RRS Help

RRS uses 6 log streams, one for each of its 6 logs. Only 4 are required. The archive and metadata logs are optional, although the archive log is recommended.

Each non-DASD-only log stream must be mapped to a coupling facility structure in the LOGR policy. A basic structure mapping would assign each of the RRS log streams to a separate structure. You can map multiple log streams to a single structure, but log streams sharing a structure should have similar write rates to ensure that structure resources are shared equitably between the streams. IBM recommends that each RRS log stream reside in its own coupling facility structure. This recommendation is particularly important for the archive log. Allowing the RRS archive log stream to share its coupling facility structure with another log stream is likely to result in suboptimal use of the storage in the coupling facility structure, which could affect system performance.

To calculate the size of an RRS log structure, provide the following input data:

Log stream

Select the log streams that you want to assign to a single log structure. For example, clicking MAIN.UR and RM.DATA sizes a single log structure large enough to contain these two log streams. Submit a separate sizing request for each log structure.

MAIN.UR

The UR is logged multiple times during its processing. Use SMF type 88 records to estimate writes per second at peak transaction rates, and add some room for growth.

DELAYED.UR

The UR is logged multiple times during its processing. Use SMF type 88 records to estimate writes per second at peak transaction rates, and add some room for growth.

ARCHIVE

Use monitor reports or SMF records that indicate the number of writes per second for all resource managers that use RRS. Set Writes Per Second for the ARCHIVE log equal to the sum plus some room for growth. In general, we recommend that you use data from monitor reports from an interval with high logging activity to accommodate spikes in the workload. For example, suppose that SMF type 88 records (SMF88LWI) show that 5000 IXGWRITEs were issued during the busiest expiring SMF interval for this log stream. If the expiring SMF interval is 30 minutes, then the following calculation yields the value for writes per second:

(5000 writes/ 30 minutes) x (1 minute / 60 seconds) = 2.78 writes / second

Leaving some room for growth, the Writes Per Second could be set to 5. For additional information on reviewing SMF type 88 records, review the z/OS MVS System Management Facilities (SMF) manual under topic Record Type 88 (58) - System Logger Data.

RM.DATA

Because this log is infrequently updated, use 10.

RESTART

This log contains only the information about a UR that a resource manager would need at restart. Set Writes Per Second to the same value you set for ARCHIVE.

RM.METADATA

Because this log is infrequently updated, use 10.

Writes per second

Enter your estimate of the number of times that RRS writes to the log stream each second. All the systems in the sysplex can share the RRS log streams, so you must take all the systems into account. Also, RRS writes to each log stream at different rates, so you will probably have different estimates for different log streams.