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How to Find Sessions Generating Lots of Redo

February 14, 2012 Leave a comment

When a transaction generates undo, it will automatically generate redo as well.

Methods to find sessions generating lots of redo:

1) Query V$SESS_IO.

This view contains the column BLOCK_CHANGES which indicates how much blocks have been changed by the session. High values indicate a session generating lots of redo.

SQL> SELECT s.sid, s.serial#, s.username, s.program,
 i.block_changes
 FROM v$session s, v$sess_io i
 WHERE s.sid = i.sid
 ORDER BY 5 desc, 1, 2, 3, 4;

Run the query multiple times and examine the delta between each occurrence of BLOCK_CHANGES. Large deltas indicate high redo generation by the session.

2) Query V$TRANSACTION.

These view contains information about the amount of undo blocks and undo records accessed by the transaction (as found in the USED_UBLK and USED_UREC columns).

SQL> SELECT s.sid, s.serial#, s.username, s.program,
 t.used_ublk, t.used_urec
 FROM v$session s, v$transaction t
 WHERE s.taddr = t.addr
 ORDER BY 5 desc, 6 desc, 1, 2, 3, 4;

Run the query multiple times and examine the delta between each occurrence of USED_UBLK and USED_UREC. Large deltas indicate high redo generation by the session.

You use the first query when you need to check for programs generating lots of redo when these programs activate more than one transaction. The latter query can be used to find out which particular transactions are generating redo.

Source: LOGGING OR NOLOGGING THAT IS THE QUESTION By Francisco Munoz Alvarez

How to check for LOGGING/NOLOGGING objects in the DB?

March 14, 2011 Leave a comment

Two example methods of querying the database for this information:

select owner , table_name, index_name
from dba_indexes
where logging='NO';

select tablespace_name, logging
from dba_tablespaces
/

Source: LOGGING OR NOLOGGING THAT IS THE QUESTION By Francisco Munoz Alvarez