DB2 Server for VSE & VM: Performance Tuning Handbook

VSE Specifics

Dispatching Priority

The database partition should be configured according to the following guidelines:

• Set its priority lower than any CICS partitions that are accessing it.
• Set its priority immediately below the CICS partition with the lowest priority that is accessing it.
• Set its priority higher than any batch partitions accessing it.
• Do not include it in a partition balancing pool.

Fast CCW Translation

Do not use fast CCW translation (FASTTR job control option) in the database or CICS partitions. Include the following option card in the application server start up job:

   // OPTION NOFASTTR

With DB2 Server for VSE, the VSAM I/O buffer address normally changes every time it does an I/O, hence will suffer from using FASTTR. It performs I/O directly from its local buffer.

Virtual Addressability Extension (VAE)

While there is a performance advantage to placing the database partition and the CICS partition in the same address space, it is nearly impossible. Instead, place the database partition and the CICS partition in separate address spaces. This will increase the contention between these two partitions and introduce additional overhead for address space switching. However, you will have a significant amount of space for:

• Additional agent structures
• Larger buffer pools
• More locks
• A larger package cache

All of these will improve your server's performance if you have enough main storage to avoid increased paging.

31 Bit Addressing

You can use 31 bit addressing to increase the database partition size above the normal 16MB limit (refer to Storage Above 16MB (31 Bit Addressing)). However, because only one partition in the address space can use storage above the 16MB line, it is still impractical to place CICS and the database partition in one address space. Fortunately, with 31 bit addressing the cost of address space switching becomes a relatively minor performance concern.

Compile Partition Size

Ensure that the partition you intend to use to compile application programs is large enough. Preprocessing tends to produce relatively large source programs, and compiles can take as much as ten times longer than necessary if your partition is too small. Start with a partition size of 1.2MB and expand it if necessary.