Question

Can any body give me an idea about Redo logs? An example would be most appreciated.

Answer 1

As Oracle changes data in a datafile, it writes out information to the redo log. In the event of a database failure, you can use this information to get the database back to the point it was before the database failure.

In a disaster recovery scenario, you could restore your last full database backup, and then apply the redo logs taken since that last backup to get the database recovered. Without those redo logs, you could only recover to the last full backup, and changes made since then would be lost.

In Oracle, you can also run in “no archive log mode”, which basically means, “redo logs can be overwritten without being saved”. This is generally only acceptable for a development database where you don’t care about losing data since the last backup. You wouldn’t typically run in this mode in a production environment, as it could be disastrous.

Here’s a reference link with more info, and also an example of how you can find out the amount of generated redo.

http://www.adp-gmbh.ch/ora/concepts/redo_log.html