Main storage (memory) and save-while active

 

How a save-while-active operation affects main storage depends on three items,

 

Parent topic:

Performance considerations for save-while-active

 

Pageable size of the machine pool

Additional pages are required in the machine pool for the system to use during the save-while-active operation. Additionally, saving many small objects or file members places additional requirements on the pageable portion of the machine pool. You should consider the addition of 1200KB to the machine pool a minimum. Additional memory may improve the response time and the save-time.

Additional megabytes of storage for the machine pool may help performance if saving thousands of small objects or file members (less than 50KB object sizes). You should monitor the machine pool for paging activity.

 

Job priority and pool usage

You must decide which jobs have priority: the save operation or the other activity on the system. You should give the save operation a lower priority than the interactive jobs, but a higher priority than other batch jobs. This priority will maintain the best response time for interactive jobs, but still allow the save to complete as quickly as possible. In addition, separate the save operation from other work on your system by using a separate memory pool. The size of this separate pool should be a minimum of 10MB (16MB if you are using a high speed tape device). The full synchronization and library synchronization options generally require a few additional megabytes of memory. If there are thousands of objects or file members in the save-while-active operation, you should add more memory to the memory pool. This is especially true if the objects are small. To determine the correct pool size for your system, monitor the paging activity in the pool during a save and adjust the memory as necessary. However, if the pool is a shared memory pool, then the settings in the system value, QPFRADJ, will adjust its performance.

 

Number and size of objects

If you are saving many small objects or file members, the paging in the machine pool may increase. You should monitor paging in the machine pool. You should take steps to minimize paging to maintain better overall system performance. These recommendations are also apply for normal save and restore operations.