How to clean undotablespace

Question

how to clean undotablespace its using 10 GB space in my HDD

Answer 1

Salman Qureshi wrote:
What is the reason to clean it? Apparently he's running with "an HDD" - so perhaps he's short of space and a runaway process has made the undo tablespace grow much larger than normal. Creating a new one and switching into it might be his best strategy - although he might like to consider ways to stop the accident happening again (e.g. setting a very small undo_retention_time, or not allowing the file to grow automatically - if he can live with processes terminating with "out of space" conditions.)
>
Another way is to cleanly shutdown and then start your database (if not production and downtime is acceptable). When DB is started, you will see tablespace empty and now you can shrink file or even try dropping a data file.
That's the second time in a week that I've heard the story that a database shutdown will empty the undo tablespace. It's not true.
Depending on version you may find a much smaller number of undo segments are brought online when you restart the database and smon does, from time to time, drop undo segments, but (a) Oracle generally avoids doing work that isn't necessary, and (b) Oracle generally avoids destroying information that might be useful, so it's very slow to drop undo segments.
Quick check on a toy database:
SQL> select tablespace_name , contents  from dba_tablespaces;
TABLESPACE_NAME                CONTENTS
SYSTEM                         PERMANENT
UNDOTBS1                       UNDO
SYSAUX                         PERMANENT
TEMP                           TEMPORARY
USERS                          PERMANENT
TEST_8K                        PERMANENT
6 rows selected.
SQL> select count(*) from dba_segments where tablespace_name = 'UNDOTBS1';
  COUNT(*)
        33
1 row selected.
SQL> startup force
ORACLE instance started.
Total System Global Area  297795584 bytes
Fixed Size                  1290232 bytes
Variable Size             159383560 bytes
Database Buffers          130023424 bytes
Redo Buffers                7098368 bytes
Database mounted.
Database opened.
SQL> select count(*) from dba_segments where tablespace_name = 'UNDOTBS1';
  COUNT(*)
        33
1 row selected.Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
A general reminder about "Forum Etiquette / Reward Points": http://forums.oracle.com/forums/ann.jspa?annID=718
If you never mark your questions as answered people will eventually decide that it's not worth trying to answer you because they will never know whether or not their answer has been of any use, or whether you even bothered to read it.
It is also important to mark answers that you thought helpful - again it lets other people know that you appreciate their help, but it also acts as a pointer for other people when they are researching the same question, moreover it means that when you mark a bad or wrong answer as helpful someone may be prompted to tell you (and the rest of the forum) what's so bad or wrong about the answer you found helpful.