gtpd1m0y | Database Reference |
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:
- The VFA buffer is being moved to the reserve chain because it failed the
buffer reuse threshold value test and the size of the reserve chain has fallen
below the specified percentage. This is known as force
filing.
- The TPF system is cycling from NORM state after entering the ZCYCL
command.
- The TPF system is cycling from NORM state after entering the ZRIPL
command.
- The TPF system is cycled to 1052 state after a ZRIPL command with the BP
parameter specified is entered or because of a catastrophic system error
resulting from a software IPL.
When a FILUC macro is processed, the delay filing attribute is handled in
one of the following ways:
- If the TPF system is running on a uniprocessor, delay filing is in
effect.
- If the TPF system is running in a loosely coupled environment and the
ZRTDM MODIFY command with the LOCKF parameter specified as DASD is entered,
then the delay filing attribute is ignored. The request is handled as
an immediate file.
- If the TPF system is running in a loosely coupled environment and the
ZRTDM MODIFY command with the LOCKF parameter specified as PROC is entered,
then delay filing is in effect and the updated copy remains in VFA on that
particular processor.
- 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.