UCP and RAC

If you configure a Gridlink Datasource with the wrong ServiceName, you might get:

java.sql.SQLException: Pool connect failed : java.lang.ClassCastException: java.lang.Boolean cannot be cast to oracle.ucp.jdbc.oracle.OracleConnectionAffinityContext

This is possibly one of the weirdest exceptions I have ever seen...spooky and unreal...
It turns out that the root cause could also be that tablespace is full, or other DB-related issues.... but it's NOT a WLS or Application issue (apart from being a useless error message...)

If you wonder what the "ucp" means, it's a RAC-specific implementation of the more traditional connection pool : https://docs.oracle.com/cd/E11882_01/java.112/e12265/intro.htm#BABDIDGD

The way I understand it is that a UCP is a RAC-specific Connection Pool service running UNDER the WebLogic connection pool, and handling RAC-specific features like seamless recovery from node failures.

PS the whole stacktrace is:

Caused By: java.sql.SQLException: java.lang.ClassCastException: java.lang.Boolean cannot be cast to oracle.ucp.jdbc.oracle.OracleConnectionAffinityContext
        at weblogic.jdbc.common.internal.JDBCUtil.wrapAndThrowResourceException(JDBCUtil.java:278)
        at weblogic.jdbc.common.internal.RmiDataSource.getPoolConnection(RmiDataSource.java:503)
        at weblogic.jdbc.common.internal.RmiDataSource.getConnectionInternal(RmiDataSource.java:594)
        at weblogic.jdbc.common.internal.RmiDataSource.getConnection(RmiDataSource.java:545)
        at weblogic.jdbc.common.internal.RmiDataSource.getConnection(RmiDataSource.java:538)
        Truncated. see log file for complete stacktrace
Caused By: java.lang.ClassCastException: java.lang.Boolean cannot be cast to oracle.ucp.jdbc.oracle.OracleConnectionAffinityContext
        at oracle.ucp.jdbc.oracle.RACManagerImpl.selectConnectionPerRCLBAndAffinity(RACManagerImpl.java:2126)
        at weblogic.jdbc.common.rac.internal.UCPRACModuleImpl.getConnection(UCPRACModuleImpl.java:269)
        at weblogic.jdbc.common.internal.HAConnectionPool.reserve(HAConnectionPool.java:264)
        at weblogic.jdbc.common.internal.ConnectionPoolManager.reserve(ConnectionPoolManager.java:137)
        at weblogic.jdbc.common.internal.RmiDataSource.getPoolConnection(RmiDataSource.java:501)
        Truncated. see log file for complete stacktrace