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23 <modulesynopsis metafile="mod_dbd.xml.meta">
26 <description>Manages SQL database connections</description>
27 <status>Extension</status>
28 <sourcefile>mod_dbd.c</sourcefile>
29 <identifier>dbd_module</identifier>
30 <compatibility>Version 2.1 and later</compatibility>
33 <p><module>mod_dbd</module> manages SQL database connections using
34 <glossary>APR</glossary>. It provides database connections on request
35 to modules requiring SQL database functions, and takes care of
36 managing databases with optimal efficiency and scalability
37 for both threaded and non-threaded MPMs. For details, see the
38 <a href="http://apr.apache.org/">APR</a> website and this overview of the
39 <a href="http://people.apache.org/~niq/dbd.html">Apache DBD Framework</a>
40 by its original developer.
44 <seealso><a href="../misc/password_encryptions.html">Password Formats</a></seealso>
46 <section id="pooling"><title>Connection Pooling</title>
47 <p>This module manages database connections, in a manner
48 optimised for the platform. On non-threaded platforms,
49 it provides a persistent connection in the manner of
50 classic LAMP (Linux, Apache, Mysql, Perl/PHP/Python).
51 On threaded platform, it provides an altogether more
52 scalable and efficient <em>connection pool</em>, as
53 described in <a href="http://www.apachetutor.org/dev/reslist">this
54 article at ApacheTutor</a>. Note that <module>mod_dbd</module>
55 supersedes the modules presented in that article.</p>
58 <section id="API"><title>Apache DBD API</title>
59 <p><module>mod_dbd</module> exports five functions for other modules
60 to use. The API is as follows:</p>
63 <pre><code>typedef struct {
65 apr_dbd_driver_t *driver;
69 /* Export functions to access the database */
71 /* acquire a connection that MUST be explicitly closed.
72 * Returns NULL on error
74 AP_DECLARE(ap_dbd_t*) ap_dbd_open(apr_pool_t*, server_rec*);
76 /* release a connection acquired with ap_dbd_open */
77 AP_DECLARE(void) ap_dbd_close(server_rec*, ap_dbd_t*);
79 /* acquire a connection that will have the lifetime of a request
80 * and MUST NOT be explicitly closed. Return NULL on error.
81 * This is the preferred function for most applications.
83 AP_DECLARE(ap_dbd_t*) ap_dbd_acquire(request_rec*);
85 /* acquire a connection that will have the lifetime of a connection
86 * and MUST NOT be explicitly closed. Return NULL on error.
88 AP_DECLARE(ap_dbd_t*) ap_dbd_cacquire(request_rec*);
90 /* Prepare a statement for use by a client module */
91 AP_DECLARE(void) ap_dbd_prepare(server_rec*, const char*, const char*);
93 /* Also export them as optional functions for modules that prefer it */
94 APR_DECLARE_OPTIONAL_FN(ap_dbd_t*, ap_dbd_open, (apr_pool_t*, server_rec*));
95 APR_DECLARE_OPTIONAL_FN(void, ap_dbd_close, (server_rec*, ap_dbd_t*));
96 APR_DECLARE_OPTIONAL_FN(ap_dbd_t*, ap_dbd_acquire, (request_rec*));
97 APR_DECLARE_OPTIONAL_FN(ap_dbd_t*, ap_dbd_cacquire, (conn_rec*));
98 APR_DECLARE_OPTIONAL_FN(void, ap_dbd_prepare, (server_rec*, const char*, const char*));
103 <section id="prepared"><title>SQL Prepared Statements</title>
104 <p><module>mod_dbd</module> supports SQL prepared statements on behalf
105 of modules that may wish to use them. Each prepared statement
106 must be assigned a name (label), and they are stored in a hash:
107 the <code>prepared</code> field of an <code>ap_dbd_t</code>.
108 Hash entries are of type <code>apr_dbd_prepared_t</code>
109 and can be used in any of the apr_dbd prepared statement
110 SQL query or select commands.</p>
112 <p>It is up to dbd user modules to use the prepared statements
113 and document what statements can be specified in httpd.conf,
114 or to provide their own directives and use <code>ap_dbd_prepare</code>.</p>
117 <section id="security">
118 <title>SECURITY WARNING</title>
119 <p>Any web/database application needs to secure itself against SQL
120 injection attacks. In most cases, Apache DBD is safe, because
121 applications use prepared statements, and untrusted inputs are
122 only ever used as data. Of course, if you use it via third-party
123 modules, you should ascertain what precautions they may require.</p>
124 <p>However, the <var>FreeTDS</var> driver is inherently
125 <strong>unsafe</strong>. The underlying library doesn't support
126 prepared statements, so the driver emulates them, and the
127 untrusted input is merged into the SQL statement.</p>
128 <p>It can be made safe by <em>untainting</em> all inputs:
129 a process inspired by Perl's taint checking. Each input
130 is matched against a regexp, and only the match is used,
131 according to the Perl idiom:</p>
133 <pre><code> $untrusted =~ /([a-z]+)/;
134 $trusted = $1;</code></pre>
136 <p>To use this, the untainting regexps must be included in the
137 prepared statements configured. The regexp follows immediately
138 after the % in the prepared statement, and is enclosed in
139 curly brackets {}. For example, if your application expects
140 alphanumeric input, you can use:</p>
142 <code>"SELECT foo FROM bar WHERE input = %s"</code>
144 <p>with other drivers, and suffer nothing worse than a failed query.
