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SAP Sybase SQL Anywhere 16.0 » SQL Anywhere Server - Database Administration » High availability and read-only scale-out systems » Database mirroring » Setting up a database mirroring system » How the primary server is chosen by database mirroring system


Preferred database server in a database mirroring system

In a database mirroring system, you can specify one partner server as the preferred server. The preferred server is the partner that by default runs as the primary server and has ownership of the database.

If the preferred server becomes unavailable, then the server that was acting as the mirror server becomes the primary server. When the preferred server restarts it:

  1. Obtains any transaction log entries it does not already have from the current primary server.

  2. Asks the current primary server to relinquish ownership of the database. The servers then switch roles. The preferred server becomes the primary server and the other server becomes the mirror server. Any connections to the database on the non-preferred server are lost when the database ownership changes.

You specify a preferred server by adding PREFERRED='YES' to the CREATE MIRROR SERVER statement that defines the partner server.

 See also