apache/docs/manual/mod/mod_dbd.xml

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<modulesynopsis metafile="mod_dbd.xml.meta">

<name>mod_dbd</name>
<description>Manages SQL database connections</description>
<status>Extension</status>
<sourcefile>mod_dbd.c</sourcefile>
<identifier>dbd_module</identifier>
<compatibility>Version 2.1 and later</compatibility>

<summary>
    <p><module>mod_dbd</module> 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>
</summary>

<section id="pooling"><title>Connection Pooling</title>
    <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>. <module>mod_dbd</module> supersedes
    the modules presented in that article.</p>
</section>

<section id="API"><title>Apache DBD API</title>
    <p><module>mod_dbd</module> exports five functions for other modules
    to use. The API is as follows:</p>

    <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>
    </example>
</section>

<section id="prepared"><title>SQL Prepared Statements</title>
    <p><module>mod_dbd</module> 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>
</section>

<directivesynopsis>
<name>DBDriver</name>
<description>Specify an SQL driver</description>
<syntax>DBDriver <var>name</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <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>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DBDParams</name>
<description>Parameters for database connection</description>
<syntax>DBDParams
<var>param1</var>=<var>value1</var>[,<var>param2</var>=<var>value2</var>]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <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>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DBDPersist</name>
<description>Whether to use persistent connections</description>
<syntax>DBDPersist 0|1</syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <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>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DBDPrepareSQL</name>
<description>Define an SQL prepared statement</description>
<syntax>DBDPrepareSQL <var>"SQL statement"</var> <var>label</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <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>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DBDMin</name>
<description>Minimum number of connections</description>
<syntax>DBDMin <var>number</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>Set the minimum number of connections per process (threaded
    platforms only).</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DBDKeep</name>
<description>Maximum sustainednumber of connections</description>
<syntax>DBDKeep <var>number</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>Set the maximum number of connections per process to be
    sustained, other than for handling peak demand (threaded
    platforms only).</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DBDMax</name>
<description>Maximum number of connections</description>
<syntax>DBDMax <var>number</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>Set the hard maximum number of connections per process
    (threaded platforms only).</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>DBDExptime</name>
<description>Keepalive time for idle connections</description>
<syntax>DBDExptime <var>time-in-seconds</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>Set the time to keep idle connections alive where the number
    of connections specified in DBDKeep has been exceeded (threaded
    platforms only).</p>
</usage>
</directivesynopsis>

</modulesynopsis>