Informix Guide to SQL: Tutorial

Informix Guide to SQL: Tutorial
Chapter 4: Modifying Data

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Backups and Logs

By using transactions, you can ensure that the database is always in a consistent state and that your modifications are properly recorded on disk. But the disk itself is not perfectly safe. It is vulnerable to mechanical failures and to flood, fire, and earthquake. The only safeguard is to keep multiple copies of the data. These redundant copies are called backup copies.

The transaction log (also called the logical log) complements the backup copy of a database. Its contents are a history of all modifications that occurred since the last time the database was backed up. If you ever need to restore the database from the backup copy, you can use the transaction log to roll the database forward to its most recent state.

Backing Up with INFORMIX-Universal Server

Universal Server contains elaborate features to support backups and logging. They are described in the INFORMIX-Universal Server Archive and Backup Guide.

If you want to make a personal backup copy of a single database or table that is held by Universal Server, you can do it with the onunload utility. This program copies a table or a database to tape. Its output consists of binary images of the disk pages as they were stored in Universal Server. As a result, the copy can be made very quickly, and the corresponding onload program can restore the file very quickly. However, the data format is not meaningful to any other programs.

If your Universal Server administrator is using ON-Archive to create backups and back up logical logs, you might also be able to create your own backup copies using ON-Archive. For more information, see your INFORMIX-Universal Server Archive and Backup Guide.

Informix Guide to SQL: Tutorial, version 9.1
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