海洋之神BB电子

書名： Oracle Database 12c Backup and Recovery Survival Guide
作者名： Francisco Munoz Alvarez Aman Sharma
本章字數： 253字
更新時間： 2021-04-02 10:19:59

Finding sessions that generate 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.

Query v$sess_io: This view contains the column block_changes, which indicates how many 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,
i.block_changes
 2 FROM v$session s, v$sess_io i
 3 WHERE s.sid = i.sid
 4 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.
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, 
t.used_ublk, t.used_urec
 2 FROM v$session s, v$transaction t
 3 WHERE s.taddr = t.addr
 4 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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Oracle Database 12c Backup and Recovery Survival Guide

Finding sessions that generate lots of redo