User PFA caching

Please note the user PFA are supported for the last time in OSD/BC V11.0!

In user PFA caching (PFA: Performant File Access), systems support decide which pubsets are assigned a cache area, which properties this cache area is to have and which users are to benefit from the caching of these pubsets.
You will find a detailed description of this in the “Introduction to System Administration” [10 (Related publications)].

PFA from the user's perspective

Depending on the definition of the cache area, the use of a PFA cache for a pubset can be either global for all files or selective for specific files:

• If the cache area is defined with the attribute CACHED-FILES=*BY-SYSTEM (i.e. AutoDAB is in use) or CACHED-FILES=*ALL (all user files of the pubset are subject to the caching), the user does not need to perform any further actions in order to benefit from caching on this pubset.

• If the cache area is defined with CACHED-FILES=*BY-USER-SELECTED, the caching as described below only affects files with the corresponding attribute.

The commands /CREATE-FILE, /MODIFY-FILE-ATTRIBUTES and /ADD-FILE-LINK and the macros FILE and CATAL can be used to assign the following file attributes:

Operand	Meaning
PERFORMANCE	Specifies caching behavior (main memory):
= *STD	no caching
= *HIGH	caching with preemption on the basis of LRU
= *VERY-HIGH	caching without preemption
= *USER-MAX	highest performance attribute for which the user has authorization
USAGE	Improved performance requirements apply:
= *READ-WRITE	to read and write operations
= *READ	to read operations onl
= *WRITE	to write operations only
DISK-WRITE	Data consistency is restored:
= *IMMEDIATE	after every write operation (prerequisite: non-volatile cache medium)
= *BY-CLOSE	not until after CLOSE processing
= *STD	*IMMEDIATE applies for permanent files, *BY-CLOSE applies for temporary files

If the same files are opened and closed several times during continuation processing (generally in batch mode), the user can further improve throughput by doing the following when closing the file:

• preventing the invalidation of the read data in the cache

• suppressing the saving of the write data in the cache (only recommended for temporary files in the case of a volatile storage medium).

Another advantage is that reopened files do not have to be stored in the cache again. This type of PFA caching (HIPERBATCH = high-performance batch processing) is made possible by the operand CLOSE-MODE= *KEEP-DATA-IN-CACHE of /ADD-FILE-LINK and the KEEP-DATA-IN-CACHE operand of the CLOSE macro.

PFA from the point of view of systems support

In order for the user's performance requirements to become effective, corresponding authorizations must be entered in the user catalog (/ADD-USER, /MODIFY-USER-ATTRIBUTES or /MODIFY-USER-PUBSET-ATTRIBUTES):

Operand	Meaning
DMS-TUNING-RESOURCES	Defines performance measures
= *NONE	caching not permitted
= *CONCURRENT-USE	for request PERFORMANCE=*HIGH
= *EXCLUSIVE-USE	for request PERFORMANCE=*VERY-HIGH
PERM-/TEMP-/WORK-SPACE-LIMIT    = *PARAMETERS(...)	Defining the users' storage space quotas (in each case for permanent, temporary, and work files):
HIGH-PERF-SPACE= ...	for high-performance storage space
VERY-HIGH-PERF-SPACE= ...	for very high-performance storage space

You must ensure that the authorization and storage space quotas are entered in the user catalog of the pubset on which the file is located.

Systems support uses the following commands to control the use of PFA caching:

Command	Function
MODIFY-PUBSET-CACHE- ATTRIBUTES	Specifies the cache area attributes in the MRSCAT of a pubset/volume set
IMPORT-/EXPORT-PUBSET	Implicitly creates or deletes a cache area described in the MRSCAT
START-/STOP-PUBSET-CACHING	Dynamically creates or deletes a cache area described in the MRSCAT during a pubset session
SHOW-CACHE-CONFIGURATION	Outputs PFA cache area configuration
SHOW-PUBSET-CACHE-ATTRIBUTES	Outputs a cache area description in the static and dynamic MRSCAT
FORCE-DESTROY-CACHE	Forces the deletion of a PFA cache area
MODIFY-PUBSET-DEFINITION- FILE	Defines (logical) performance characteristics of a volume set of an SM pubset
MODIFY-PUBSET-PROCESSING	Implicitly creates or deletes cache areas when actively adding or removing volume sets to or from an SM pubset

The cache medium for the corresponding pubset is defined by means of the operands of /MODIFY-PUBSET-CACHE-ATTRIBUTES:

Operand	Meaning
CACHE-MEDIUM	Specifies the cache medium:
=*MAIN-MEMORY	Main memory
CACHE-SIZE=n	Size of the cache area
FORCE-OUT	Specifies how full the cache has to be before the contents are saved on disk:
=*AT-HIGH-FILLING	75%
=*AT-LOW-FILLING	25%
=*NO	No saving at intervals

In addition, the following information is important for the CACHE-MEDIUM operand:

Operand	Meaning
CACHE-SEGMENT-SIZE	Size of a cache segment (i.e. the minimum size of the data area stored if there is a read miss):
=*4KB/*8KB/*16KB/*32KB	4, 8, 16 or 32 KB (only relevant for non-automatic cache areas)
CACHED-FILES	Specifies which files should use the cache.
=*BY-USER-SELECTED	The user uses performance attributes to specify which of his/her files should use the cache.
=*ALL	All user files use the cache.
=*BY-SYSTEM	Automatic cache area: the automatic, intelligent caching of the AutoDAB means that the files relevant to performance are determined automatically; the prefetch factor matching the access profile of the selected files is set, and the files are monitored cyclically to guarantee optimum cache performance.

User PFA caching is required for a shared pubset when local write caching is to be supported for each server (with ADM-PFA caching, only read caching is possible).