“I/O Device Contention” reports the number of times a task was put to sleep while waiting for a semaphore for a particular device.
When a task needs to perform physical I/O, Adaptive Server fills out the I/O structure and links it to a per-engine I/O queue. If two Adaptive Server engines request an I/O structure from the same device at the same time, one of them sleeps while it waits for the semaphore.
If there is significant contention for I/O device semaphores, try reducing it by redistributing the tables across devices or by adding devices and moving tables and indexes to them.
See “Spreading data across disks to avoid I/O contention” on page 93 in Performance and Tuning: Basics for more information.
