What are the pros/cons for a site in using the Sysplex Coupling Facility for the ACF2 databases versus the ACF2 Cache Facility?
Article ID: 35453
Updated On:
Products
Issue/Introduction
What are the pros/cons for a site in using the Sysplex Coupling Facility for the ACF2 databases versus the ACF2 Cache Facility?
Environment
Component: ACF2MS
Resolution
Key points regarding the ACF2 Cache Facility versus the Sysplex Coupling facility.
The XES data sharing feature lets the customer define structures in the SYSPLEX that multiple systems can use. These structures contain data to be shared between these systems. Once the data has been placed in the structure it is valid to be read, updated, or deleted by any system connected to that structure.
The purpose of putting ACF2 records in the sysplex coupling facility is to minimize I/O. I/O to the RULES and INFOSTG databases can be minimized by making commonly used rules and profiles resident in storage via the INFODIR record. That leaves only the logonid records from the LID database as being a source for significant I/O. Generally, since there is more READ I/O than WRITE I/O, and since RESERVEs are only issued for WRITES, if you put the lid records in the SYSPLEX coupling facility where they are available for READs, there would only be I/O to the database when they are updated.
Most clients only specify lids in the coupling facility since they make commonly used rules and profiles resident in storage via the GSO INFODIR as RESRULE records.
Performance would have to be measured by one of the generally available monitors, such as MAINVIEW and OMEGAMON. CA does not provide a performance measurement tool applicable to SYSPLEX coupling.
XES Coupling Facility Advantages:
- Records are kept in a Coupling Facility structure
- No database ENQ by requestor
- I/O is processed concurrently
Considerations:
- Its only used for individual read requests
- Read for update and sequential processing is ignored **
- Requires use of the Coupling Facility
- Limited to the speed of the Coupling Facility device
** Any read for updates to a logonid record are done to the database before the update occurs in the Coupling Facility. A sequential read such as a TSO, ACF, LIST like(mask) would be done to the database rather than to the Coupling Facility.
ACF2 Cache advantages:
- No need for special hardware or software
- I/O processed concurrently
- No waiting on write requests
- Records kept in the ACF2 address space
- No database ENQ by requestor
Considerations:
- Sequential processing
- Requires GSO SYNCOPTS when sharing the database At this point it is difficult to say one is better than the other. Every site's environment is different, we recommend that a site evaluates their configuration and system performance to determine which tool will best suit their needs.
Additional Information
Details on the ACF2 Cache Facility and the SYSPLEX Coupling Facility can be found in the CA ACF2 for z/OS Administration Guide section: 'Cache Records' and 'SYSPLEX Coupling Facility'.
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