package Apache::DBI;
use strict;
BEGIN { eval { require Apache } }
use DBI ();
use Carp qw(carp);
require_version DBI 1.00;
$Apache::DBI::VERSION = '0.94';
$Apache::DBI::DEBUG = 0;
my %Connected; my @ChildConnect; my %Rollback; my %PingTimeOut; my %LastPingTime; my $Idx;
sub connect_on_init {
carp "Apache.pm was not loaded\n" and return unless $INC{'Apache.pm'};
if(!@ChildConnect and Apache->can('push_handlers')) {
Apache->push_handlers(PerlChildInitHandler => \&childinit);
}
push @ChildConnect, [@_];
}
sub setPingTimeOut {
my $class = shift;
my $data_source = shift;
my $timeout = shift;
if ($data_source =~ /dbi:\w+:.*/ and $timeout =~ /\-*\d+/) {
$PingTimeOut{$data_source} = $timeout;
}
}
sub connect {
my $class = shift;
unshift @_, $class if ref $class;
my $drh = shift;
my @args = map { defined $_ ? $_ : "" } @_;
my $dsn = "dbi:$drh->{Name}:$args[0]";
my $prefix = "$$ Apache::DBI ";
$Idx = join $;, $args[0], $args[1], $args[2];
if (3 == $ map { $Idx .= "$;$_=" .
(defined $args[3]->{$_}
? $args[3]->{$_}
: '')
} sort keys %{$args[3]};
} elsif (3 == $ pop @args;
}
if ($Apache::ServerStarting and $Apache::ServerStarting == 1) {
print STDERR "$prefix skipping connection during server startup, read the docu !!\n" if $Apache::DBI::DEBUG > 1;
return $drh->connect(@args);
}
my $needCleanup = ($Idx =~ /AutoCommit[^\d]+0/) ? 1 : 0;
if(!$Rollback{$Idx} and $needCleanup and Apache->can('push_handlers')) {
print STDERR "$prefix push PerlCleanupHandler \n" if $Apache::DBI::DEBUG > 1;
Apache->push_handlers("PerlCleanupHandler", \&cleanup);
$Rollback{$Idx} = 1;
}
$PingTimeOut{$dsn} = 0 unless $PingTimeOut{$dsn};
$LastPingTime{$dsn} = 0 unless $LastPingTime{$dsn};
my $now = time;
my $needping = (($PingTimeOut{$dsn} == 0 or $PingTimeOut{$dsn} > 0)
and (($now - $LastPingTime{$dsn}) >= $PingTimeOut{$dsn})
) ? 1 : 0;
print STDERR "$prefix need ping: ", $needping == 1 ? "yes" : "no", "\n" if $Apache::DBI::DEBUG > 1;
$LastPingTime{$dsn} = $now;
if ($Connected{$Idx} and (!$needping or eval{$Connected{$Idx}->ping})) {
print STDERR "$prefix already connected to '$Idx'\n" if $Apache::DBI::DEBUG > 1;
return (bless $Connected{$Idx}, 'Apache::DBI::db');
}
delete $Connected{$Idx};
$Connected{$Idx} = $drh->connect(@args);
return undef if !$Connected{$Idx};
print STDERR "$prefix new connect to '$Idx'\n" if $Apache::DBI::DEBUG;
return (bless $Connected{$Idx}, 'Apache::DBI::db');
}
sub childinit {
my $prefix = "$$ Apache::DBI ";
print STDERR "$prefix PerlChildInitHandler \n" if $Apache::DBI::DEBUG > 1;
if (@ChildConnect) {
for my $aref (@ChildConnect) {
shift @$aref;
DBI->connect(@$aref);
$LastPingTime{@$aref[0]} = time;
}
}
1;
}
sub cleanup {
my $prefix = "$$ Apache::DBI ";
print STDERR "$prefix PerlCleanupHandler \n" if $Apache::DBI::DEBUG > 1;
my $dbh = $Connected{$Idx};
if ($Rollback{$Idx} and $dbh and $dbh->{Active} and !$dbh->{AutoCommit} and eval {$dbh->rollback}) {
print STDERR "$prefix PerlCleanupHandler rollback for $Idx \n" if $Apache::DBI::DEBUG > 1;
}
delete $Rollback{$Idx};
1;
}
sub all_handlers {
return \%Connected;
}
@Apache::DBI::st::ISA = ('DBI::st');
{ package Apache::DBI::db;
no strict;
@ISA=qw(DBI::db);
use strict;
sub disconnect {
my $prefix = "$$ Apache::DBI ";
print STDERR "$prefix disconnect (overloaded) \n" if $Apache::DBI::DEBUG > 1;
1;
};
}
Apache::Status->menu_item(
'DBI' => 'DBI connections',
sub {
my($r, $q) = @_;
my(@s) = qw(<TABLE><TR><TD>Datasource</TD><TD>Username</TD></TR>);
for (keys %Connected) {
push @s, '<TR><TD>', join('</TD><TD>', (split($;, $_))[0,1]), "</TD></TR>\n";
}
push @s, '</TABLE>';
return \@s;
}
) if ($INC{'Apache.pm'} and Apache->can('module') and Apache->module('Apache::Status'));
1;
__END__
=head1 NAME
Apache::DBI - Initiate a persistent database connection
=head1 SYNOPSIS
# Configuration in httpd.conf or startup.pl:
PerlModule Apache::DBI # this comes before all other modules using DBI
Do NOT change anything in your scripts. The usage of this module is
absolutely transparent !
