Manuel Apache
Apache Module mod_dbd
| Description: | Manages SQL database connections |
|---|---|
| Status: | Extension |
| Module Identifier: | dbd_module |
| Source File: | mod_dbd.c |
| Compatibility: | Version 2.1 and later |
Summary
mod_dbd manages SQL database connections using APR. 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. For details, see the APR website and this overview of the Apache DBD Framework by its original developer.
Directives
Topics
See also
Connection Pooling
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 connection pool, as described in this article at ApacheTutor. Note that mod_dbd supersedes the modules presented in that article.
Apache DBD API
mod_dbd exports five functions for other modules to use. The API is as follows:
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*));
SQL Prepared Statements
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 prepared field of an ap_dbd_t. Hash entries are of type apr_dbd_prepared_t and can be used in any of the apr_dbd prepared statement SQL query or select commands.
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 ap_dbd_prepare.
DBDExptime Directive
| Description: | Keepalive time for idle connections |
|---|---|
| Syntax: | DBDExptime time-in-seconds |
| Default: | DBDExptime 300 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
Set the time to keep idle connections alive where the number of connections specified in DBDKeep has been exceeded (threaded platforms only).
DBDKeep Directive
| Description: | Maximum sustained number of connections |
|---|---|
| Syntax: | DBDKeep number |
| Default: | DBDKeep 2 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
Set the maximum number of connections per process to be sustained, other than for handling peak demand (threaded platforms only).
DBDMax Directive
| Description: | Maximum number of connections |
|---|---|
| Syntax: | DBDMax number |
| Default: | DBDMax 10 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
Set the hard maximum number of connections per process (threaded platforms only).
DBDMin Directive
| Description: | Minimum number of connections |
|---|---|
| Syntax: | DBDMin number |
| Default: | DBDMin 1 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
Set the minimum number of connections per process (threaded platforms only).
DBDParams Directive
| Description: | Parameters for database connection |
|---|---|
| Syntax: | DBDParams param1=value1[,param2=value2] |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
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.
Connection string parameters for current drivers include:
- MySQL
- host, port, user, pass, dbname, sock
- Oracle
- user, pass, dbname, server
- PostgreSQL
- The connection string is passed straight through to
PQconnectdb - SQLite2
- The connection string is split on a colon, and
part1:part2is used assqlite_open(part1, atoi(part2), NULL) - SQLite3
- The connection string is passed straight through to
sqlite3_open
DBDPersist Directive
| Description: | Whether to use persistent connections |
|---|---|
| Syntax: | DBDPersist On|Off |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
If set to Off, 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.
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.
Prior to version 2.2.2, this directive accepted only the values 0 and 1 instead of Off and On, respectively.
DBDPrepareSQL Directive
| Description: | Define an SQL prepared statement |
|---|---|
| Syntax: | DBDPrepareSQL "SQL statement" label |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
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.
DBDriver Directive
| Description: | Specify an SQL driver |
|---|---|
| Syntax: | DBDriver name |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
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, DBDriver mysql will select the MySQL driver in apr_dbd_mysql.so.
Remonter 
