Absolute File Integrity

How to:

FOCUS can perform shadow paging to guarantee the integrity of any FOCUS data source created. This option does require extra disk space, so it is up to the Database Administrator to decide whether Absolute File Integrity is necessary for the data source.

FOCUS shadow paging is accomplished by checkpoints and directory pages, which, in one stroke, changes the shadow pages into current database pages. Basically, FOCUS creates a shadow image of a FOCUS data source, with each FOCUS page having a corresponding shadow page. At any point, one of the data source images has complete data integrity, regardless of what happens to the other. Therefore, the data integrity of a FOCUS data source will never be compromised by a system crash or other circumstances.

Absolute File Integrity is available for FOCUS data sources in all operating system environments.

Note: Absolute file integrity is not supported for XFOCUS data sources.
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Syntax: How to Invoke Absolute File Integrity

To invoke Absolute File Integrity in FOCUS before creating the data source with the CREATE FILE command, issue the following 

SET SHADOW = value

where:

value

Can be one of the following:

OFF does not invoke Absolute File Integrity. OFF is the default value.

ON invokes Absolute File Integrity.

OLD invokes the use of the shadow technology available in FOCUS releases prior to 7.0 (before the size limit for FOCUS data sources was increased), meaning fewer pages are shadowed. If your FOCUS data source was created with this option, the maximum number of pages is 63,551. If this limit is exceeded, FOCUS displays the (FOC198) error message.
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Procedure: How to Invoke Absolute File Integrity for an Existing Data Source

If the data source has already been created, take the following steps to invoke Absolute File Integrity:

  1. Specify the REBUILD, REORG, and DUMP options with the REBUILD command.
  2. Invoke the Absolute File Integrity facility with the SET SHADOW=ON command.
  3. Create the FOCUS data source with the CREATE FILE command.
  4. Specify the REBUILD, REORG, and LOAD options with the REBUILD command.

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