OCISessionGet is the recommended uniform function call to retrieve a session. Another interface can be used if the application needs to set any special attributes on the user session handle and server handle. For such a requirement, applications need to allocate all the handles connection pool handle, server handles, session handles and service context handles. Connection pooling does the multiplexing of a virtual server handle over physical connections transparently, hence eliminating the need for users to do so.
The user gets the feeling of a session having a dedicated virtual connection. Since the multiplexing is done transparently to the user, Users should not attempt to multiplex sessions over the virtual server handles themselves. The concepts of session migration and session switching, which require explicit multiplexing at the user level, are defunct in the case of connection pooling and should not be used. There should be a one-to-one mapping between virtual server handles and sessions.
The memory tuning requirements for the back-end database will be similar to configuring the LARGE POOL in case of a shared server back end except that the instance is still in dedicated mode.
The application must avoid using dedicated database links on the back end with connection pooling. If the back end is a dedicated server, effective connection pooling will not be possible because sessions using dedicated database links will be tied to a physical connection rendering that same connection unusable by other sessions.
If your application uses dedicated database links and you do not see effective sharing of back-end processes among your sessions, you must consider using shared database links. Corresponding to the logon calls, these are the interfaces to use to log off from the database in connection pooling mode. Examples of connection pooling in tested complete programs can be found in c democp.
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Session pooling means that the application will create and maintain a group of stateless sessions to the database. These sessions will be handed over to thin clients as requested. If no sessions are available, a new one may be created. When the client is done with the session, the client will release it to the pool. Thus, the number of sessions in the pool can increase dynamically. Some of the sessions in the pool may be 'tagged' with certain properties. For instance, a user may request for a default session, set certain attributes on it, then label it or 'tag' it and return in to the pool.
That user, or some other user, can require a session with the same attributes, and thus request for a session with the same tag. There may be several sessions in the pool with the same tag. The 'tag' on a session can be changed or reset. The behavior of the application when no free sessions are available and the pool has reached it's maximum size, will depend on certain attributes. A new session may be created or an error returned, or the thread may just block and wait for a session to become free. The main benefit of this type of pooling will be performance.
Making a connection to the database is a time-consuming activity, especially when the database is remote. Thus, instead of a client spending time connecting to the server, authenticating its credentials, and then receiving a valid session, it can just pick one from the pool. Provide an interface for the application to create a pool and specify the minimum, increment and maximum number of sessions in the pool.
Provide an interface for the user to obtain and release a default or 'tagged' session to the pool. A 'tagged' session is one with certain client-defined properties.
- OCI Programming Advanced Topics.
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Allow the application to dynamically change the number of minimum and maximum number of sessions. Provide a mechanism to always maintain an optimum number of open sessions, by closing sessions that have been idle for very long, and creating sessions when required.
A session pool can be either homogeneous or heterogeneous. Homogeneous session pooling means that sessions in the pool are alike with respect to authentication have the same user name and password and privileges. Heterogeneous session pooling means that you must provide authentication information because the sessions can have different security attributes and privileges. The tags provide a way for users to customize sessions in the pool. A client may get a default or untagged session from a pool, set certain attributes on the session such as NLS settings , and return the session to the pool, labeling it with an appropriate tag in the OCISessionRelease call.
The user, or some other user, may request a session with the same tags in order to have a session withe the same attributes, and can do so by providing the same tag in the OCISessionGet call. This is the session pool handle. This is the authentication information handle. It supports all the attributes that are supported for user session handle.
Please refer to user session handle attributes for more information. The steps in writing a simple session pooling application which uses a user name and password are:. Multiple session pools can be created for an environment handle.
Refer to the function for a discussion of the other modes. For a single session pool, here is an allocation example:. Here is an example of how to use this call:. However, it does not give the user the option of using tagging. Here is an example of how OCILogon2 can be used to log on to the database in session pooling mode:. It gives the user the option of using tagging to label sessions in the pool, and thus make it easier to retrieve specific sessions.
It is taken from cdemosp. Corresponding to the preceding logon calls, these are the interfaces to use to log off from the database in session pooling mode. Here is an example of how this call can be made:. OCIHandleFree must be called to free the session pool handle. Here is how this call can be made:. If database sessions are not reusable by mid-tier threads that is, they are statefull and the number of back-end server processes may cause scaling problems on the database, use OCI connection pooling. If database sessions are reusable by mid-tier threads that is, they are stateless and the number of back-end server processes may cause scaling problems on the database, use OCI session pooling.
If database sessions are not reusable by mid-tier threads that is, they are statefull and the number of back-end server processes will never be large enough to potentially cause any scaling issue on the database, there is no need to use any pooling mechanism. In connection pooling, the pool element is a connection and in session pooling, the pool element is a session.
As with any pool, the pooled resource is locked by the application thread for a certain duration until the thread has done its job on the database and the resource is released. The resource is unavailable to other threads during its period of use.
Hence, application developers need to be aware that any kind of pooling works effectively with relatively short tasks. If the application is performing a long running transaction for example, it may deny the pooled resource to other sharers for long periods of time leading to starvation.
Hence, pooling should be used in conjunction with short tasks and the size of the pool should be sufficiently large to maintain the desired concurrency of transactions. Connections to the database are pooled. Sessions are created and destroyed by the user. Each call to the database will pick up an appropriate available connection from the pool. The application is multiplexing several sessions over fewer physical connections to the database.
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The users can tune the pool configuration to achieve required concurrency. The life-time of the application sessions is independent of the life-time of the cached pooled connections. Sessions and connections are pooled by OCI. The application gets sessions from the pool and release sessions back to the pool.
This is the simplest way to get an OCI Session. The advantage is ease of obtaining an OCI service context. The disadvantage is that you cannot perform any advance OCI operations like session migration, proxy authentication, using a connection pool, or a session pool. This includes the functionality of OCILogon to get a session.
This session may be a new one with a new underlying connection, or one that is started over a virtual connection from an existing connection pool, or one from an existing session pool.