By Steve Felts on Oct 15, 2012
So far, I have covered Client Identity and Oracle Proxy Session features, with WLS or database credentials. This article will cover one more feature, Identify-based pooling. Then, there is one more topic to cover - how these options play with transactions.Identity-based Connection Pooling
An identity based pool creates a heterogeneous pool of connections. This allows applications to use a JDBC connection with a specific DBMS credential by pooling physical connections with different DBMS credentials. The DBMS credential is based on either the WebLogic user mapped to a database user or the database user directly, based on the “use database credentials” setting as described earlier. Using this feature enabled with “use database credentials” enabled seems to be what is proposed in the JDBC standard, basically a heterogeneous pool with users specified by getConnection(user, password).
The allocation of connections is more complex if Enable Identity Based Connection Pooling attribute is enabled on the data source. When an application requests a database connection, the WebLogic Server instance selects an existing physical connection or creates a new physical connection with requested DBMS identity.
The following section provides information on how heterogeneous connections are created:
1. At connection pool initialization, the physical JDBC connections based on the configured or default “initial capacity” are created with the configured default DBMS credential of the data source.
2. An application tries to get a connection from a data source.
3a. If “use database credentials” is not enabled, the user specified in getConnection is mapped to a DBMS credential, as described earlier. If the credential map doesn’t have a matching user, the default DBMS credential is used from the datasource descriptor.
3b. If “use database credentials” is enabled, the user and password specified in getConnection are used directly.
4. The connection pool is searched for a connection with a matching DBMS credential.
5. If a match is found, the connection is reserved and returned to the application.
6. If no match is found, a connection is created or reused based on the maximum capacity of the pool:
- If the maximum capacity has not been reached, a new connection is created with the DBMS credential, reserved, and returned to the application.
- If the pool has reached maximum capacity, based on the least recently used (LRU) algorithm, a physical connection is selected from the pool and destroyed. A new connection is created with the DBMS credential, reserved, and returned to the application.
It should be clear that finding a matching connection is more expensive than a homogeneous pool. Destroying a connection and getting a new one is very expensive. If you can use a normal homogeneous pool or one of the light-weight options (client identity or an Oracle proxy connection), those should be used instead of identity based pooling.
Regardless of how physical connections are created, each physical connection in the pool has its own DBMS credential information maintained by the pool. Once a physical connection is reserved by the pool, it does not change its DBMS credential even if the current thread changes its WebLogic user credential and continues to use the same connection.
To configure this feature, select Enable Identity Based Connection Pooling. See http://docs.oracle.com/cd/E24329_01/apirefs.1211/e24401/taskhelp/jdbc/jdbc_datasources/EnableIdentityBasedConnectionPooling.html "Enable identity-based connection pooling for a JDBC data source" in Oracle WebLogic Server Administration Console Help.
You must make the following changes to use Logging Last Resource (LLR) transaction optimization with Identity-based Pooling to get around the problem that multiple users will be accessing the associated transaction table.
- You must configure a custom schema for LLR using a fully qualified LLR table name. All LLR connections will then use the named schema rather than the default schema when accessing the LLR transaction table.
- Use database specific administration tools to grant permission to access the named LLR table to all users that could access this table via a global transaction. By default, the LLR table is created during boot by the user configured for the connection in the data source. In most cases, the database will only allow access to this user and not allow access to mapped users.
Connections within Transactions
Now that we have covered the behavior of all of these various options, it’s time to discuss the exception to all of the rules. When you get a connection within a transaction, it is associated with the transaction context on a particular WLS instance.
When getting a connection with a data source configured with non-XA LLR or 1PC (using the JTS driver) with global transactions, the first connection obtained within the transaction is returned on subsequent connection requests regardless of the values of username/password specified and independent of the associated proxy user session, if any. The connection must be shared among all users of the connection when using LLR or 1PC.
For XA data sources, the first connection obtained within the global transaction is returned on subsequent connection requests within the application server, regardless of the values of username/password specified and independent of the associated proxy user session, if any. The connection must be shared among all users of the connection within a global transaction within the application server/JVM.