Backups and logs with HCL OneDB database servers

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.

The database server contains elaborate features to support backups and logging. Your database server archive and backup guide describes these features.

The database server has stringent requirements for performance and reliability (for example, it supports making backup copies while databases are in use).

The database server manages its own disk space, which is devoted to logging.

The database server performs logging concurrently for all databases using a limited set of log files. The log files can be copied to another medium (backed up) while transactions are active.

Database users never have to be concerned with these facilities because the DBA usually manages them from a central location.

HCL OneDB™ supports the onload and onunload utilities. Use the onunload utility to make a personal backup copy of a single database or table. 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 the database server. As a result, the copy can be made quickly, and the corresponding onload program can restore the file quickly. However, the data format is not meaningful to any other programs. For information about how to use the onload and onunload utilities, see the HCL OneDB Migration Guide.

If your DBA uses ON-Bar to create backups and back up logical logs, you might also be able to create your own backup copies using ON-Bar. For more information, see your HCL OneDB Backup and Restore Guide.