This section explains the procedure for tuning the number of asynchronous READ processes specified in the pd_max_ard_process operand. When the asynchronous READ facility is used, HiRDB might wait for the completion of I/O operations for asynchronous READ processes. This occurs if the number of asynchronous READ processes is small, and if the asynchronous READ facility is applied to multiple SQL statements concurrently. As a result, processing might take longer.

Information to be referenced

Reference the following information in the UAP statistical report (for details about UAP statistical reports, see the HiRDB Version 9 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

To determine how appropriate the number of asynchronous READ processes is when the asynchronous READ facility has no effect.

Evaluating the analysis results

Compare with the following times; if step 2 is longer, consider that the asynchronous wait time might be too long:

1. Accumulated database I/O time (IOTIM, IOTIMM) when the asynchronous READ facility is not used
2. 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 might be too long:

1. Average synchronization I/O time during asynchronous READ (ARSTA, ARSTMA) when the asynchronous READ facility is used
2. 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. When you increase the number of asynchronous READ processes, you must take the system resources (shared memory and message queue) into consideration.

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.