IO_COMPLETION Wait Type

IO_COMPLETION Wait Type 用于非数据页IO的IO操作上，非数据页IO的IO操作是操作非数据页的IO操作，like a transaction log restore operation or the reading of bitmap pages, like the GAM page.

IO_COMPLETION reports on non-data pages and essentially is a SQL Server thread awaiting the kernel to return the IO request status.

IO_COMPLETION Used to indicate a wait for I/O for operation (typically synchronous) like sorts and various situations where the engine needs to do a synchronous I/O

If wait times are high then you have a disk I/O bottleneck. The problem will be determining what type of operation and where the bottleneck exists. For sorts, it is on the storage system associated with tempdb. Note that database page I/O does not use this wait type. Instead look at PAGEIOLATCH waits.

Occurs while waiting for I/O operations to complete. This wait type generally represents non-data page I/Os.

Data page I/O completion waits appear as PAGEIOLATCH_* waits.

Waits on this wait type can result from inefficient SQL statements. Tuning the SQL statement will allow it to execute while reading less data, which will reduce wait times on this event.





参考文档：
http://blog.sqlauthority.com/2011/02/10/sql-server-io_completion-wait-type-day-10-of-28/ https://support.microsoft.com/en-us/kb/822101