This is an introductory document for L<DBIx::Class::Storage::Replication>.
This document is not an overview of what replication is or why you should be
-using it. It is not a document explaing how to setup MySQL native replication
-either. Copious external resources are avialable for both. This document
+using it. It is not a document explaining how to setup MySQL native replication
+either. Copious external resources are available for both. This document
presumes you have the basics down.
-
+
=head1 DESCRIPTION
L<DBIx::Class> supports a framework for using database replication. This system
-is integrated completely, which means once it's setup you should be able to
+is integrated completely, which means once it's setup you should be able to
automatically just start using a replication cluster without additional work or
changes to your code. Some caveats apply, primarily related to the proper use
of transactions (you are wrapping all your database modifying statements inside
For an easy way to start playing with MySQL native replication, see:
L<MySQL::Sandbox>.
-If you are using this with a L<Catalyst> based appplication, you may also wish
-to see more recent updates to L<Catalyst::Model::DBIC::Schema>, which has
+If you are using this with a L<Catalyst> based application, you may also want
+to see more recent updates to L<Catalyst::Model::DBIC::Schema>, which has
support for replication configuration options as well.
=head1 REPLICATED STORAGE
By default, when you start L<DBIx::Class>, your Schema (L<DBIx::Class::Schema>)
is assigned a storage_type, which when fully connected will reflect your
-underlying storage engine as defined by your choosen database driver. For
+underlying storage engine as defined by your chosen database driver. For
example, if you connect to a MySQL database, your storage_type will be
-L<DBIx::Class::Storage::DBI::mysql> Your storage type class will contain
+L<DBIx::Class::Storage::DBI::mysql> Your storage type class will contain
database specific code to help smooth over the differences between databases
and let L<DBIx::Class> do its thing.
If you want to use replication, you will override this setting so that the
-replicated storage engine will 'wrap' your underlying storages and present to
-the end programmer a unified interface. This wrapper storage class will
+replicated storage engine will 'wrap' your underlying storages and present
+a unified interface to the end programmer. This wrapper storage class will
delegate method calls to either a master database or one or more replicated
databases based on if they are read only (by default sent to the replicants)
-or write (reserved for the master). Additionally, the Replicated storage
+or write (reserved for the master). Additionally, the Replicated storage
will monitor the health of your replicants and automatically drop them should
one exceed configurable parameters. Later, it can automatically restore a
replicant when its health is restored.
a transaction, replicated storage will automatically delegate all database
traffic to the master storage. There are several ways to enable this high
integrity mode, but wrapping your statements inside a transaction is the easy
-and canonical option.
+and canonical option.
=head1 PARTS OF REPLICATED STORAGE
A replicated storage contains several parts. First, there is the replicated
-storage itself (L<DBIx::Class::Storage::DBI::Replicated). A replicated storage
+storage itself (L<DBIx::Class::Storage::DBI::Replicated>). A replicated storage
takes a pool of replicants (L<DBIx::Class::Storage::DBI::Replicated::Pool>)
-and a software balancer (L<DBIx::Class::Storage::DBI::Replicated::Pool>). The
-balancer does the job of splitting up all the read traffic amongst each
-replicant in the Pool. Currently there are two types of balancers, a Random one
+and a software balancer (L<DBIx::Class::Storage::DBI::Replicated::Balancer>).
+The balancer does the job of splitting up all the read traffic amongst the
+replicants in the Pool. Currently there are two types of balancers, a Random one
which chooses a Replicant in the Pool using a naive randomizer algorithm, and a
First replicant, which just uses the first one in the Pool (and obviously is
only of value when you have a single replicant).
you use (or upgrade to) the latest L<Catalyst::Model::DBIC::Schema>, which makes
this job even easier.
-First, you need to connect your L<DBIx::Class::Schema>. Let's assume you have
-such a schema called, "MyApp::Schema".
+First, you need to get a C<$schema> object and set the storage_type:
- use MyApp::Schema;
- my $schema = MyApp::Schema->connect($dsn, $user, $pass);
+ my $schema = MyApp::Schema->clone;
+ $schema->storage_type([
+ '::DBI::Replicated' => {
+ balancer_type => '::Random',
+ balancer_args => {
+ auto_validate_every => 5,
+ master_read_weight => 1
+ },
+ pool_args => {
+ maximum_lag =>2,
+ },
+ }
+ ]);
-Next, you need to set the storage_type.
+Then, you need to connect your L<DBIx::Class::Schema>.
- $schema->storage_type(
- ::DBI::Replicated' => {
- balancer_type => '::Random',
- balancer_args => {
- auto_validate_every => 5,
- master_read_weight => 1
- },
- pool_args => {
- maximum_lag =>2,
- },
- }
- );
+ $schema->connection($dsn, $user, $pass);
Let's break down the settings. The method L<DBIx::Class::Schema/storage_type>
takes one mandatory parameter, a scalar value, and an option second value which
'balancer_args' get passed to the balancer when it's instantiated. All
balancers have the 'auto_validate_every' option. This is the number of seconds
we allow to pass between validation checks on a load balanced replicant. So
-the higher the number, the more possibility that your reads to the replicant
-may be inconsistant with what's on the master. Setting this number too low
+the higher the number, the more possibility that your reads to the replicant
+may be inconsistent with what's on the master. Setting this number too low
will result in increased database loads, so choose a number with care. Our
experience is that setting the number around 5 seconds results in a good
performance / integrity balance.
This object (L<DBIx::Class::Storage::DBI::Replicated::Pool>) manages all the
declared replicants. 'maximum_lag' is the number of seconds a replicant is
allowed to lag behind the master before being temporarily removed from the pool.
-Keep in mind that the Balancer option 'auto_validate_every' determins how often
+Keep in mind that the Balancer option 'auto_validate_every' determines how often
a replicant is tested against this condition, so the true possible lag can be
higher than the number you set. The default is zero.
No matter how low you set the maximum_lag or the auto_validate_every settings,
there is always the chance that your replicants will lag a bit behind the
master for the supported replication system built into MySQL. You can ensure
-reliabily reads by using a transaction, which will force both read and write
+reliable reads by using a transaction, which will force both read and write
activity to the master, however this will increase the load on your master
database.
After you've configured the replicated storage, you need to add the connection
information for the replicants:
- $schema->storage->connect_replicants(
- [$dsn1, $user, $pass, \%opts],
- [$dsn2, $user, $pass, \%opts],
- [$dsn3, $user, $pass, \%opts],
- );
+ $schema->storage->connect_replicants(
+ [$dsn1, $user, $pass, \%opts],
+ [$dsn2, $user, $pass, \%opts],
+ [$dsn3, $user, $pass, \%opts],
+ );
These replicants should be configured as slaves to the master using the
instructions for MySQL native replication, or if you are just learning, you
projects / dbsrgits/DBIx-Class.git / blobdiff