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OCI8 Connection Handling and Connection PoolingConnection FunctionsThe OCI8 extension provides three different functions for connecting to Oracle. The standard connection function is oci_connect. This creates a connection to an Oracle database and returns a resource used by subsequent database calls. Connecting to an Oracle server is a reasonably expensive operation in terms of the time that it takes to complete. The oci_pconnect function uses a persistent cache of connections that can be re-used across different script requests. This means that the connection overhead will typically only occur once per PHP process (or Apache child). If the application connects to Oracle using a different set of database credentials for each web user, the persistent cache employed by oci_pconnect will become less useful as the number of concurrent users increases, to the point where it may start to adversely affect the overall performance of the Oracle server due to maintaining too many idle connections. If the application is structured in this way, it is recommended to either tune the application using the oci8.max_persistent and oci8.persistent_timeout configuration settings (these will give control over the persistent connection cache size and lifetime), use Oracle Database Resident Connection Pooling (in Oracle Database 11g or later), or use oci_connect instead. Both oci_connect and oci_pconnect employ a connection cache; if multiple calls to oci_connect use the same parameters in a given script, the second and subsequent calls return the existing connection handle. The cache used by oci_connect is cleaned up at the end of the script run, or when the connection handle is explicitly closed. The function oci_pconnect has similar behavior, although its cache is maintained separately and survives between HTTP requests. This caching feature means the two handles are not transactionally isolated (they are in fact the same connection handle, so there is no isolation of any kind). If the application needs two separate, transactionally isolated connections, then use oci_new_connect. The oci_pconnect cache is cleared and any database connections closed when the PHP process terminates, so effective use of persistent connections requires that PHP be an Apache module or used with FPM, or similar. Persistent connections will not have any benefits over oci_connect when PHP is used with CGI or via the command-line. The function oci_new_connect always creates a new connection to the Oracle server, regardless of what other connections might already exist. High traffic web applications should avoid using oci_new_connect, especially in the busiest sections of the application. Persistent connections can be closed by the user, allowing greater control over connection resource usage. Persistent connections will now also be closed automatically when there is no PHP variable referencing them, such as at the end of scope of a PHP user function. This will rollback any uncommitted transaction. These changes to persistent connections make them behave similarly to non-persistent connections, simplifying the interface, allowing for greater application consistency and predictability. Use oci8.old_oci_close_semantics set to On to retain the historical behavior.
The automatic re-establishment of PHP persistent connections after an Apache
or FPM process respawns means Oracle Database DRCP Connection PoolingPHP supports Oracle Database Resident Connection Pooling (DRCP). DRCP allows more efficient use of database machine memory and provides high scalability. No, or minimal, application changes are needed to use DRCP.
DRCP is suited for applications that connect using few database
schemas and hold database connections open for a short period of
time. Other applications should use Oracle's
default DRCP benefits all three connection functions, but gives the highest scalability when connections are created with oci_pconnect. For DRCP to be available in OCI8, Oracle client libraries used by PHP and the version of the Oracle Database must both be 11g or greater. Documentation on DRCP is found in several Oracle manuals. For example, see » Configuring Database Resident Connection Pooling in the Oracle documentation for usage information. A » DRCP white paper contains background information on DRCP. To use DRCP, install the OCI8 extension and Oracle 11g (or later) libraries and then follow these steps:
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