Before You Back Up the Logical-Log Files

Home | Previous Page | Next Page The ontape Backup and Restore System (IDS) > Backing Up with ontape > Backing Up Logical-Log Files with ontape >

Before You Back Up the Logical-Log Files

Before you back up the logical-log files, you need to understand the following issues:

Whether you need to back up the logical-log files
When you need to back up the logical-log files
Whether you want to perform an automatic or continuous backup

For more information on these issues, see What Is a Logical-Log Backup?.

Using Blobspace TEXT and BYTE Data Types and Logical-Log Files

You must keep the following two points in mind when you use TEXT and BYTE data types in a database that uses transaction logging:

To ensure timely reuse of blobpages, back up logical-log files. When users delete TEXT or BYTE values in blobspaces, the blobpages do not become freed for reuse until you free the log file that contains the delete records. To free the log file, you must back it up.
When you must back up an unavailable blobspace, ontape skips it and makes it impossible to recover the TEXT or BYTE values when it becomes necessary. (However, blobpages from deleted TEXT or BYTE values do become free when the blobspace becomes available even though the TEXT or BYTE values were not backed up.)

In addition, regardless of whether the database uses transaction logging, when you create a blobspace or add a chunk to a blobspace, the blobspace or new chunk is not available for use until the logical-log file that records the event is not the current logical-log file. For information on switching logical-log files, see your IBM Informix: Administrator's Guide.

Using /dev/null When You Do Not Need to Recover

When you decide that you do not need to recover transactions or administrative database activities between backups, you can set the database server configuration parameter LTAPEDEV to /dev/null.

Warning:

When you set LTAPEDEV to /dev/null, it has the following implications:

You can only restore the data that your database server manages up to the point of your most recent backup and any previously backed-up logical-log files.
When you perform a recovery, you must always perform a full-system restore. (See A Full-System Restore.) You cannot perform partial restores or restore when the database server is online.

When you set LTAPEDEV to /dev/null, the database server marks a logical-log file as backed up (status B) as soon as it becomes full. The database server can then reuse that logical-log file without waiting for you to back it up. As a result, the database server does not preserve any logical-log records.

Fast recovery and rolling back transactions are not impaired when you use /dev/null as your log-file backup device. For a description of fast recovery, see your IBM Informix: Administrator's Guide. For information about rolling back transactions, see the ROLLBACK WORK statement in the IBM Informix: Guide to SQL Syntax.