What is undo tablespace in Oracle 11g?

What is undo tablespace in Oracle 11g?

Undo tablespace is a kind of permanent tablespace used by oracle database engine to manage undo data if you are running your database in automatic undo management mode. This undo data or undo records are generally used to: Roll back transactions when a ROLLBACK statement is issued. Recover the database.

How do I undo a Datafile in Oracle 11g?

How to Drop Undo Tablespace in Oracle Database

1. check whether the Undo tablespace to be dropped is the default Undo tablespace:
2. If the UNDO_TABLESPACE is set to the one to be dropped, create a new Undo tablespace and switch to the new one.
3. Check the status of the Undo segments in the Undo tablespace to be dropped.

How do I free up space on undo tablespace?

In order to remove datafiles added unnecessarily to UNDOTBS1 and reduce its size:

1. Create a new undo tablespace as : SQL> create undo tablespace UNDOTBS2 datafile.
2. Change parameter UNDO_TABLESPACE. SQL> alter system set UNDO_TABLESPACE=UNDOTBS2;
3. Drop UNDOTBS1.

Which undo tablespace is used?

From the above output, look for undo_tablespace. In this example, the current undo tablespace used by the oracle database is UNDOTBS.

How can I tell who is using undo tablespace?

Find session who generating lot of undo in Oracle

1. Find the session using more undo tablespace. select a.sid, a.serial#, a.username, b.used_urec used_undo_record, b.used_ublk used_undo_blocks.
2. Check the SQL TEXT using or generating undo segments.
3. Check the undo usage by session.

What is the purpose of undo tablespace in Oracle?

Oracle provides a fully automated mechanism, referred to as automatic undo management, for managing undo information and space. In this management mode, you create an undo tablespace, and the server automatically manages undo segments and space among the various active sessions.

What is Ora-01555 snapshot too old?

Error ORA-01555 contains the message, “snapshot too old.” This message appears as a result of an Oracle read consistency mechanism. If this occurs, you may encounter error ORA-01555 because the results outputted by Oracle must contain data as it appeared at 1:00PM before changes were made by the other user.

How do I change the undoRetention in Oracle 11g RAC?

Do one of the following:

1. Set UNDO_RETENTION in the initialization parameter file. UNDO_RETENTION = 1800.
2. Change UNDO_RETENTION at any time using the ALTER SYSTEM statement: ALTER SYSTEM SET UNDO_RETENTION = 2400;

What is unexpired undo in Oracle 11g?

12.2 RDBMS / GI and OL 7.4. Flashback enabled. UNDO_MANAGEMENT=AUTO, UNDO_RETENTION=900, MULTITENANT with local undo. I just wunder about many UNEXPIRED (20GB) UNDO extents. I know, that UNEXPIRED extents are reused if the UNDO Tablespace is out of space and the datafile isn’t extensible yet.

Do undo data survive the shutdown of a database?

It is persistent and can survive system crashes. That is, undo generated before an instance crash, is retained until its retention time has expired even across restarting the instance.

How do I monitor undo tablespace?

Check the Undo tablespace Usage in Oracle

1. Check the undo tablespace total, free and used space(Size in MB) in Oracle. SELECT a.tablespace_name,
2. Check the Active, expired and unexpired transaction space usage in Undo Tablespace.
3. Check undo usage by User or schema.