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<h1>OCI8 Connection Handling and Connection Pooling</h1>
<div class="section">
<h2 class="title">Connection Functions</h2>
<p class="para">
The OCI8 extension provides three different functions for
connecting to Oracle. The standard connection function
is <span class="function"><a href="function.oci-connect.html" class="function">oci_connect()</a></span>. This creates a connection to
an Oracle database and returns a resource used by subsequent
database calls.
</p>
<p class="para">
Connecting to an Oracle server is a reasonably expensive operation
in terms of the time that it takes to complete.
The <span class="function"><a href="function.oci-pconnect.html" class="function">oci_pconnect()</a></span> 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).
</p>
<p class="para">
If the application connects to Oracle using a different set of
credentials for each web user, the persistent cache employed by
<span class="function"><a href="function.oci-pconnect.html" class="function">oci_pconnect()</a></span> 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 <a href="oci8.configuration.html#ini.oci8.max-persistent" class="link">oci8.max_persistent</a>
and <a href="oci8.configuration.html#ini.oci8.persistent-timeout" class="link">oci8.persistent_timeout</a>
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
<span class="function"><a href="function.oci-connect.html" class="function">oci_connect()</a></span> instead.
</p>
<p class="para">
Both <span class="function"><a href="function.oci-connect.html" class="function">oci_connect()</a></span>
and <span class="function"><a href="function.oci-pconnect.html" class="function">oci_pconnect()</a></span> employ a connection cache; if
multiple calls to
<span class="function"><a href="function.oci-connect.html" class="function">oci_connect()</a></span> use the same parameters in a given
script, the second and subsequent calls return the existing
connection handle. The cache used
by <span class="function"><a href="function.oci-connect.html" class="function">oci_connect()</a></span> is cleaned up at the end of the
script run, or when the connection handle is explicitly closed. The
function <span class="function"><a href="function.oci-pconnect.html" class="function">oci_pconnect()</a></span> has similar behavior,
although its cache is maintained separately and survives between
HTTP requests.
</p>
<p class="para">
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 <span class="function"><a href="function.oci-new-connect.html" class="function">oci_new_connect()</a></span>.
</p>
<p class="para">
The <span class="function"><a href="function.oci-pconnect.html" class="function">oci_pconnect()</a></span> 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 FGCI, or similar. Persistent connections
will not have any benefits over <span class="function"><a href="function.oci-connect.html" class="function">oci_connect()</a></span>
when PHP is used with CGI or via the command-line.
</p>
<p class="para">
The function <span class="function"><a href="function.oci-new-connect.html" class="function">oci_new_connect()</a></span> always creates a
new connection to the Oracle server, regardless of what other
connections might already exist. High traffic web applications
should avoid using
<span class="function"><a href="function.oci-new-connect.html" class="function">oci_new_connect()</a></span>, especially in the busiest sections of
the application.
</p>
</div>
<div class="section">
<h2 class="title">DRCP Connection Pooling</h2>
<p class="para">
PHP from 5.3 (PECL OCI8 1.3) 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.
</p>
<p class="para">
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 <em>Dedicated</em> database server processes, or
use <em>Shared</em> servers.
</p>
<p class="para">
DRCP benefits all three connection functions, but gives the highest
scalability when connections are created
with <span class="function"><a href="function.oci-pconnect.html" class="function">oci_pconnect()</a></span>.
</p>
<p class="para">
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.
</p>
<p class="para">
Documentation on DRCP is found in several Oracle manuals. For
example,
see <a href="http://download.oracle.com/docs/cd/E11882_01/server.112/e25494/manproc004.htm" class="link external">» Configuring
Database Resident Connection Pooling</a> in the Oracle
documentation for usage information.
A <a href="http://www.oracle.com/technetwork/topics/php/whatsnew/php-scalability-ha-twp-128842.pdf" class="link external">» DRCP
white paper</a> contains background information on DRCP.
</p>
<p class="para">
To use DRCP, build PHP with the OCI8 1.3 (or later) extension and Oracle 11g (or later)
libraries and then follow these steps:
</p>
<p class="para">
<ul class="itemizedlist">
<li class="listitem">
<p class="para">
As a privileged database administrator, use a program like
SQL*Plus to start the connection pool in the database:
</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
SQL> execute dbms_connection_pool.start_pool;
</pre></div>
</div>
</div>
</p>
</li>
<li class="listitem">
<p class="para">
Optionally
use <em>dbms_connection_pool.alter_param()</em> to
configure DRCP settings. The current pool settings can be
queried from the <em>DBA_CPOOL_INFO</em> view.
