a temporary segment may lead to spinning of smon on the

next startup of the database.  Please note that this extent maintenance will

take place immediately after you have freed them.

Answer

------

If you consider a sort segment which is already created on the current

temporary TEMP segment.

SQL> select tablespace_name, CURRENT_USERS, TOTAL_BLOCKS, USED_BLOCKS, FREE_BLOCKS

2  from v$sort_segment;

TABLESPACE_NAME     CURRENT_USERS TOTAL_BLOCKS USED_BLOCKS FREE_BLOCKS

------------------- ------------- ------------ ----------- -----------

TEMP                            0          120           0         120

You can see that this segment is split on 120 extents.  If you consider now the

storage clauses of the tablespace TEMP, you can change the storage parameters

to get a better allocation of sort segments using the ALTER TABLESPACE command.

SQL> select * from dba_tablespaces

2  where tablespace_name = 'TEMP';

TABLESPACE_NAME                INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS

------------------------------ -------------- ----------- -----------

MAX_EXTENTS PCT_INCREASE MIN_EXTLEN STATUS    CONTENTS  LOGGING   EXTENT_MAN

----------- ------------ ---------- --------- --------- --------- ----------

ALLOCATIO PLU

--------- ---

TEMP                                    65536       65536           1

0      65536 ONLINE    TEMPORARY LOGGING   DICTIONARY

USER      NO

These new storage clauses will be inherited only when recreating the sort

segment.  This can be done with the following sql command:

SQL> alter tablespace TEMP

2  default storage (pctincrease 0);

Please note, changing the default storage can only affect new objects, because of

which we need to create a new segment (to make the change effective). The old

segment (and its space) is released when it is no longer needed and since it

is cleaned up, the free space will be coalesced too.

This is the expected behaviour. If this is not desirable, then altering the tablespace

during normal operations should be avoided. Depending on the size of the original

segment, you could experience ORA-1562 errors.

If we query now the v$sort_segment:

SQL> select tablespace_name, current_users, total_blocks, used_blocks, free_blocks

2  from v$sort_segment;

no rows selected

In dba_segments, the same result is presented:

SQL> select owner, segment_name, segment_type from dba_segments

2  where tablespace_name = 'TEMP';

no rows selected

You can now affect new default storage clause associated with TEMP. On the

first next sort, the temporary sort segment will be recreated with the new

storage clauses.