For a coupling facility log stream, applications can influence the frequency of off-loads and the processing overhead offloading entails by sizing their coupling facility structure carefully. The larger the coupling facility structure, the less often offloading processing will occur and the larger the chunk of data that will be off-loaded. This minimizes offloading overhead and keeps more log data available on the coupling facility structure for high performance reads of log data.

For example, if you have a log stream with a high volume of data being written to it, and you have allocated a small coupling facility structure for this log stream, the coupling facility structure will fill quickly and meet its high threshold, initiating frequent offloading of log data to DASD. This increases system usage, but does not interfere with processing of write requests to the log stream, because write requests can run at the same time as offload processing.

However, the coupling facility structure for a log stream should not be larger than the application really requires and should reflect the needs of the rest of the installation for coupling facility space. See Determine the size of each coupling facility structure for information about optimal sizing of coupling facility structures for response, throughput, and availability.

If the coupling facility space allocated for a log stream reaches 100% utilization, all write requests against that log stream are rejected until offloading can complete.