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

<name>mod_dbd</name>

<description>Manages SQL database connections</description>

<status>Experimental</status>

<sourcefile>mod_dbd.c</sourcefile>

<identifier>dbd_module</identifier>

<compatibility>Version 2.1 and higher</compatibility>

<summary>

<p>mod_dbd 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="reslist"><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"

title="Connection pooling in Apache">this article at ApacheTutor</a>.

mod_dbd supersedes the modules presented in that article.</p>

</section>

<section id="API"><title>Apache DBD API</title>

<p>mod_dbd exports three functions for other modules to use.

The API is as follows:</p>

<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*);

/* 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*));

</code></pre>

</section>

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

<p>mod_dbd 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.</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, <samp>DBDriver mysql</samp> 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=value1,param2=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 <var>[0|1]</var></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>