Relative ratio of I/O speed

This value indicates the ratio between the I/O rate of the federated server and the I/O rate of the server on which the remote data source is located.

This value is defined as the I/O rate for the federated server divided by the I/O rate for the remote server. For example, if the I/O rate for the federated server is twice the I/O rate for the remote server, then IO_RATIO should be set to 2. But if the I/O rate for the federated server is half that of the remote server, then IO_RATIO should be set to 0.5.

When you do not set the I/O ratio server option explicitly, the federated optimizer uses a default value of 1, which indicates that the I/O rates of both the federated and remote servers are equal.

A low IO_RATIO of less than one indicates that the remote server has a higher I/O rate than the federated server. In this case, the optimizer will tend to favor pushing down I/O-intensive operations to the remote data source. A low ratio is a value that is less than 1.