oracle IO waits

Oracle IO waits refer to the time that a session waits for input/output (IO) operations to complete. When a session needs to access data that is not currently in memory, it must read the data from disk, which can be a slow process. During this time, the session is said to be waiting for IO to complete.

There are several types of IO waits in Oracle, including:

1. DB file sequential read: This occurs when a session is waiting for a single block to be read from disk.

2. DB file scattered read: This occurs when a session is waiting for multiple non-contiguous blocks to be read from disk.

3. Direct path read: This occurs when a session is performing a full table scan and waiting for the data blocks to be read from disk.

4. Direct path write: This occurs when a session is performing a bulk insert or update and waiting for the data blocks to be written to disk.

When a session is waiting for IO to complete, it is important to identify the cause of the wait and address any underlying issues. This may involve optimizing the database design, improving the storage infrastructure, or tuning the database parameters to better balance IO and CPU usage.