Tuning Fast Path systems

Your objective in tuning the IMS online system when Fast Path applications are present depends upon the importance of the message-driven programs and their criteria for acceptable response time.

The performance analysis studies that you should undertake are:

• Examining the availability of sufficient real storage
• Checking the effectiveness of the balancing groups
• Investigating the number of Fast Path dependent regions and the possibility of parallel processing
• Monitoring of the required frequency of DEDB reorganization to reduce fragmented units of work
• Monitoring of the use of DEDB overflow buffers
• Monitoring the forced serialization of programs that concurrently need to use overflow buffers specified by the EXEC statement DBFX parameter
• Examining the area key ranges and whether the randomizing algorithm can be refined
• Reducing the amount of mixed mode processing

Fast Path performance can also be improved by eliminating unnecessary delays caused by the following:

• Transaction volume to a particular Fast Path application program
• DEDB structure considerations
• Contention for DEDB Control Interval (CI) resources
• Exhaustion of DEDB DASD space
• Utilization of available real storage
• Sync point processing and physical logging
• Contention for output threads (OTHR)
• Overhead resulting from reprocessing
• Dispatching priority of processor-dominant and I/O-dominant tasks
• DASD contention caused by I/O on DEDBs
• Resource locking considerations with block level sharing
• Buffer pool usage and not grouping Fast Path application programs with similar buffer use characteristics together into one or more message classes

Statistics on transaction processing and contention for CIs can be obtained from the output of the Fast Path Log Analysis utility (DBFULTA0), which retrieves (from system log input) data relating to the usage of Fast Path resources.