OS/390 Parallel Sysplex Configuration, Volume 2: Cookbook

2.1 CF Structures Overview

Within the CF, storage is dynamically partitioned into structures. OS/390 (XES)

services can then manipulate data within the structures. Each of the following

structure types has unique functions:

Cache structures

Sharing CPCs can use the CF to cache shared data. Three types of caching

are done: cache

directory-only

, cache

store-through

, and cache

store-in

. All

cache structures have directory entries. The store-through and store-in

structures also have data entries.

Directory-only caching consists of a directory element that records which

users have an interest in a particular shared piece of data. The actual

shared data does not exist in the CF structure.

For cache store-through, the data is written to the CF structure and also to

DASD immediately.

For cache store-in, DASD is written to the CF structure, and to DASD at some

later time.

For shared data caches using the CF, cross-invalidation of local buffers is

done automatically. Examples of the use of caching are:

−

For members in the data sharing group, IMS/ESA V5 uses cache

structures for OSAM and VSAM buffers. Here, the cache structures are

used to manage the

integrity

of data in the local buffer pools. This is an

example of directory-only usage of the cache.

−

CICS/VSAM RLS uses cache structures to maintain buffer and data

consistency at the control interval (CI) level of all systems in a Parallel

Sysplex. CICS/VSAM RLS uses the cache structure for store-through

caching; that is, data is written to DASD as well as to the cache

structure. Status is returned to the subsystem when both the CF write

and DASD write have completed.

IMS/ESA V6 has an option to use a store-through cache for OSAM data

sharing in a similar fashion.

RACF or OS/390 Security Server uses a cache structure to quickly access

frequently used information located in the database. Store-through

caches are used for the RACF primary and backup databases.

−

DB2 uses a cache structure to store buffer pool data, which is later read

back to DB2 to be written to DASD. This is an example of cache store-in.

−

DFSMS/MVS V1.5 Enhanced Catalog Sharing (ECS) uses a cache

structure to store catalog sharing information that was previously kept in

the VVDS.

The ECS use of the cache structure is a unique implementation in that

information that is written to the cache structure is never written to

DASD. The cross-invalidation feature of cache structures is used to

inform the Catalog Address Spaces if another system updates a catalog

record that they have an in-storage copy of. If the cache structure

becomes unavailable, all in-storage catalog records are marked as being

invalid, and the Catalog Address Space reverts to using the VVDS to

store catalog integrity information.

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Parallel Sysplex Configuration, Volume 2: Cookbook

Lock structures

Centralized lock tables are used in the CF to provide synchronous

serialization and contention detection. Following are examples of the use of

locking:

−

The CF is used as a high-speed locking facility by the Integrated

Resource Lock Manager (IRLM), which in turn supports IMS DB and DB2

data sharing.

−

CICS/VSAM RLS uses the locking function of the CF to provide

record-level locking.

−

GRS star support uses the contention detection and management

capability of the lock structure to determine and assign ownership of a

particular global resource.

List Structures

List structures provide shared queues and shared status information.

Messages can be exchanged using CF list structures to implement

high-performance data sharing. The following are examples of list structure

usage:

−

JES2 uses the list structure for shared work queues. JES2 can place the

checkpoint data set in the CF to exchange job information between

systems. When a system accesses the checkpoint, it can review all

changes from other systems and add its own updates, without having to

serialize on a DASD volume.

−

OS/390 Communications Server and VTAM use a list structure for shared

status generic resource information.

−

DB2 uses a list structure for the Shared Communication Area. This is

used for inter-DB2 communication and also to record status information

about shared databases.

−

The system logger component of OS/390 may be used by, for example,

OPERLOG to create a single logstream in a list structure.

−

XCF may use the list structure for message passing. Prior to the CF,

channel-to-channel (CTC) links were required between each

communicating processing unit.

XCF message passing exploitation includes:

- GRS ring processing (not applicable to GRS star configurations)

- Workload Manager (WLM), to pass performance management data

among systems in the sysplex

- IRLM uses XCF to exchange lock information between IRLM

instances on multiple systems

- CICS, for MRO requests between images

- JESXCF, which in turn may be used by

JES2, to send messages for checkpoint error or reconfiguration

JES3, to do cross-system communication

TCAS, invokes JESXCF as part of the generic logon processing

- Console, for multisystem message passing

- VLF, to send messages

Chapter 2. A Structured View of CF Structures

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