Connection pooling
Using connection pools...
- Alleviates connection management overhead
- Decreases development tasks for data access
Each time an application attempts to access a backend store (such as a database), it requires resources to create, maintain, and release a connection to that datastore. To mitigate the strain this process can place on overall application resources, the appserver enables administrators to establish a pool of backend connections that applications can share on an appserver. Connection pooling spreads the connection overhead across several user requests, thereby conserving application resources for future requests.
The appserver supports JDBC 4.0 APIs for connection pooling and connection reuse. The connection pool is used to direct JDBC calls within the application, as well as for enterprise beans using the database.
Benefits of connection pooling
Connection pooling can improve the response time of any application that requires connections, especially Web-based applications. When a user makes a request over the Web to a resource, the resource accesses a data source. Because users connect and disconnect frequently with applications on the Internet, the application requests for data access can surge to considerable volume. Consequently, the total datastore overhead quickly becomes high for Web-based applications, and performance deteriorates. When connection pooling capabilities are used, however, Web apps can realize performance improvements of up to 20 times the normal results.
With connection pooling, most user requests do not incur the overhead of creating a new connection because the data source can locate and use an existing connection from the pool of connections. When the request is satisfied and the response is returned to the user, the resource returns the connection to the connection pool for reuse. The overhead of a disconnection is avoided. Each user request incurs a fraction of the cost for connecting or disconnecting. After the initial resources are used to produce the connections in the pool, additional overhead is insignificant because the existing connections are reused.
When to use connection pooling
Use connection pooling in an application that meets any of the following criteria:
- It cannot tolerate the overhead of obtaining and releasing connections whenever a connection is used.
- It requires JTA transactions within the appserver.
- It needs to share connections among multiple users within the same transaction.
- It needs to take advantage of product features for managing local transactions within the appserver.
- It does not manage the pooling of its own connections.
- It does not manage the specifics of creating a connection, such as the database name, user name, or password
Avoid trouble: Connection pooling is not supported in an application client. The application client calls the database directly and does not go through a data source.
To use the getConnection() request from the application client, configure the JDBC provider in the application client deployment descriptors, using Rational Application Developer or an assembly tool. The connection is established between application client and the database. Application clients do not have a connection pool, but we can configure JDBC provider settings in the client deployment descriptors.
How connections are pooled together
When you configure a unique data source or connection factory, give it a unique JNDI name. This JNDI name, along with its configuration information, is used to create the connection pool. A separate connection pool exists for each configured data source or connection factory.
Furthermore, the appserver creates a separate instance of the connection pool in each appserver that uses the data source or connection factory. For example:
- If we run a three server cluster in which all of the servers use myDataSource, and myDataSource has a Maximum Connections setting of 10, then we can generate up to 30 connections (three servers times 10 connections).
Other considerations for determining the maximum connections setting:
- Each entity bean transaction requires an additional database connection, dedicated to handling the transaction.
- If clones are used, one data pool exists for each clone.
- AIX, HP-UX, and Solaris, a separate DB2 process is created for each connection; these processes quickly affect performance on systems with low memory and cause errors.
When using connection sharing, it is only possible to share connections obtained from the same connection pool.
Subtopics
Connection and connection pool statistics
Related concepts
Data sources
Unshareable and shareable connections
Transaction type and connection behavior
Related tasks
Tuning connection pools
Set connection factories for resource adapters within applications
Set Java EE Connector connection factories in the admin console
Change connection pool settings with wsadmin
Related
Tuning the application serving environment