IDMS Unload/Reload DIRECT records placement

Products

• IDMS
• IDMS - Database

Issue/Introduction

An IDMS database area may contain records that are defined LOCATION MODE DIRECT. The programs that STORE these records move -1 to DIRECT-DBKEY prior to the STORE so the records are stored in a physical sequential order in the area.

When an Unload/Reload of the area is done to increase the page size, it was expected that the reload utility would completely fill the new larger pages with these records, in the same order as they were in the existing area. However it appears that each record was stored on the same page on which it existed in the existing area so the new additional space on each page was not used during reload.

Why did the reload not fill the new larger pages?

Environment

Release: All supported releases.

Resolution

The UNLOAD utility uses the new DMCL to determine target pages in the new area for each record unloaded. For DIRECT records, if the existing page on which they are stored exists in the new area definition in the new DMCL, then the target page in the new area is the same page number.

The unloaded record's page is extracted from the dbkey and compared against the new area's page range. If the current page number is within the new page range, that page becomes the target page within the new database. If the current page number is higher than or lower than the new page range the low page of the new area is selected as the target page. 

For those pages that exist in both the old and new page range, if the new pages are larger they should expect to see space remaining on those pages because only the number of records that targeted to the old page would be targeted to the new page.

To get the Unload/Reload to fill up the new larger pages with these DIRECT records in the same order, the easiest way to accomplish this is to assign the area a completely different page range in the new DMCL, which would cause the target page to be the area low page for each record.

User written unload and reload programs could be another method but could be a complex process if the records also participate in sets.