package Apache::DBI;

use DBI ();
use strict;

#$Id: DBI.pm,v 1.12 1997/06/30 20:12:22 mergl Exp $

require_version DBI 0.85;

$Apache::DBI::VERSION = '0.71';

$Apache::DBI::DEBUG = 0;


my %Connected;

sub connect {

    my $class = shift;
    unshift @_, $class if ref $class;
    my $drh  = shift;
    my @args = map { defined $_ ? $_ : "" } @_;
    my $idx  = join (":", (@args));

    if (($Connected{$idx} && $Connected{$idx}->ping)) {
        print STDERR "Pid = $$, Apache::DBI::connect already connected to '$idx'\n" if $Apache::DBI::DEBUG;
        return (bless $Connected{$idx}, 'Apache::DBI::db') if ($Connected{$idx} && $Connected{$idx}->ping);
    }

    $Connected{$idx} = $drh->connect(@args);
    $Connected{$idx}->{InactiveDestroy} = 1;
    print STDERR "Pid = $$, Apache::DBI::connect new connect to '$idx'\n" if $Apache::DBI::DEBUG;
    return (bless $Connected{$idx}, 'Apache::DBI::db');
}


{ package Apache::DBI::db;
  no strict;
  @ISA=qw(DBI::db);
  use strict;
  sub disconnect {1};
}


Apache::Status->menu_item(

    'DBI' => 'DBI connections',
    sub {
        my($r, $q) = @_;
        my(@s) = qw(<TABLE><TR><TD>Database</TD><TD>Username</TD></TR>);
        for (keys %Connected) {
            push @s, '<TR><TD>', join('</TD><TD>', (split(':', $_))[0,1]), "</TD></TR>\n";
        }
        push @s, '</TABLE>';
        return \@s;
   }

) if ($INC{'Apache.pm'} && Apache->module('Apache::Status'));


1;

__END__


=head1 NAME

Apache::DBI - Initiate a persistent database connection


=head1 SYNOPSIS

 # Configuration in httpd.conf or srm.conf

 PerlModule Apache::DBI


=head1 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 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 hides the 
database handle. 

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. 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 new 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. 

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. 


=head1 SEE ALSO

Apache(3), DBI(3)


=head1 AUTHORS

 mod_perl by Doug MacEachern <dougm@osf.org>
 DBI by Tim Bunce <Tim.Bunce@ig.co.uk>
 Apache::DBI by Edmund Mergl <E.Mergl@bawue.de>