I/O Device Contention

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.

Device contention occurs only when you have enabled disk mirroring (the default is “disabled”) or when I/Os are delayed. For more information about delayed I/Os, see “Disk I/O Management”.

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.