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SAP Sybase SQL Anywhere 16.0 » SQL Anywhere Server - Database Administration » High availability and read-only scale-out systems » SQL Anywhere read-only scale-out

 

Connecting to a database in a read-only scale-out system

To set up a scale-out system, it is recommended that you create two definitions with the CREATE MIRROR SERVER statement for the database server that is acting as the root node:

  • one definition for the partner role

    In a scale-out system, you must define one partner server. The name that is specified in the partner server definition is used in connection strings and when starting the database server.

  • one definition for the primary role.

    The database server defined as the primary server is the default parent for copy nodes in the scale-out system. If there is no primary server defined, then you must specify the parent for each copy node that is added to the system.

When you use read-only scale-out, it is recommended that the application connects to the root database server, and the root database server uses information from the application's connection string, together with status and load information from the copy nodes, to determine which node the application should connect to. You can choose to have the application connect to the copy node that is least heavily loaded using the NodeType=COPY connection parameter. Specifying this causes the root database server to redirect the client to that node. See Connect to copy nodes.

If an application makes and drops several such connections within a short period of time, the connection is pooled and the root database server is not asked which copy node to use. This behavior reduces the load on the root database server, but may not give expected behavior. The application can specify that its connections are not to be pooled to ensure that the root server determines which copy node to connect to on each connection. See Connection pooling and read-only scale-out.

Tip

Check the status of the database servers in a scale-out system by monitoring the primary database using the SQL Anywhere Monitor.

You can also monitor a scale-out system from Sybase Central by connecting to the primary database and checking the status of the database servers in the Health And Statistics pane.

 See also

Connect to copy nodes

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