=head1 DESCRIPTION
This module initiates a persistent database connection.
The database access uses Perl's DBI. For supported DBI drivers see:
http://dbi.perl.org/
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. The parameters defining the connection have
to be exactly the same, including the connect attributes! 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
remove the disconnect statements from your code. They won't do anything because
the Apache::DBI module overloads the disconnect method.
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
servers. Every server needs to do its own connect. It would be nice, if all
servers 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 create a database handle upon startup of the httpd and then inheriting this
handle to every subsequent server. This will cause clashes when the handle is
used by two processes at the same time.
With this limitation in mind, there are scenarios, where the usage of
Apache::DBI is depreciated. Think about a heavy loaded Web-site where every
user connects to the database with a unique userid. Every server 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 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 or you can deactivate the usage of the ping method
(see CONFIGURATION below).
Here is generalized ping method, which can be added to the driver module:
package DBD::xxx::db; # ====== DATABASE ======
use strict;
sub ping {
my ($dbh) = @_;
my $ret = 0;
eval {
local $SIG{__DIE__} = sub { return (0); };
local $SIG{__WARN__} = sub { return (0); };
# adapt the select statement to your database:
$ret = $dbh->do('select 1');
};
return ($@) ? 0 : $ret;
}
Transactions: a standard DBI script will automatically perform a rollback
whenever the script exits. In the case of persistent database connections,
the database handle will not be destroyed and hence no automatic rollback
occurs. At a first glance it seems even to be possible, to handle a transaction
over multiple requests. But this should be avoided, because different
requests are handled by different servers and a server does not know the state
of a specific transaction which has been started by another server. In general
it is good practice to perform an explicit commit or rollback at the end of
every script. In order to avoid inconsistencies in the database in case
AutoCommit is off and the script finishes without an explicit rollback, the
Apache::DBI module uses a PerlCleanupHandler to issue a rollback at the
end of every request. Note, that this CleanupHandler will only be used, if
the initial data_source sets AutoCommit = 0. It will not be used, if AutoCommit
will be turned off, after the connect has been done.
This module plugs in a menu item for Apache::Status. The menu lists the
current database connections. It should be considered incomplete because of
the limitations explained above. It shows the current database connections
for one specific server, the one which happens to serve the current request.
Other servers might have other database connections. The Apache::Status module
has to be loaded before the Apache::DBI module !
=head1 CONFIGURATION
The module should be loaded upon startup of the Apache daemon.
Add the following line to your httpd.conf or startup.pl:
PerlModule Apache::DBI
It is important, to load this module before any other modules using DBI !
A common usage is to load the module in a startup file via the PerlRequire
directive. See eg/startup.pl for an example.
There are two configurations which are server-specific and which can be done
upon server startup:
Apache::DBI->connect_on_init($data_source, $username, $auth, \%attr)
This can be used as a simple way to have apache servers establish connections
on process startup.
Apache::DBI->setPingTimeOut($data_source, $timeout)
This configures the usage of the ping method, to validate a connection.
Setting the timeout to 0 will always validate the database connection
using the ping method (default). Setting the timeout < 0 will de-activate
the validation of the database handle. This can be used for drivers, which
do not implement the ping-method. Setting the timeout > 0 will ping the
database only if the last access was more than timeout seconds before.
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.
To enable debugging the variable $Apache::DBI::DEBUG must be set. This
can either be done in startup.pl or in the user script. Setting the variable
to 1, just reports about a new connect. Setting the variable to 2 enables full
debug output.
=head1 PREREQUISITES
Note that this module needs mod_perl-1.08 or higher, apache_1.3.0 or higher
and that mod_perl needs to be configured with the appropriate call-back hooks:
PERL_CHILD_INIT=1 PERL_STACKED_HANDLERS=1.
=head1 MOD_PERL 2.0
Apache::DBI version 0.90_02 and later might work under mod_perl 2.0.
See the Changes file for more information. Beware that it has
only been tested very lightly.
=head1 SEE ALSO
L<Apache>, L<mod_perl>, L<DBI>
=head1 AUTHORS
=item *
Ask Bjoern Hansen <ask@develooper.com> is currently packaging new releases.
=item *
Edmund Mergl was the original author of Apache::DBI. It is now
supported and maintained by the modperl mailinglist, see the mod_perl
documentation for instructions on how to subscribe.
=item *
mod_perl by Doug MacEachern.
=item *
DBI by Tim Bunce <dbi-users-subscribe@perl.org>
=head1 COPYRIGHT
The Apache::DBI module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
=cut