What are the journals used for?

Products

• Dispatch Output Mgmt

Issue/Introduction

Describe how Dispatch uses the four journals.

Resolution

Dispatch utilizes 4 journals. These are periodically dumped by Dispatch when they become full.

Dispatch uses an IDMS database. All updates and modifications to the database are logged in the journals. A ?Before? and ?After? image is written to the journals during each update. These Before/After images are used by IDMS to protect the database from broken chains.

As an example, when adding a new recipient to a report definition, from the Report Base Definition Screen, you enter an X5 to add a new recipient. When doing this, you are actually opening a report-base record in update mode. A Before-image will be written to the journals. If, while the new recipient is being added, there is an interruption and Dispatch is cancelled, the IDMS CV (Central Version) will use the Before-image to make the database look as it did before the attempted change. In the example given, when Dispatch is brought back up, you would see a message indicating that 'Run-unit id xxxx is being rolled back' (Any database activity in IDMS is called a run-unit).
If no interrupt occurs and the addition of the new recipient is completed, then an After-image will be recorded.
When a journal is dumped, Before-images are matched with After-images and if there is a match, the images are dumped to the offload media. Any Before-images without a corresponding After-image will be condensed and moved to the beginning of the journal dataset so that they would be available if a run-unit had to be rolled out. This is why the journals rarely show as completely empty.