Skip to Main Content
Oracle in a Nutshell
book

Oracle in a Nutshell

by Rick Greenwald, David C. Kreines
December 2002
Intermediate to advanced content levelIntermediate to advanced
928 pages
85h 29m
English
O'Reilly Media, Inc.
Content preview from Oracle in a Nutshell

Archived redo logs

While reading the previous explanation, you might have wondered how to avoid losing the critical information in the redo log when Oracle cycles over a previously used redo log.

There are actually two ways to address this issue. The first is quite simple: you don’t avoid losing the information, and you suffer the consequences in the event of a failure. You will lose the history stored in the redo file when it’s overwritten. If a failure occurs that damages the datafiles, you must restore the entire database to the point in time when the last backup occurred. No redo log history exists to reproduce the changes made since the time the last backup occurred, so you will be out of luck. Very few Oracle shops make this choice, because the inability to recover to the point of failure is unacceptable—it results in lost data.

The second and more practical way to address the issue caused by recycling redo logs is to archive the redo logs as they fill. To understand archiving redo logs, you must first understand that there are actually two types of redo logs for Oracle:

Online redo logs

The operating system files that Oracle cycles through to log the changes made to the database

Archived redo logs

Copies of the filled online redo logs made to avoid losing redo data as the online redo logs are overwritten

An Oracle database can run in one of two modes with respect to archiving redo logs:

NOARCHIVELOG

As the name implies, no redo logs are archived. As Oracle cycles around the logs, ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Oracle Internals

Oracle Internals

Donald K. Burleson
Oracle PL/SQL

Oracle PL/SQL

Lewis Cunningham
Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Rick Greenwald, Robert Stackowiak, Jonathan Stern

Publisher Resources

ISBN: 0596003366Errata Page