Configuring Connection Failover
Connection failover allows an application to connect to an alternate, or backup, database server if the primary database server is unavailable, for example, because of a hardware failure or traffic overload.
See Using Connection Failover for more information about connection failover.
To configure connection failover to another server, you must specify a list of alternate database servers that are tried at connection time if the primary server is not accepting connections. To do this, use the Alternate Servers connection string option. Connection attempts continue until a connection is successfully established or until all the databases in the list have been tried once (the default).
Optionally, you can specify the following additional connection failover features:
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The number of times the data provider attempts to connect to the primary and alternate servers after the initial connection attempt. By default, the data provider does not retry. To set this feature, use the Connection Retry Count connection string option.
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The wait interval, in seconds, used between attempts to connect to the primary and alternate servers. The default interval is 3 seconds. To set this feature, use the Connection Retry Delay connection option.
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Whether the data provider will use load balancing in its attempts to connect to primary and alternate servers. If load balancing is enabled, the data provider uses a random pattern instead of a sequential pattern in its attempts to connect. The default value is not to use load balancing. To set this feature, use the Load Balancing connection string option.
You use a connection string to direct the data provider to use connection failover. See Using Connection Strings.
The following C# code fragment includes a connection string that configures the data provider to use connection failover in conjunction with all of its optional features – load balancing, connection retry, and connection retry delay:
Conn = new PsqlConnection Conn = new PsqlConnection();
Conn = new PsqlConnection("Host=myServer;User ID=test;Password=secret;
Server DSN=SERVERDEMO;Alternate Servers="Host=AcctServer, Host=AcctServer2";
Connection Retry Count=4;Connection Retry Delay=5;Load Balancing=true;
Connection Timeout=60")
Specifically, this connection string configures the data provider to use two alternate servers as connection failover servers, to attempt to connect four additional times if the initial attempt fails, to wait five seconds between attempts, and to try the primary and alternate servers in a random order. Each connection attempt lasts for 60 seconds, and uses the same random order that was established on the first retry.