DB2 Version 10.1 for Linux, UNIX, and Windows

Java client support for high availability for connections to DB2 for Linux, UNIX, and Windows servers

DB2® for Linux, UNIX, and Windows servers provide high availability for client applications, through workload balancing and automatic client reroute. This support is available for applications that use Java™ clients (JDBC, SQLJ, or pureQuery®), as well as non-Java clients (ODBC, CLI, .NET, OLE DB, PHP, Ruby, or embedded SQL).

For Java clients, high availability support requires IBM® Data Server Driver for JDBC and SQLJ version 3.58 or 4.8, or later.

High availability support for connections to DB2 for Linux, UNIX, and Windows servers includes:

Automatic client reroute

This support enables a client to recover from a failure by attempting to reconnect to the database through an alternate server. Reconnection to another server is called failover. For Java clients, automatic client reroute support is always enabled.

Automatic client reroute capability for Java applications is available with IBM Data Server Driver for JDBC and SQLJ type 4 connectivity or IBM Data Server Driver for JDBC and SQLJ type 2 connectivity.

Servers can provide automatic client reroute capability in any of the following ways:

Several servers are configured in a DB2 pureScale® instance. A connection to a database is a connection to a member of that DB2 pureScale instance. Failover involves reconnection to another member of the DB2 pureScale instance. This environment requires that clients use TCP/IP to connect to the DB2 pureScale instance.
A DB2 pureScale instance and an alternate server are defined for a database. Failover first involves reconnection to another member of the DB2 pureScale instance. Failover to the alternate server is attempted only if no member of the DB2 pureScale instance is available.
A DB2 pureScale instance is defined for the primary server, and another DB2 pureScale instance is defined for the alternate server. Failover first involves reconnection to another member of the primary DB2 pureScale instance. Failover to the alternate DB2 pureScale instance is attempted only if no member of the primary DB2 pureScale instance is available.
A database is defined on a single server. The configuration for that database includes specification of an alternate server. Failover involves reconnection to the alternate server.

For Java, client applications, failover for automatic client reroute can be seamless or non-seamless. With non-seamless failover, when the client application reconnects to another server, an error is always returned to the application, to indicate that failover (connection to the alternate server) occurred. With seamless failover, the driver does not return an error if a connection failure and successful reconnection to an alternate server occur during execution of the first SQL statement in a transaction.

In a DB2 pureScale instance, automatic client reroute support can be used without workload balancing or with workload balancing.

You can configure automatic client reroute to include the following additional capability:

Client affinities: Client affinities is an automatic client reroute solution that is controlled completely by the client. It is intended for situations in which you need to connect to a particular primary server. If an outage occurs during the connection to the primary server, you use client affinities to enforce a specific order for failover to alternate servers.

Workload balancing

Workload balancing can improve availability of a DB2 pureScale instance.

With workload balancing, a DB2 pureScale instance ensures that work is distributed efficiently among members.

Workload balancing for Java applications is available with IBM Data Server Driver for JDBC and SQLJ type 4 connectivity only.

Java clients on any operating system support workload balancing. The connection from the client to the DB2 pureScale instance must use TCP/IP.

When workload balancing is enabled, the client gets frequent status information about the members of the DB2 pureScale instance through a server list. The client caches the server list and uses the information in it to determine the member to which the next transaction should be routed.

For Java applications, when JNDI is used, the cached server list can be shared by multiple JVMs for the first connection. However workload balancing is always performed within the context of a single JVM.

DB2 for Linux, UNIX, and Windows supports two types of workload balancing:

Connection-level workload balancing: Connection-level workload balancing is performed at connection boundaries. It is not supported for Java clients.
Transaction-level workload balancing: Transaction-level workload balancing is performed at transaction boundaries. Client support for transaction-level workload balancing is disabled by default for clients that connect to DB2 for Linux, UNIX, and Windows.