NAME
DBIx::Class::Storage::DBI::Replicated::Balancer - A Software Load Balancer
SYNOPSIS
This role is used internally by DBIx::Class::Storage::DBI::Replicated.
DESCRIPTION
Given a pool (DBIx::Class::Storage::DBI::Replicated::Pool) of replicated database's (DBIx::Class::Storage::DBI::Replicated::Replicant), defines a method by which query load can be spread out across each replicant in the pool.
ATTRIBUTES
This class defines the following attributes.
auto_validate_every ($seconds)
If auto_validate has some sort of value, run the validate_replicants every $seconds. Be careful with this, because if you set it to 0 you will end up validating every query.
master
The 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.
pool
The DBIx::Class::Storage::DBI::Replicated::Pool object that we are trying to balance.
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 "pool" attribute has methods to help you shuffle through all the available replicants via its balancer object.
METHODS
This class defines the following methods.
_build_current_replicant
Lazy builder for the "current_replicant_storage" attribute.
next_storage
This method should be defined in the class which consumes this role.
Given a pool object, return the next replicant that will serve queries. The default behavior is to grab the first replicant it finds but you can write your own subclasses of 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.
around: next_storage
Advice on next storage to add the autovalidation. We have this broken out so that it's easier to break out the auto validation into a role.
This also returns the master in the case that none of the replicants are active or just just forgot to create them :)
increment_storage
Rolls the Storage to whatever is next in the queue, as defined by the Balancer.
around: 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.
around: 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.
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.
_get_forced_pool ($name)
Given an identifier, find the most correct storage object to handle the query.
AUTHOR
John Napiorkowski <jjnapiork@cpan.org>
LICENSE
You may distribute this code under the same terms as Perl itself.