</p>
</li>
<li class="listitem">
<p class="para">
Update the connection strings used. For PHP applications that
currently connect using a Network Connect Name
like <em>MYDB</em>:
</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
$c = oci_pconnect("myuser", "mypassword", "MYDB");
</pre></div>
</div>
</div>
</p>
<p class="para">
modify the tnsnames.ora file and add
a <em>(SERVER=POOLED)</em> clause, for example:
</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
MYDB = (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp) (HOST=myhost.dom.com)
(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=sales)
(SERVER=POOLED)))
</pre></div>
</div>
</div>
</p>
<p class="para">
Alternatively, modify the Easy Connect syntax in PHP and add
<em>:POOLED</em> after the service name:
</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
$c = oci_pconnect("myuser", "mypassword", "myhost.dom.com:1521/sales:POOLED");
</pre></div>
</div>
</div>
</p>
</li>
<li class="listitem">
<p class="para">
Edit <var class="filename">php.ini</var> and choose a connection class name. This name
indicates a logical division of the connection pool and can be
used to isolate pooling for separate applications. Any PHP
applications with the same user name and connection class value
will be able to share connections in the pool, giving greater
scalability.
</p>
<p class="para">
<div class="informalexample">
<div class="example-contents screen">
<div class="cdata"><pre>
oci8.connection_class = "MY_APPLICATION_NAME"
</pre></div>
</div>
</div>
</p>
</li>
<li class="listitem">
<p class="para">
Run the application, connecting to the 11g (or later) database.
</p>
</li>
</ul>
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Applications using Oracle 10g that require the performance of
persistent connections can reduce the amount of database server
memory needed by using Oracle <em>Shared</em> servers
(previously known as Multi Threaded Servers). Refer to Oracle
documentation for information.
</p>
</p></blockquote>
</div>
<div class="section">
<h2 class="title">DRCP Recommendations and Known Limitations</h2>
<p class="para">
Changing a password over DRCP connections will fail with the error
<em class="emphasis">ORA-56609: Usage not supported with DRCP</em>.
This is a documented restriction of Oracle Database 11g.
</p>
<p class="para">
From OCI8 1.3, 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 <a href="oci8.configuration.html#ini.oci8.old-oci-close-semantics" class="link">oci8.old_oci_close_semantics</a>
set to
<em class="emphasis">On</em> to retain the historical behavior.
</p>
<p class="para">
If the Oracle Database is version 11.1.0.6, then the Oracle
database patch for Oracle bug 6474441 must be applied to use DRCP.
Without this patch, errors such as <em class="emphasis">ORA-01000: maximum
open cursors exceeded</em>, <em class="emphasis">ORA-01001 invalid
cursor</em> or <em class="emphasis">ORA-01002 fetch out of
sequence</em> may occur. This bug was fixed in Oracle
11.1.0.7 onwards.
</p>
<p class="para">
If the Oracle 11.1.0.6 database patch cannot be applied, one of the
following three workarounds can be used instead:
</p>
<p class="para">
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
Connect using Oracle <em>Dedicated</em>
or <em>Shared</em> servers instead of DRCP.
</span>
</li>
<li class="listitem">
<span class="simpara">
Set PHP's <a href="oci8.configuration.html#ini.oci8.statement-cache-size" class="link">oci8.statement_cache_size</a>
to 0.
</span>
</li>
<li class="listitem">
<span class="simpara">
Set an event in the database initialization parameter file:
<em class="emphasis">event="56699 trace name context forever, level 128"</em>.
</span>
</li>
</ul>
</p>
<p class="para">
Oracle Database 11.1.0.7 and the Oracle Database 11.1.0.6 patch for
Oracle bug 6474441 allow PHP applications with DRCP connection to
use a database <em>LOGON</em> trigger to set session
properties at the time of session creation. Examples of such
settings are the NLS language and the date format.
</p>
<p class="para">
If the Oracle 11.1.0.6 database patch cannot be applied, one of the
following workarounds can be used instead
of using <em>LOGON</em> triggers:
</p>
<p class="para">
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
After logon, explicitly set the session properties using PHP
application code.
</span>
</li>
<li class="listitem">
<span class="simpara">
Connect using Oracle <em>Dedicated</em>
or <em>Shared</em> servers instead of DRCP.
</span>
</li>
</ul>
</p>
<p class="para">
The automatic re-establishment of PHP persistent connections after
an Apache or FGCI process respawns means <em>LOGON</em>
triggers in PHP are only recommended for setting session attributes
and not for per-application user connection requests. This is even
more so with DRCP due to the automatic pool sizing and with the
way <em>LOGON</em> triggers fire with DRCP
authentication.
</p>
</div>
</div>
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