Find Session Generating a lot of REDO in Oracle

Archive logs [ID 167492.1]


To find sessions generating lots of redo, you can use either of the following

methods. Both methods examine the amount of undo generated. When a transaction

generates undo, it will automatically generate redo as well.



The methods are:

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.



The query you can use is:

SQL> SELECT s.sid, s.serial#, s.username, s.program,

2 i.block_changes

3 FROM v$session s, v$sess_io i

4 WHERE s.sid = i.sid

5 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. This 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).



The query you can use is:

SQL> SELECT s.sid, s.serial#, s.username, s.program,

2 t.used_ublk, t.used_urec

3 FROM v$session s, v$transaction t

4 WHERE s.taddr = t.addr

5 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.