Apache HTTP Server Version 2.2
Apache HTTP Server Version 2.2
| Description: | Manages SQL database connections |
|---|---|
| Status: | Extension |
| Module Identifier: | dbd_module |
| Source File: | mod_dbd.c |
| Compatibility: | Version 2.1 and later |
mod_dbd manages SQL database connections using
apr_dbd.
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.
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. mod_dbd supersedes
the modules presented in that article.
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*));
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.
| Description: | Keepalive time for idle connections |
|---|---|
| Syntax: | DBDExptime time-in-seconds |
| 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).
| Description: | Maximum sustainednumber of connections |
|---|---|
| Syntax: | DBDKeep number |
| 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).
| Description: | Maximum number of connections |
|---|---|
| Syntax: | DBDMax number |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
Set the hard maximum number of connections per process (threaded platforms only).
| Description: | Minimum number of connections |
|---|---|
| Syntax: | DBDMin number |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
Set the minimum number of connections per process (threaded platforms only).
| 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:
PQconnectdbpart1:part2 is used as sqlite_open(part1, atoi(part2), NULL)sqlite3_open| Description: | Whether to use persistent connections |
|---|---|
| Syntax: | DBDPersist 0|1 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_dbd |
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.
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.
| 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.
| 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.