DBIx::Class::Storage::User:ContributedDBIx::Class::Storage::DBI::Replicated(3)NAMEDBIx::Class::Storage::DBI::Replicated - BETA Replicated database
support
SYNOPSIS
The Following example shows how to change an existing $schema to a
replicated storage type, add some replicated (read-only) databases, and
perform reporting tasks.
You should set the 'storage_type attribute to a replicated type. You
should also define your arguments, such as which balancer you want and
any arguments that the Pool object should get.
my $schema = Schema::Class->clone;
$schema->storage_type( ['::DBI::Replicated', {balancer=>'::Random'}] );
$schema->connection(...);
Next, you need to add in the Replicants. Basically this is an array of
arrayrefs, where each arrayref is database connect information. Think
of these arguments as what you'd pass to the 'normal' $schema->connect
method.
$schema->storage->connect_replicants(
[$dsn1, $user, $pass, \%opts],
[$dsn2, $user, $pass, \%opts],
[$dsn3, $user, $pass, \%opts],
);
Now, just use the $schema as you normally would. Automatically all
reads will be delegated to the replicants, while writes to the master.
$schema->resultset('Source')->search({name=>'etc'});
You can force a given query to use a particular storage using the
search attribute 'force_pool'. For example:
my $RS = $schema->resultset('Source')->search(undef, {force_pool=>'master'});
Now $RS will force everything (both reads and writes) to use whatever
was setup as the master storage. 'master' is hardcoded to always point
to the Master, but you can also use any Replicant name. Please see:
DBIx::Class::Storage::DBI::Replicated::Pool and the replicants
attribute for more.
Also see transactions and "execute_reliably" for alternative ways to
force read traffic to the master. In general, you should wrap your
statements in a transaction when you are reading and writing to the
same tables at the same time, since your replicants will often lag a
bit behind the master.
See DBIx::Class::Storage::DBI::Replicated::Instructions for more help
and walkthroughs.
DESCRIPTION
Warning: This class is marked BETA. This has been running a production
website using MySQL native replication as its backend and we have some
decent test coverage but the code hasn't yet been stressed by a variety
of databases. Individual DBs may have quirks we are not aware of.
Please use this in first development and pass along your
experiences/bug fixes.
This class implements replicated data store for DBI. Currently you can
define one master and numerous slave database connections. All write-
type queries (INSERT, UPDATE, DELETE and even LAST_INSERT_ID) are
routed to master database, all read-type queries (SELECTs) go to the
slave database.
Basically, any method request that DBIx::Class::Storage::DBI would
normally handle gets delegated to one of the two attributes:
"read_handler" or to "write_handler". Additionally, some methods need
to be distributed to all existing storages. This way our storage class
is a drop in replacement for DBIx::Class::Storage::DBI.
Read traffic is spread across the replicants (slaves) occurring to a
user selected algorithm. The default algorithm is random weighted.
NOTES
The consistency between master and replicants is database specific.
The Pool gives you a method to validate its replicants, removing and
replacing them when they fail/pass predefined criteria. Please make
careful use of the ways to force a query to run against Master when
needed.
REQUIREMENTS
Replicated Storage has additional requirements not currently part of
DBIx::Class. See DBIx::Class::Optional::Dependencies for more details.
ATTRIBUTES
This class defines the following attributes.
schema
The underlying DBIx::Class::Schema object this storage is attaching
pool_type
Contains the classname which will instantiate the "pool" object.
Defaults to: DBIx::Class::Storage::DBI::Replicated::Pool.
pool_args
Contains a hashref of initialized information to pass to the Balancer
object. See DBIx::Class::Storage::DBI::Replicated::Pool for available
arguments.
balancer_type
The replication pool requires a balance class to provider the methods
for choose how to spread the query load across each replicant in the
pool.
balancer_args
Contains a hashref of initialized information to pass to the Balancer
object. See DBIx::Class::Storage::DBI::Replicated::Balancer for
available arguments.
pool
Is a DBIx::Class::Storage::DBI::Replicated::Pool or derived class.
This is a container class for one or more replicated databases.
balancer
Is a DBIx::Class::Storage::DBI::Replicated::Balancer or derived class.
This is a class that takes a pool
(DBIx::Class::Storage::DBI::Replicated::Pool)
master
The master defines the canonical state for a pool of connected
databases. All the replicants are expected to match this databases
state. Thus, in a classic Master / Slaves distributed system, all the
slaves are expected to replicate the Master's state as quick as
possible. This is the only database in the pool of databases that is
allowed to handle write traffic.
ATTRIBUTES IMPLEMENTING THE DBIx::Storage::DBI INTERFACE
The following methods are delegated all the methods required for the
DBIx::Class::Storage::DBI interface.
read_handler
Defines an object that implements the read side of
BIx::Class::Storage::DBI.
write_handler
Defines an object that implements the write side of
BIx::Class::Storage::DBI, as well as methods that don't write or read
that can be called on only one storage, methods that return a $dbh, and
any methods that don't make sense to run on a replicant.
around: connect_info
Preserves master's "connect_info" options (for merging with
replicants.) Also sets any Replicated-related options from
connect_info, such as "pool_type", "pool_args", "balancer_type" and
"balancer_args".
