This section explains how to tune the number of processes in asynchronous READ processing specified in the pd_max_ard_process operand. When the asynchronous READ facility is used, if the number of processes in asynchronous READ processing is low and the number of SQL statements to which the asynchronous READ facility is applicable is high, processing time can increase due to completion waiting during I/O processing of asynchronous READ processes.
- Information to be referenced
- Reference the following information in the UAP statistical report (for details about UAP statistical reports, see the manual HiRDB Version 8 UAP Development Guide):
- Accumulated synchronization wait time during asynchronous READ (ARWT, ARWTM)
- Accumulated database I/O time (IOTIM, IOTIMM)
- Average synchronization wait time during asynchronous READ (ARWTA, ARWTMA)
- Average synchronization I/O time during asynchronous READ (ARSTA, ARSTMA)
- Purpose
- The purpose is to determine the number of appropriate processes for asynchronous READ, when the asynchronous READ facility is not effective.
- Evaluating the analysis results
- Compare with the following times; if step 2 is longer, consider that the asynchronous wait time may be too long:
- Accumulated database I/O time (IOTIM, IOTIMM) when the asynchronous READ facility is not used
- Total of the average synchronization wait time during asynchronous READ (ARWTA, ARWTMA) and accumulated database I/O time (IOTIM, IOTIMM) when the asynchronous READ facility is used
- Compare the following times; if step 2 is longer, consider that the asynchronous wait time may be too long:
- Average synchronization I/O time during asynchronous READ (ARSTA, ARSTMA) when the asynchronous READ facility is used
- Average synchronization wait time during asynchronous READ (ARWTA, ARWTMA) when the asynchronous READ facility is used
- The number of asynchronous READs (AIO-R) can be understood from the statistical information for HiRDB files related to database operations obtained by the statistics analysis utility.
- Actions to be taken
- If the accumulated synchronization wait time during asynchronous READ (ARWT, ARWTM) or the average synchronization wait time (ARWTA, ARWTMA) during asynchronous READ is long, increase the value of the pd_max_ard_process operand.
- However, if the result of checking the number of asynchronous READs (AIO-R) is that the asynchronous READ requests are concentrated in the same RDAREA, increasing the value of this operand will have no effect. In such a case, have the RDAREA be composed of multiple HiRDB files, and place each HiRDB file on a different disk.
- For the maximum effective value of the pd_max_ard_process operand, of the RDAREAs for which the number of asynchronous READ (AIO-R) is specified, specify the number that simultaneously executes the prefetch facility. If the number of processes increases, it is necessary to consider the system resources (shared memory and message queues).
- If the accumulated synchronization wait time during asynchronous READ (ARWT, ARWTM) or the average synchronization wait time during asynchronous READ (ARWTA, ARWTMA) is short, the asynchronous READ facility cannot provide greater effectiveness.