Functions that increase the journal receiver size
Some optional functions available with journal management can significantly increase auxiliary storage requirements.
You can select to journal both before-images and after-images. The system uses more storage if you select both before-images and after-images, although storage use is not necessarily doubled. If you journal access paths, the before-images and after-images are written to the journal receiver when a database file is updated. Only after-images are written when a database file is added (write operation) or deleted. Neither the before-image nor after-image is deposited into the journal if the after-image is exactly the same as the before-image.
Using Fixed-length options for journal entries can also increase auxiliary storage requirements. The additional storage that fixed-length options use is similar to the extra space that is used by journaling both before-images after-images.
The system requires additional space to journal access paths. The space required depends on the following items:
- How many access paths are journaled.
- How often you change the access paths. When you update a record in a database file, you cause an access path journal entry only if you update a field included in the access path.
- The method used to update access paths. More journal entries are written if you update access paths randomly than if you update them in ascending or descending sequence. Doing a mass change to an access path field, such as a date change, causes the fewest journal entries.
If you are using system-managed access-path protection and you journal database files, the system uses the same journal receiver to protect access paths for that file. This also increases the size of your journal receivers.
The information in Methods to estimate a journal receiver will help you predict your requirements for auxiliary storage.
Parent topic:
Planning for journal use of auxiliary storageRelated concepts
Fixed-length options for journal entries System-managed access-path protectionRelated tasks
Methods to estimate the size of a journal receiver