Oracle RAC Scalability with WebLogic Server

You can add nodes to the cluster easily and there is no need to partition data when you add them. This means that you can horizontally scale the database tier as usage and demand grows by adding RAC nodes, storage, or both. You can then scale WebLogic Server by adding a connection pool that maps to the new node.

Oracle RAC Availability with WebLogic Server

Note that Oracle RAC does not provide failover for database connections; nor does WebLogic Server. But transactions are failed over in the sense that they are heuristically driven to completion, based on the time of the failure.

数据库连接不提供failover功能，但事务可以被failover。

Oracle RAC Load Balancing with WebLogic Server

If your application requires load balancing across RAC nodes when using global transactions (XA), BEA supports this capability through use of JDBC MultiPools with Oracle RAC nodes.

In a configuration without a MultiPool, WebLogic Server relies on the connect-time failover feature provided by the Oracle Thin driver to work with Oracle RAC. As described in Oracle's Technical Note 235118.1, the Oracle Thin driver cannot guarantee that a transaction is initiated and concluded on the same Oracle RAC instance when the driver is configured for load balancing. As Oracle RAC requires that all database operations inside a global transaction be routed to the same Oracle instance, this known limitation means that you cannot use driver-level load balancing when using XA with Oracle RAC and therefore you cannot use a primary/primary RAC configuration.

不用多池就需要靠Oracle Thin driver来实现failover，但不能负载均衡XA事务。

Oracle RAC Failover with WebLogic Server

Although Oracle RAC offers JDBC connect-time failover features, for most configurations, BEA recommends using WebLogic JDBC MultiPools to handle failover instead.

Note: Transparent Application Failover (TAF) requires the use of the Oracle OCI driver. Because BEA requires the use of the Oracle Thin driver, TAF is not supported.

BEA推荐用WebLogic JDBC多池来实现failover。

Configuring the Listener Process for Each Oracle RAC Instance

For Oracle RAC, the listener process establishes a communication pathway between a user process and an Oracle instance. When you use Oracle RAC with WebLogic Server, the user process is typically a JDBC connection pool.

When a connection pool is created, it attempts to create a pool of database connections for applications to borrow. If a pooled database connection becomes inoperative or if the connection pool is configured to grow in capacity, the connection pool attempts to create additional database connections up to the maximum specified in the configuration file. In all of these instances, the Oracle listener process handles the connection request on the Oracle RAC instance.

为了实现负载均衡，连接池的初始值和最大值不能相同。

Choosing a WebLogic Server Configuration for Use with Oracle RAC

To connect to multiple Oracle 9i RAC or Oracle 10g RAC instances when using global transactions (XA), BEA recommends the use of transaction-aware WebLogic JDBC MultiPools, which support failover and load balancing, to connect to the RAC nodes. For more information see Using MultiPools with Global Transactions. You must either Weblogic Server 8.1 SP5 or later or have WebLogic Server 8.1 SP4 with the Oracle 10g RAC patch installed for this configuration. The WebLogic Server 8.1 SP4 Oracle 10g RAC patch is available at http://dev2dev.bea.com/wlserver/patch/wls81sp4_MP_OracleRAC_patch.html

当用全局事务（XA）时，为了连接到Oracle 9i RAC或者Oracle 10g RAC实例，BEA推荐使用WebLogic JDBC多池进行事务处理，你必须具有Weblogic Server 8.1 SP5或更高版本，或者WebLogic Server 8.1 SP4具有Oracle 10g RAC补丁。

WebLogic Server 8.1 SP5 is certified to support Multipools with XA only on Oracle RAC

WebLogic Server 8.1 SP5被鉴定仅仅在Oracle RAC中可支持具有全局事务的多池

在WebLogic Cluster＋Oracle RAC系统中，需要考虑如下限制：

Required JDBC Driver Configuration for Use with XA

In this configuration, you must use the Oracle Thin driver connect-time failover to create database connections

Oracle 9i RAC XA Requirements

       全局事务必须被初始化、准备、终止在RAC的同一个实例上。

       在RAC中，全局事务必须有相同的事务ID。

在WebLogic Cluster和Oracle RAC的系统中，存在以下潜在风险：

1、 在某些情况下，数据会丢失，如网络中断

2、 在某些特定的情况下，会发生数据死锁。

3、 在某些特定的情况下，事务处理顺序发生变化。

§                        The Oracle Thin Driver 10g and Oracle Thin/XA Driver 10g are the default drivers for WebLogic Platform. 8.1 SP3.

WebLogic Platform. 8.1 SP3默认的驱动是Oracle Thin Driver 10g和Oracle Thin/XA Driver 10g