Summary information |
|
|---|---|
Default value |
10 |
Range of values |
1–2147483647 |
Status |
Dynamic |
Display level |
Comprehensive |
Required role |
System Administrator |
i/o polling process count specifies the maximum number of processes that can be run by Adaptive Server before the scheduler checks for disk and/or network I/O completions. Tuning i/o polling process count affects both the response time and throughput of Adaptive Server.
Adaptive Server checks for disk or network I/O completions:
If the number of tasks run since the last time Adaptive Server checked for I/O completions equals the value for i/o polling process count, and
At every Adaptive Server clock tick.
As a general rule, increasing the value of i/o polling process count may increase throughput for applications that generate a lot of disk and network I/O. Conversely, decreasing the value may improve process response time in these applications, possibly at the risk of lowering throughput.
If your applications create both I/O and CPU-bound tasks, tuning i/o polling process count to a low value (1–2) ensures that I/O-bound tasks get access to CPU cycles.
For OLTP applications (or any I/O-bound application with user connections and short transactions), tuning i/o polling process count to a value in the range of 20–30 may increase throughput, but it may also increase response time.
When tuning i/o polling process count, consider three other parameters:
sql server clock tick length, which specifies the duration of Adaptive Server’s clock tick in microseconds. See “sql server clock tick length”.
time slice, which specifies the number of clock ticks Adaptive Server’s scheduler allows a user process to run. See “time slice”.
cpu grace time, which specifies the maximum amount of time (in clock ticks) a user process can run without yielding the CPU before Adaptive Server preempts it and terminates it with a time-slice error. See “cpu grace time”.
Use sp_sysmon to determine the effect of changing the i/o polling process count parameter. See the Performance and Tuning Guide for more information.
