How to Find Sessions Generating Lots of Redo

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.

.

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Sobre Alexandre Pires

ORACLE OCS Goldengate Specialist, OCE RAC 10g R2, OCP 12C, 11g, 10g , 9i e 8i - Mais de 25 anos de experiência na área de TI. Participei de projetos na G&P alocado na TOK STOK, EDINFOR alocado na TV CIDADE "NET", 3CON Alocado no PÃO DE AÇUCAR, DISCOVER alocado na VIVO, BANCO IBI e TIVIT, SPC BRASIL, UOLDIVEO alocado no CARREFOUR e atualmente na ORACLE ACS atendendo os seguintes projetos: VIVO, CLARO, TIM, CIELO, CAIXA SEGUROS, MAPFRE, PORTO SEGURO, SULAMERICA, BRADESCO SEGUROS, BANCO BRADESCO, BASA, SANTANDER, CNJ, TSE, ELETROPAULO, EDP, SKY, NATURA, ODEBRESHT, NISSEI, SICREDI, CELEPAR, TAM, TIVIT, IBM, SMILES, CELEPAR, SERPRO,OKI,BANCO PAN, etc
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