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333 lines
12 KiB
XML
333 lines
12 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<chapter xml:id="oci8.connection" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>OCI8 Connection Handling and Connection Pooling</title>
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<section>
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<title>Connection Functions</title>
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<para>
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The OCI8 extension provides three different functions for
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connecting to Oracle. The standard connection function
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is <function>oci_connect</function>. This creates a connection to
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an Oracle database and returns a resource used by subsequent
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database calls.
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</para>
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<para>
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Connecting to an Oracle server is a reasonably expensive operation
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in terms of the time that it takes to complete.
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The <function>oci_pconnect</function> function uses a persistent
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cache of connections that can be re-used across different script
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requests. This means that the connection overhead will typically
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only occur once per PHP process (or Apache child).
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</para>
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<para>
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If the application connects to Oracle using a different set of
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credentials for each web user, the persistent cache employed by
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<function>oci_pconnect</function> will become less useful as the
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number of concurrent users increases, to the point where it may
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start to adversely affect the overall performance of the Oracle
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server due to maintaining too many idle connections. If the
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application is structured in this way, it is recommended to either
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tune the application using
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the <link linkend="ini.oci8.max-persistent">oci8.max_persistent</link>
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and <link linkend="ini.oci8.persistent-timeout">oci8.persistent_timeout</link>
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configuration settings (these will give control over the persistent
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connection cache size and lifetime), use Oracle Database
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Resident Connection Pooling (in Oracle Database 11g or later), or use
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<function>oci_connect</function> instead.
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</para>
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<para>
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Both <function>oci_connect</function>
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and <function>oci_pconnect</function> employ a connection cache; if
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multiple calls to
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<function>oci_connect</function> use the same parameters in a given
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script, the second and subsequent calls return the existing
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connection handle. The cache used
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by <function>oci_connect</function> is cleaned up at the end of the
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script run, or when the connection handle is explicitly closed. The
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function <function>oci_pconnect</function> has similar behavior,
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although its cache is maintained separately and survives between
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HTTP requests.
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</para>
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<para>
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This caching feature means the two handles are not transactionally
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isolated (they are in fact the same connection handle, so there is
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no isolation of any kind). If the application needs two separate,
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transactionally isolated connections, then
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use <function>oci_new_connect</function>.
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</para>
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<para>
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The <function>oci_pconnect</function> cache is cleared and any
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database connections closed when the PHP process terminates, so
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effective use of persistent connections requires that PHP be an
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Apache module or used with FCGI, or similar. Persistent connections
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will not have any benefits over <function>oci_connect</function>
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when PHP is used with CGI or via the command-line.
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</para>
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<para>
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The function <function>oci_new_connect</function> always creates a
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new connection to the Oracle server, regardless of what other
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connections might already exist. High traffic web applications
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should avoid using
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<function>oci_new_connect</function>, especially in the busiest sections of
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the application.
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</para>
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</section>
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<section>
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<title>DRCP Connection Pooling</title>
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<para>
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PHP from 5.3 (PECL OCI8 1.3) supports Oracle Database Resident
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Connection Pooling (DRCP). DRCP allows more efficient use of
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database machine memory and provides high scalability. No, or
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minimal, application changes are needed to use DRCP.
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</para>
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<para>
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DRCP is suited for applications that connect using few database
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schemas and hold database connections open for a short period of
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time. Other applications should use Oracle's
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default <literal>Dedicated</literal> database server processes, or
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use <literal>Shared</literal> servers.
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</para>
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<para>
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DRCP benefits all three connection functions, but gives the highest
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scalability when connections are created
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with <function>oci_pconnect</function>.
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</para>
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<para>
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For DRCP to be available in OCI8, Oracle client libraries used by
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PHP and the version of the Oracle Database must both be 11g or greater.
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</para>
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<para>
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Documentation on DRCP is found in several Oracle manuals. For
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example,
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see <link xlink:href="&url.oracle.drcp.configure;">Configuring
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Database Resident Connection Pooling</link> in the Oracle
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documentation for usage information.
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A <link xlink:href="&url.oracle.drcp.whitepaper;">DRCP
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white paper</link> contains background information on DRCP.
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</para>
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<para>
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To use DRCP, build PHP with the OCI8 1.3 (or later) extension and Oracle 11g (or later)
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libraries and then follow these steps:
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</para>
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<para>
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<itemizedlist>
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<listitem>
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<para>
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As a privileged database administrator, use a program like
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SQL*Plus to start the connection pool in the database:
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</para>
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<para>
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<informalexample>
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<screen>
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<![CDATA[
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SQL> execute dbms_connection_pool.start_pool;
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]]>
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</screen>
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</informalexample>
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</para>
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</listitem>
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<listitem>
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<para>
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Optionally
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use <literal>dbms_connection_pool.alter_param()</literal> to
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configure DRCP settings. The current pool settings can be
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queried from the <literal>DBA_CPOOL_INFO</literal> view.