145 But with FreeTDS you'd need:</p>
147 <code>"SELECT foo FROM bar WHERE input = %{([A-Za-z0-9]+)}s"</code>
149 <p>Now anything that doesn't match the regexp's $1 match is
150 discarded, so the statement is safe.</p>
151 <p>An alternative to this may be the third-party ODBC driver,
152 which offers the security of genuine prepared statements.</p>
155 <name>DBDriver</name>
156 <description>Specify an SQL driver</description>
157 <syntax>DBDriver <var>name</var></syntax>
158 <contextlist><context>server config</context><context>virtual host</context>
162 <p>Selects an apr_dbd driver by name. The driver must be installed
163 on your system (on most systems, it will be a shared object or dll).
164 For example, <code>DBDriver mysql</code> will select the MySQL
165 driver in apr_dbd_mysql.so.</p>
170 <name>DBDParams</name>
171 <description>Parameters for database connection</description>
173 <var>param1</var>=<var>value1</var>[,<var>param2</var>=<var>value2</var>]</syntax>
174 <contextlist><context>server config</context><context>virtual host</context>
178 <p>As required by the underlying driver. Typically this will be
179 used to pass whatever cannot be defaulted amongst username,
180 password, database name, hostname and port number for connection.</p>
181 <p>Connection string parameters for current drivers include:</p>
183 <dt>FreeTDS (for MSSQL and SyBase)</dt>
184 <dd>username, password, appname, dbname, host, charset, lang, server</dd>
186 <dd>host, port, user, pass, dbname, sock, flags, fldsz, group, reconnect</dd>
188 <dd>user, pass, dbname, server</dd>
190 <dd>The connection string is passed straight through to <code>PQconnectdb</code></dd>
192 <dd>The connection string is split on a colon, and <code>part1:part2</code> is used as <code>sqlite_open(part1, atoi(part2), NULL)</code></dd>
194 <dd>The connection string is passed straight through to <code>sqlite3_open</code></dd>
196 <dd>datasource, user, password, connect, ctimeout, stimeout, access, txmode, bufsize</dd>
202 <name>DBDPersist</name>
203 <description>Whether to use persistent connections</description>
204 <syntax>DBDPersist On|Off</syntax>
205 <contextlist><context>server config</context><context>virtual host</context>
209 <p>If set to Off, persistent and pooled connections are disabled.
210 A new database connection is opened when requested by a client,
211 and closed immediately on release. This option is for debugging
212 and low-usage servers.</p>
214 <p>The default is to enable a pool of persistent connections
215 (or a single LAMP-style persistent connection in the case of a
216 non-threaded server), and should almost always be used in operation.</p>
218 <p>Prior to version 2.2.2, this directive accepted only the values
219 <code>0</code> and <code>1</code> instead of <code>Off</code> and
220 <code>On</code>, respectively.</p>
225 <name>DBDPrepareSQL</name>
226 <description>Define an SQL prepared statement</description>
227 <syntax>DBDPrepareSQL <var>"SQL statement"</var> <var>label</var></syntax>
228 <contextlist><context>server config</context><context>virtual host</context>
232 <p>For modules such as authentication that repeatedly use a
233 single SQL statement, optimum performance is achieved by preparing
234 the statement at startup rather than every time it is used.
235 This directive prepares an SQL statement and assigns it a label.</p>
241 <description>Minimum number of connections</description>
242 <syntax>DBDMin <var>number</var></syntax>
243 <default>DBDMin 1</default>
244 <contextlist><context>server config</context><context>virtual host</context>
248 <p>Set the minimum number of connections per process (threaded
255 <description>Maximum sustained number of connections</description>
256 <syntax>DBDKeep <var>number</var></syntax>
257 <default>DBDKeep 2</default>
258 <contextlist><context>server config</context><context>virtual host</context>
262 <p>Set the maximum number of connections per process to be
263 sustained, other than for handling peak demand (threaded
270 <description>Maximum number of connections</description>
271 <syntax>DBDMax <var>number</var></syntax>
272 <default>DBDMax 10</default>
273 <contextlist><context>server config</context><context>virtual host</context>
277 <p>Set the hard maximum number of connections per process
278 (threaded platforms only).</p>
283 <name>DBDExptime</name>
284 <description>Keepalive time for idle connections</description>
285 <syntax>DBDExptime <var>time-in-seconds</var></syntax>
286 <default>DBDExptime 300</default>
287 <contextlist><context>server config</context><context>virtual host</context>
291 <p>Set the time to keep idle connections alive when the number
292 of connections specified in DBDKeep has been exceeded (threaded