package DBIx::Class::Storage::DBI::Replicated::Balancer;
use Moose;
-use List::Util qw(shuffle);
=head1 NAME
This class defines the following attributes.
+=head2 master
+
+The L<DBIx::Class::Storage::DBI> object that is the master database all the
+replicants are trying to follow. The balancer needs to know it since it's the
+ultimate fallback.
+
+=cut
+
+has 'master' => (
+ is=>'ro',
+ isa=>'DBIx::Class::Storage::DBI',
+ required=>1,
+);
+
+=head2 pool
+
+The L<DBIx::Class::Storage::DBI::Replicated::Pool> object that we are trying to
+balance.
+
+=cut
+
+has 'pool' => (
+ is=>'ro',
+ isa=>'DBIx::Class::Storage::DBI::Replicated::Pool',
+ required=>1,
+);
+
+=head2 current_replicant
+
+Replicant storages (slaves) handle all read only traffic. The assumption is
+that your database will become readbound well before it becomes write bound
+and that being able to spread your read only traffic around to multiple
+databases is going to help you to scale traffic.
+
+This attribute returns the next slave to handle a read request. Your L</pool>
+attribute has methods to help you shuffle through all the available replicants
+via it's balancer object.
+
+=cut
+
+has 'current_replicant' => (
+ is=> 'rw',
+ isa=>'DBIx::Class::Storage::DBI',
+ lazy_build=>1,
+ handles=>[qw/
+ select
+ select_single
+ columns_info_for
+ /],
+);
+
=head1 METHODS
This class defines the following methods.
-=head2 next_storage ($pool)
+=head2 _build_current_replicant
+
+Lazy builder for the L</current_replicant_storage> attribute.
+
+=cut
+
+sub _build_current_replicant {
+ my $self = shift @_;
+ $self->next_storage;
+}
+
+=head2 next_storage
Given a pool object, return the next replicant that will serve queries. The
-default behavior is to randomize but you can write your own subclasses of
-L<DBIx::Class::Storage::DBI::Replicated::Balancer> to support other balance
-systems.
+default behavior is to grap the first replicant it finds but you can write
+your own subclasses of L<DBIx::Class::Storage::DBI::Replicated::Balancer> to
+support other balance systems.
+
+This returns from the pool of active replicants. If there are no active
+replicants, then you should have it return the master as an ultimate fallback.
=cut
sub next_storage {
my $self = shift @_;
- my $pool = shift @_;
-
- return (shuffle($pool->all_replicants))[0];
+ my $next = ($self->pool->active_replicants)[0];
+ return $next ? $next:$self->master;
}
+=head2 before: select
+
+Advice on the select attribute. Each time we use a replicant
+we need to change it via the storage pool algorithm. That way we are spreading
+the load evenly (hopefully) across existing capacity.
+
+=cut
+
+before 'select' => sub {
+ my $self = shift @_;
+ my $next_replicant = $self->next_storage;
+ $self->current_replicant($next_replicant);
+};
+
+=head2 before: select_single
+
+Advice on the select_single attribute. Each time we use a replicant
+we need to change it via the storage pool algorithm. That way we are spreading
+the load evenly (hopefully) across existing capacity.
+
+=cut
+
+before 'select_single' => sub {
+ my $self = shift @_;
+ my $next_replicant = $self->next_storage;
+ $self->current_replicant($next_replicant);
+};
+
+=head2 before: columns_info_for
+
+Advice on the current_replicant_storage attribute. Each time we use a replicant
+we need to change it via the storage pool algorithm. That way we are spreading
+the load evenly (hopefully) across existing capacity.
+
+=cut
+
+before 'columns_info_for' => sub {
+ my $self = shift @_;
+ my $next_replicant = $self->next_storage;
+ $self->current_replicant($next_replicant);
+};
=head1 AUTHOR
=cut
-1;
\ No newline at end of file
+1;