This illustration shows asynchronous network I/O in a two-site Data Guard configuration. On the primary site in this configuration, the LGWR process deploys a network server process to initiate network I/O operations on the primary database. This illustration shows one network server process on the network connection to an asynchronous standby database. The network server process is shown sending write requests to the RFS process on the standby database, and receiving replies from the RFS process. Also shown on the primary site in this figure, the network server process is caching online redo logs in the network buffer.

On the standby site in this illustration, the RFS process is shown doing two-way communication with the standby redo logs.

The following text describes more about asynchronous network I/O and the processes depicted in this illustration.