IDMS force buffer write

Products

• IDMS
• IDMS - Database

Issue/Introduction

An IDMS database area is shared between two CVs, i.e. the physical dataset of the area is shared between CV01 and CV02. The area in CV01 is always in update mode and the area in CV02 is always in retrieval mode . 

The problem is sometimes when the area is accessed in CV02, the old data is found, not the most recent updated data. How can this be avoided? 

Environment

Release: All supported releases.

Resolution

There are a couple of different features that can be used for sharing data across CV.

1. Shared Cache.
2. Data Sharing.
3. DCMT VARY AREA xxx PURGE, on which the remainder of this article will focus.
   The commands DCMT VARY AREA area-name PURGE or DCMT VARY SEGMENT segment-name PURGE will flush the buffers associated with the specified area or segment, forcing a new read on the next access of the record. The command(s) must be issued in the retrieval CV to update its buffers. Once the rununit on the update CV completes (issues a FINISH, COMMIT or ROLLBACK), the buffer pages associated with that rununit are all written to the database. When the purge is issued in the retrieval CV, it will only get updates for rununits that completed prior to the purge. It may be necessary to do the purge several times throughout the day, depending on the processing load. Shared cache is a better solution - the VARY PURGE can work, but would need to be coordinated with the update rununits.