Diagnosing Excessive Redo Generation - Limit with Nologging (Doc ID 199298.1)

Last updated on SEPTEMBER 20, 2023

Applies to:

Purpose

To help with diagnosing excessive redo generation.

First, some background on redo generation:

What is the Online Redo Log?
The most crucial structure for recovery operations is the online redo log,
which consists of two or more pre-allocated files that store all changes made
to the database as they occur. Every instance of an Oracle database has an
associated online redo log to protect the database in case of an instance
failure.

What are the contents of the Online Redo Log?
Online redo log files are filled with redo records. A redo record, also called
a redo entry, is made up of a group of change vectors, each of which is a
description of a change made to a single block in the database. For example,
if you change a salary value in an employee table, you generate a redo record
containing change vectors that describe changes to the data segment block for
the table, the rollback segment data block, and the transaction table of the
rollback segments.

Redo entries record data that you can use to reconstruct all changes made to
the database, including the rollback segments. Therefore, the online redo log
also protects rollback data. When you recover the database using redo data,
Oracle reads the change vectors in the redo records and applies the changes
to the relevant blocks.

Troubleshooting Steps