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<div id="preamble"><h1>Apache Module mod_dbd</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_dbd.html" title="English">&nbsp;en&nbsp;</a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Manages SQL database connections</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>dbd_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_dbd.c</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Version 2.1 and later</td></tr></table>
<h3>Summary</h3>

    <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> manages SQL database connections using
    <a href="http://people.apache.org/~niq/dbd.html">apr_dbd</a>.
    It provides database connections on request to modules
    requiring SQL database functions, and takes care of
    managing databases with optimal efficiency and scalability
    for both threaded and non-threaded MPMs.</p>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#dbdexptime">DBDExptime</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dbdkeep">DBDKeep</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dbdmax">DBDMax</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dbdmin">DBDMin</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dbdparams">DBDParams</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dbdpersist">DBDPersist</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dbdpreparesql">DBDPrepareSQL</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#dbdriver">DBDriver</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#pooling">Connection Pooling</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#API">Apache DBD API</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#prepared">SQL Prepared Statements</a></li>
</ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="pooling" id="pooling">Connection Pooling</a></h2>
    <p>This module manages database connections, in a manner
    optimised for the platform.  On non-threaded platforms,
    it provides a persistent connection in the manner of
    classic LAMP (Linux, Apache, Mysql, Perl/PHP/Python).
    On threaded platform, it provides an altogether more
    scalable and efficient <em>connection pool</em>, as
    described in <a href="http://www.apachetutor.org/dev/reslist">this article at ApacheTutor</a>. <code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> supersedes
    the modules presented in that article.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="API" id="API">Apache DBD API</a></h2>
    <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> exports five functions for other modules
    to use. The API is as follows:</p>

    <div class="example"><pre><code>typedef struct {
    apr_dbd_t *handle;
    apr_dbd_driver_t *driver;
    apr_hash_t *prepared;
} ap_dbd_t;

/* Export functions to access the database */

/* acquire a connection that MUST be explicitly closed.
 * Returns NULL on error
 */
AP_DECLARE(ap_dbd_t*) ap_dbd_open(apr_pool_t*, server_rec*);

/* release a connection acquired with ap_dbd_open */
AP_DECLARE(void) ap_dbd_close(server_rec*, ap_dbd_t*);

/* acquire a connection that will have the lifetime of a request
 * and MUST NOT be explicitly closed.  Return NULL on error.
 * This is the preferred function for most applications.
 */
AP_DECLARE(ap_dbd_t*) ap_dbd_acquire(request_rec*);

/* acquire a connection that will have the lifetime of a connection
 * and MUST NOT be explicitly closed.  Return NULL on error.
 */
AP_DECLARE(ap_dbd_t*) ap_dbd_cacquire(request_rec*);

/* Prepare a statement for use by a client module */
AP_DECLARE(void) ap_dbd_prepare(server_rec*, const char*, const char*);

/* Also export them as optional functions for modules that prefer it */
APR_DECLARE_OPTIONAL_FN(ap_dbd_t*, ap_dbd_open, (apr_pool_t*, server_rec*));
APR_DECLARE_OPTIONAL_FN(void, ap_dbd_close, (server_rec*, ap_dbd_t*));
APR_DECLARE_OPTIONAL_FN(ap_dbd_t*, ap_dbd_acquire, (request_rec*));
APR_DECLARE_OPTIONAL_FN(ap_dbd_t*, ap_dbd_cacquire, (conn_rec*));
APR_DECLARE_OPTIONAL_FN(void, ap_dbd_prepare, (server_rec*, const char*, const char*));
</code></pre></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="prepared" id="prepared">SQL Prepared Statements</a></h2>
    <p><code class="module"><a href="../mod/mod_dbd.html">mod_dbd</a></code> supports SQL prepared statements on behalf
    of modules that may wish to use them.  Each prepared statement
    must be assigned a name (label), and they are stored in a hash:
    the <code>prepared</code> field of an <code>ap_dbd_t</code>.
    Hash entries are of type <code>apr_dbd_prepared_t</code>
    and can be used in any of the apr_dbd prepared statement
    SQL query or select commands.</p>

    <p>It is up to dbd user modules to use the prepared statements
    and document what statements can be specified in httpd.conf,
    or to provide their own directives and use <code>ap_dbd_prepare</code>.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDExptime" id="DBDExptime">DBDExptime</a> <a name="dbdexptime" id="dbdexptime">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Keepalive time for idle connections</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDExptime <var>time-in-seconds</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>Set the time to keep idle connections alive where the number
    of connections specified in DBDKeep has been exceeded (threaded
    platforms only).</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDKeep" id="DBDKeep">DBDKeep</a> <a name="dbdkeep" id="dbdkeep">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum sustainednumber of connections</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDKeep <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>Set the maximum number of connections per process to be
    sustained, other than for handling peak demand (threaded
    platforms only).</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDMax" id="DBDMax">DBDMax</a> <a name="dbdmax" id="dbdmax">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of connections</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDMax <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>Set the hard maximum number of connections per process
    (threaded platforms only).</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDMin" id="DBDMin">DBDMin</a> <a name="dbdmin" id="dbdmin">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of connections</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDMin <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>Set the minimum number of connections per process (threaded
    platforms only).</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDParams" id="DBDParams">DBDParams</a> <a name="dbdparams" id="dbdparams">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Parameters for database connection</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDParams
<var>param1</var>=<var>value1</var>[,<var>param2</var>=<var>value2</var>]</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>As required by the underlying driver.  Typically this will be
    used to pass whatever cannot be defaulted amongst username,
    password, database name, hostname and port number for connection.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDPersist" id="DBDPersist">DBDPersist</a> <a name="dbdpersist" id="dbdpersist">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Whether to use persistent connections</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDPersist 0|1</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>If set to 0, persistent and pooled connections are disabled.
    A new database connection is opened when requested by a client,
    and closed immediately on release.  This option is for debugging
    and low-usage servers.</p>

    <p>The default is to enable a pool of persistent connections
    (or a single LAMP-style persistent connection in the case of a
    non-threaded server), and should almost always be used in operation.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDPrepareSQL" id="DBDPrepareSQL">DBDPrepareSQL</a> <a name="dbdpreparesql" id="dbdpreparesql">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Define an SQL prepared statement</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDPrepareSQL <var>"SQL statement"</var> <var>label</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>For modules such as authentication that use repeatedly use a
    single SQL statement, optimum performance is achieved by preparing
    the statement at startup rather than every time it is used.
    This directive prepares an SQL statement and assigns it a label.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="DBDriver" id="DBDriver">DBDriver</a> <a name="dbdriver" id="dbdriver">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Specify an SQL driver</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DBDriver <var>name</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_dbd</td></tr>
</table>
    <p>Selects an apr_dbd driver by name.  The driver must be installed
    on your system (on most systems, it will be a shared object or dll).
    For example, <code>DBDriver mysql</code> will select the MySQL
    driver in apr_dbd_mysql.so.</p>

</div>
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