I/O priorities
The database server prioritizes disk I/O by assigning different types of I/O to different classes of virtual processors and by assigning priorities to the nonlogging I/O queues.
Prioritizing ensures that a high-priority log I/O, for example,
is never queued behind a write to a temporary file, which has a low
priority. The database server prioritizes the different types of disk
I/O that it performs, as the table shows.
| Priority | Type of I/O | VP class |
|---|---|---|
| 1st | Logical-log I/O | CPU or LIO |
| 2nd | Physical-log I/O | CPU or PIO |
| 3rd | Database I/O | CPU or AIO |
| 3rd | Page-cleaning I/O | CPU or AIO |
| 3rd | Read-ahead I/O | CPU or AIO |