Perl Connection Pooling - mysql

Question

Right now we have a large perl application that is using raw DBI to connect to MySQL and execute SQL statements. It creates a connection each time and terminates. Were starting to approach mysql's connection limit (200 at once)
It looks like DBIx::Connection supports application layer connection pooling.
Has anybody had any experience with DBIx::Connection?. Are there any other considerations for connection pooling?
I also see mod_dbd which is an Apache mod that looks like it handles connection pooling.
http://httpd.apache.org/docs/2.1/mod/mod_dbd.html

Answer 1

I don't have any experience with DBIx::Connection, but I use DBIx::Connector (essentially what DBIx::Class uses internally, but inlined) and it's wonderful...
I pool these connections with a Moose object wrapper that hands back existing object instances if the connection parameters are identical (this would work the same for any underlying DB object):
package MyApp::Factory::DatabaseConnection;
use strict;
use warnings;
use Moose;
# table of database name -> connection objects
has connection_pool => (
is => 'ro', isa => 'HashRef[DBIx::Connector]',
traits => ['Hash'],
handles => {
has_pooled_connection => 'exists',
get_pooled_connection => 'get',
save_pooled_connection => 'set',
},
default => sub { {} },
);
sub get_connection
{
my ($self, %options) = #_;
# some application-specific parsing of %options here...
my $obj;
if ($options{reuse})
{
# extract the last-allocated connection for this database and pass it
# back, if there is one.
$obj = $self->get_pooled_connection($options{database});
}
if (not $obj or not $obj->connected)
{
# look up connection info based on requested database name
my ($dsn, $username, $password) = $self->get_connection_info($options{database});
$obj = DBIx::Connector->new($dsn, $username, $password);
return unless $obj;
# Save this connection for later reuse, possibly replacing an earlier
# saved connection (this latest one has the highest chance of being in
# the same pid as a subsequent request).
$self->save_pooled_connection($options{database}, $obj) unless $options{nosave};
}
return $obj;
}

Answer 2

Just making sure: you know about DBI->connect_cached(), right? It's a drop-in replacement for connect() that reuses dbh's, where possible, over the life of your perl script. Maybe your problem is solvable by adding 7 characters :)
And, MySQL's connections are relatively cheap. Running with your DB at max_connections=1000 or more won't by itself cause problems. (If your clients are demanding more work than your DB can handle, that's a more serious problem, one which a lower max_connections might put off but of course not solve.)