NAME

Apache::DBI - Initiate a persistent database connection

SYNOPSIS

 # Configuration in httpd.conf or srm.conf:

 PerlModule Apache::DBI  # this comes before all other ApacheDBI modules

DESCRIPTION

This module initiates a persistent database connection.

The database access uses Perl's DBI. For supported DBI drivers see:

 http://www.hermetica.com/technologia/DBI/

When loading the DBI module (do not confuse this with the Apache::DBI module) it looks if the environment variable GATEWAY_INTERFACE starts with 'CGI-Perl' and if the module Apache::DBI has been loaded. In this case every connect request will be forwarded to the Apache::DBI module. This looks if a database handle from a previous connect request is already stored and if this handle is still valid using the ping method. If these two conditions are fulfilled it just returns the database handle. If there is no appropriate database handle or if the ping method fails, a new connection is established and the handle is stored for later re-use. There is no need to delete the disconnect statements from your code. They won't do anything because the Apache::DBI module overloads the disconnect method with a NOP.

The Apache::DBI module still has a limitation: it keeps database connections persistent on a per process basis. The problem is, if a user accesses several times a database, the http requests will be handled very likely by different httpd children. Every child process needs to do its own connect. It would be nice, if all httpd children could share the database handles. Currently this is not possible, because of the distinct name-space of every process. Also it is not possible to initiate one database handle upon startup of the httpd and then inheriting this handle to every subsequent child. Whenever one of the children dies, this common handle becomes invalid. One possible solution might be a threaded Apache version.

With this limitation in mind, there are scenarios, where the usage of Apache::DBI.pm is depreciated. Think about a heavy loaded Web-site where every user connects to the database with a unique userid. Every httpd child would create many database handles each of which spawning a new backend process. In a short time this would kill the web server.

Another problem are timeouts: some databases disconnect the client after a certain time of inactivity. The module tries to validate the database handle using the ping-method of the DBI-module. This method returns true as default. If the database handle is not valid and the driver module has no implementation for the ping method, you will get an error when accessing the database. As a work-around you can try to replace the ping method by any database command, which is cheap and safe.

Here is generalized ping method, which can be added to the driver module:

{ package DBD::xxx::db; # ====== DATABASE ====== use strict;

    sub ping {
        my($dbh) = @_;
        local $dbh->{RaiseError} = 0 if $dbh->{RaiseError};
        # adapt the select statement to you database:
        my $sth = $dbh->prepare( "SELECT 1") or return 0;
        $sth->execute or return 0;
        # depending upon the database a prepare is sufficient:
        my $ret = $sth->fetchrow_array;
        $sth->finish;
        return $ret;
    }
}

This module plugs in a menu item for Apache::Status. The menu lists the current database connections. It should be considered incomplete because of the limitations explained above. It shows the current database connections for one specific httpd process, the one which happens to serve the current request. Other httpd children might have other database connections. The Apache::Status module has to be loaded before the Apache::DBI module !

CONFIGURATION

The module should be loaded upon startup of the Apache daemon. Add the following line to your httpd.conf or srm.conf:

 PerlModule Apache::DBI

It is important, to load this module before any other ApacheDBI module !

The module provides the additional method:

 Apache::DBI->connect_on_init($data_source, $username, $auth, \%attr)

This can be used as a simple way to have apache children establish connections on server startup. This call should be in a startup file (PerlModule, <Perl> or PerlRequire). It will establish a connection when a child is started in that child process. Note that this needs mod_perl-1.08 or higher, apache_1.3.0 or higher and that mod_perl needs to be configured with

  PERL_CHILD_INIT=1 PERL_STACKED_HANDLERS=1

For the menu item 'DBI connections' you need to call Apache::Status BEFORE Apache::DBI ! For an example of the configuration order see startup.pl.

PREREQUISITES

For Apache::DBI you need to enable the appropriate call-back hooks when making mod_perl:

  perl Makefile.PL PERL_CHILD_INIT=1 PERL_STACKED_HANDLERS=1. 

SEE ALSO

Apache, mod_perl, DBI

AUTHORS

• mod_perl by Doug MacEachern <dougm@osf.org>

• DBI by Tim Bunce <Tim.Bunce@ig.co.uk>

• Apache::AuthenDBI by Edmund Mergl <E.Mergl@bawue.de>

COPYRIGHT

The Apache::DBI module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

cpanm mod_perl

perl -MCPAN -e shell
install mod_perl