gtpd1m0yDatabase Reference

VFA Record Selection

Use the ZRTDM MODIFY command to define fixed file records or pool records as VFA candidates. See TPF Operations for more information about the ZRTDM MODIFY command.

You can define each record group with the following attributes:

Delay Filing
When an application program issues a FILEC or FILNC macro for a delay filing candidate, the update is noted in the VFA buffer but the updated record is not physically filed to DASD. This reduces the amount of physical I/O activity when VFA candidate records are repeatedly filed.

The record is physically filed to DASD during the following conditions:

When a FILUC macro is processed, the delay filing attribute is handled in one of the following ways:

Synchronized Delay Filing
Records are handled the same way as normal delay filing records described previously with the addition that a synchronized delay file candidate is filed when another processor requests the record and database consistency can be maintained if multiple processors update the record.

Immediate Filing
FILEC, FILNC, and FILUC macros are processed in the conventional way; the record is physically filed to DASD. Immediate filing occurs for delayed file records when the TPF system is not in NORM state.

Synchronized Immediate Filing
Records are handled the same way as normal immediate filing records described previously with the addition that database consistency is maintained if multiple processors update the record.

DASD Locking
Records that are to be held for exclusive use are fetched from DASD so that the external lock facility (XLF) can grant exclusive use to one processor. This is the default setting. Any record that will be altered should have this attribute.

Processor Locking
A record that is used in a read only capacity or is processor unique bypasses the XLF when the record is located in VFA. The VFA copy is fetched and no DASD I/O is performed.

Attention: Do not consider this option unless extremely high performance is warranted. Because the external lock facility is bypassed, the data integrity of the record may be compromised.

General Data Set Record
A special VFA candidacy condition exists for certain general data set (GDS) records. Index records that are associated with virtual storage access method (VSAM) data sets mounted to the TPF system are cached in VFA for performance reasons. VSAM record access requires an associated key lookup using an index data set; caching these index records eliminates the need for repeated accesses to DASD. The TPF system selects GDS record candidates internally; that is, the ZRTDM command cannot be used to select GDS record candidacy.