METHODS
This class defines the following methods.
BUILDARGS
DBIx::Class::Schema when instantiating its storage passed itself as the
first argument. So we need to massage the arguments a bit so that all
the bits get put into the correct places.
_build_master
Lazy builder for the "master" attribute.
_build_pool
Lazy builder for the "pool" attribute.
_build_balancer
Lazy builder for the "balancer" attribute. This takes a Pool object so
that the balancer knows which pool it's balancing.
_build_write_handler
Lazy builder for the "write_handler" attribute. The default is to set
this to the "master".
_build_read_handler
Lazy builder for the "read_handler" attribute. The default is to set
this to the "balancer".
around: connect_replicants
All calls to connect_replicants needs to have an existing $schema
tacked onto top of the args, since DBIx::Storage::DBI needs it, and any
"connect_info" options merged with the master, with replicant opts
having higher priority.
all_storages
Returns an array of of all the connected storage backends. The first
element in the returned array is the master, and the remainings are
each of the replicants.
execute_reliably ($coderef, ?@args)
Given a coderef, saves the current state of the "read_handler", forces
it to use reliable storage (e.g. sets it to the master), executes a
coderef and then restores the original state.
Example:
my $reliably = sub {
my $name = shift @_;
$schema->resultset('User')->create({name=>$name});
my $user_rs = $schema->resultset('User')->find({name=>$name});
return $user_rs;
};
my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
Use this when you must be certain of your database state, such as when
you just inserted something and need to get a resultset including it,
etc.
set_reliable_storage
Sets the current $schema to be 'reliable', that is all queries, both
read and write are sent to the master
set_balanced_storage
Sets the current $schema to be use the </balancer> for all reads, while
all writes are sent to the master only
connected
Check that the master and at least one of the replicants is connected.
ensure_connected
Make sure all the storages are connected.
limit_dialect
Set the limit_dialect for all existing storages
quote_char
Set the quote_char for all existing storages
name_sep
Set the name_sep for all existing storages
set_schema
Set the schema object for all existing storages
debug
set a debug flag across all storages
debugobj
set a debug object
debugfh
set a debugfh object
debugcb
set a debug callback
disconnect
disconnect everything
cursor_class
set cursor class on all storages, or return master's
cursor
set cursor class on all storages, or return master's, alias for
"cursor_class" above.
unsafe
sets the "unsafe" in DBIx::Class::Storage::DBI option on all storages
or returns master's current setting
disable_sth_caching
sets the "disable_sth_caching" in DBIx::Class::Storage::DBI option on
all storages or returns master's current setting
lag_behind_master
returns the highest Replicant "lag_behind_master" in
DBIx::Class::Storage::DBI setting
is_replicating
returns true if all replicants return true for "is_replicating" in
DBIx::Class::Storage::DBI
connect_call_datetime_setup
calls "connect_call_datetime_setup" in DBIx::Class::Storage::DBI for
all storages
GOTCHAS
Due to the fact that replicants can lag behind a master, you must take
care to make sure you use one of the methods to force read queries to a
master should you need realtime data integrity. For example, if you
insert a row, and then immediately re-read it from the database (say,
by doing $row->discard_changes) or you insert a row and then
immediately build a query that expects that row to be an item, you
should force the master to handle reads. Otherwise, due to the lag,
there is no certainty your data will be in the expected state.
For data integrity, all transactions automatically use the master
storage for all read and write queries. Using a transaction is the
preferred and recommended method to force the master to handle all read
queries.
Otherwise, you can force a single query to use the master with the
'force_pool' attribute:
my $row = $resultset->search(undef, {force_pool=>'master'})->find($pk);
This attribute will safely be ignore by non replicated storages, so you
can use the same code for both types of systems.
Lastly, you can use the "execute_reliably" method, which works very
much like a transaction.
For debugging, you can turn replication on/off with the methods
"set_reliable_storage" and "set_balanced_storage", however this
operates at a global level and is not suitable if you have a shared
Schema object being used by multiple processes, such as on a web
application server. You can get around this limitation by using the
Schema clone method.
my $new_schema = $schema->clone;
$new_schema->set_reliable_storage;
## $new_schema will use only the Master storage for all reads/writes while
## the $schema object will use replicated storage.
AUTHOR
John Napiorkowski <john.napiorkowski@takkle.com>
Based on code originated by:
Norbert CsongrA~Xdi <bert@cpan.org>
Peter SiklA~Xsi <einon@einon.hu>
LICENSE
You may distribute this code under the same terms as Perl itself.
perl v5.14.22012DBIx::Class::Storage::DBI::Replicated(3)