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</para>
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</listitem>
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<listitem>
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<para>
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Update the connection strings used. For PHP applications that
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currently connect using a Network Connect Name
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like <literal>MYDB</literal>:
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</para>
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<para>
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<informalexample>
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<screen>
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<![CDATA[
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$c = oci_pconnect("myuser", "mypassword", "MYDB");
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]]>
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</screen>
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</informalexample>
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</para>
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<para>
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modify the tnsnames.ora file and add
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a <literal>(SERVER=POOLED)</literal> clause, for example:
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</para>
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<para>
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<informalexample>
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<screen>
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<![CDATA[
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MYDB = (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp) (HOST=myhost.dom.com)
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(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=sales)
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(SERVER=POOLED)))
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]]>
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</screen>
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</informalexample>
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</para>
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<para>
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Alternatively, modify the Easy Connect syntax in PHP and add
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<literal>:POOLED</literal> after the service name:
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</para>
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<para>
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<informalexample>
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<screen>
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<![CDATA[
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$c = oci_pconnect("myuser", "mypassword", "myhost.dom.com:1521/sales:POOLED");
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]]>
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</screen>
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</informalexample>
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</para>
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</listitem>
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<listitem>
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<para>
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Edit &php.ini; and choose a connection class name. This name
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indicates a logical division of the connection pool and can be
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used to isolate pooling for separate applications. Any PHP
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applications with the same user name and connection class value
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will be able to share connections in the pool, giving greater
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scalability.
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</para>
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<para>
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<informalexample>
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<screen>
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<![CDATA[
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oci8.connection_class = "MY_APPLICATION_NAME"
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]]>
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</screen>
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</informalexample>
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</para>
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</listitem>
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<listitem>
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<para>
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Run the application, connecting to the 11g (or later) database.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<note>
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<para>
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Applications using Oracle 10g that require the performance of
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persistent connections can reduce the amount of database server
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memory needed by using Oracle <literal>Shared</literal> servers
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(previously known as Multi Threaded Servers). Refer to Oracle
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documentation for information.
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</para>
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</note>
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</section>
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<section>
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<title>DRCP Recommendations and Known Limitations</title>
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<para>
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Changing a password over DRCP connections will fail with the error
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<emphasis>ORA-56609: Usage not supported with DRCP</emphasis>.
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This is a documented restriction of Oracle Database 11g.
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</para>
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<para>
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From OCI8 1.3, persistent connections can be
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closed by the user, allowing greater control over connection
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resource usage. Persistent connections will now also be closed
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automatically when there is no PHP variable referencing them, such
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as at the end of scope of a PHP user function. This will rollback
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any uncommitted transaction. These changes to persistent
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connections make them behave similarly to non-persistent
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connections, simplifying the interface, allowing for greater
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application consistency and predictability.
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Use <link linkend="ini.oci8.old-oci-close-semantics">oci8.old_oci_close_semantics</link>
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set to
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<emphasis>On</emphasis> to retain the historical behavior.
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</para>
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<para>
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If the Oracle Database is version 11.1.0.6, then the Oracle
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database patch for Oracle bug 6474441 must be applied to use DRCP.
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Without this patch, errors such as <emphasis>ORA-01000: maximum
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open cursors exceeded</emphasis>, <emphasis>ORA-01001 invalid
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cursor</emphasis> or <emphasis>ORA-01002 fetch out of
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sequence</emphasis> may occur. This bug was fixed in Oracle
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11.1.0.7 onwards.
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</para>
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<para>
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If the Oracle 11.1.0.6 database patch cannot be applied, one of the
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following three workarounds can be used instead:
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</para>
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<para>
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<itemizedlist>
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<listitem>
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<simpara>
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Connect using Oracle <literal>Dedicated</literal>
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or <literal>Shared</literal> servers instead of DRCP.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Set PHP's <link linkend="ini.oci8.statement-cache-size">oci8.statement_cache_size</link>
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to 0.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Set an event in the database initialization parameter file:
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<emphasis>event="56699 trace name context forever, level 128"</emphasis>.
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</simpara>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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Oracle Database 11.1.0.7 and the Oracle Database 11.1.0.6 patch for
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Oracle bug 6474441 allow PHP applications with DRCP connection to
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use a database <literal>LOGON</literal> trigger to set session
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properties at the time of session creation. Examples of such
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settings are the NLS language and the date format.
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</para>
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<para>
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If the Oracle 11.1.0.6 database patch cannot be applied, one of the
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following workarounds can be used instead
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of using <literal>LOGON</literal> triggers:
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</para>
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<para>
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<itemizedlist>
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<listitem>
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<simpara>
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After logon, explicitly set the session properties using PHP
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application code.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Connect using Oracle <literal>Dedicated</literal>
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or <literal>Shared</literal> servers instead of DRCP.
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</simpara>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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The automatic re-establishment of PHP persistent connections after
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an Apache or FCGI process respawns means <literal>LOGON</literal>
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triggers in PHP are only recommended for setting session attributes
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and not for per-application user connection requests. This is even
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more so with DRCP due to the automatic pool sizing and with the
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way <literal>LOGON</literal> triggers fire with DRCP
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authentication.
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</para>
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</section>
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</chapter>
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<!-- Keep this comment at the end of the file
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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