Parameters Related to Performance

CLOSE_CHECK_INTV and DEFER_CLOSE_TIME

These parameters offer a trade-off between concurrency and PDSE processing performance. If typical usage on your system tends to reaccess the same or other members of a PDSE, these parameters can be specified as nonzero values to leave PDSEs open longer. Then, when PDSE members are reaccessed, the overhead of closing and reopening data sets is eliminated. The trade-off is that the data sets might be unavailable to other remote or local users longer than necessary.

MAX_AGENT_TSKS

This parameter can be used as a control on DFM resources. It determines the maximum number of concurrent remote user tasks that the target server will allow.

MAX_CONV_LOCK

This parameter establishes a limit on how many locks each agent can have. If you think of a lock as representing a system resource (in this case, a data set), then setting a maximum value for the number of locks that can be held establishes a limit on how much serially reusable resource a given agent can use at one time.

LOCK_RETRY and LOCK_WAIT_INTV

These parameters control how soon lock contentions are detected. In an interactive environment where you can choose how to handle “try again later” messages, you might want short wait intervals and few lock conflict retries. However, in a more batch-oriented environment, you might want the opposite to avoid terminating batch jobs just because a lock is temporarily unavailable.

SEND_BUFFER_THRESHOLD

For this parameter, the maximum number of buffers between APPC SEND verb completions should be fairly large to avoid irregularities in system response and to maximize concurrency. Specifying too large a value, however, could result in excess paging.

In some cases, this parameter can increase the overall auxiliary storage requirements of the system. As a general rule, you can determine the auxiliary storage increase by adding up the estimates for the following:

The total size of the stream-oriented files that are likely to be accessed concurrently by a typical address space
The space required for input buffers (up to the combined file size)
The storage required for output buffers (SEND_BUFFER_THRESHOLD times 32k)

Take the resulting sum and multiply it by the number of concurrently running address spaces, then add 25% to allow for control block overhead and unused space at the end of some of the buffers.

LOGICAL_CACHE

This parameter allows you to limit the amount of virtual storage a DFM conversation can use for caching stream files. When the limit is reached, the current stream request is terminated. You can use this parameter to minimize the potential impact of DFM for z/OS® on z/OS system performance.