1 package DBIx::Class::Storage::DBI::Replicated;
4 use Carp::Clan qw/^DBIx::Class/;
6 ## Modules required for Replication support not required for general DBIC
7 ## use, so we explicitly test for these.
9 my %replication_required = (
11 MooseX::AttributeHelpers => '0.12',
12 MooseX::Types => '0.10',
13 namespace::clean => '0.11',
18 for my $module (keys %replication_required) {
19 eval "use $module $replication_required{$module}";
20 push @didnt_load, "$module $replication_required{$module}"
24 croak("@{[ join ', ', @didnt_load ]} are missing and are required for Replication")
28 use DBIx::Class::Storage::DBI;
29 use DBIx::Class::Storage::DBI::Replicated::Pool;
30 use DBIx::Class::Storage::DBI::Replicated::Balancer;
31 use DBIx::Class::Storage::DBI::Replicated::Types 'BalancerClassNamePart';
32 use MooseX::Types::Moose qw/ClassName HashRef Object/;
34 use namespace::clean -except => 'meta';
38 DBIx::Class::Storage::DBI::Replicated - BETA Replicated database support
42 The Following example shows how to change an existing $schema to a replicated
43 storage type, add some replicated (readonly) databases, and perform reporting
46 ## Change storage_type in your schema class
47 $schema->storage_type( ['::DBI::Replicated', {balancer=>'::Random'}] );
49 ## Add some slaves. Basically this is an array of arrayrefs, where each
50 ## arrayref is database connect information
52 $schema->storage->connect_replicants(
53 [$dsn1, $user, $pass, \%opts],
54 [$dsn2, $user, $pass, \%opts],
55 [$dsn3, $user, $pass, \%opts],
58 ## Now, just use the $schema as normal
59 $schema->resultset('Source')->search({name=>'etc'});
61 ## You can force a given query to use a particular storage using the search
62 ### attribute 'force_pool'. For example:
64 my $RS = $schema->resultset('Source')->search(undef, {force_pool=>'master'});
66 ## Now $RS will force everything (both reads and writes) to use whatever was
67 ## setup as the master storage. 'master' is hardcoded to always point to the
68 ## Master, but you can also use any Replicant name. Please see:
69 ## L<DBIx::Class::Storage::Replicated::Pool> and the replicants attribute for
70 ## More. Also see transactions and L</execute_reliably> for alternative ways
71 ## to force read traffic to the master.
75 Warning: This class is marked BETA. This has been running a production
76 website using MySQL native replication as its backend and we have some decent
77 test coverage but the code hasn't yet been stressed by a variety of databases.
78 Individual DB's may have quirks we are not aware of. Please use this in first
79 development and pass along your experiences/bug fixes.
81 This class implements replicated data store for DBI. Currently you can define
82 one master and numerous slave database connections. All write-type queries
83 (INSERT, UPDATE, DELETE and even LAST_INSERT_ID) are routed to master
84 database, all read-type queries (SELECTs) go to the slave database.
86 Basically, any method request that L<DBIx::Class::Storage::DBI> would normally
87 handle gets delegated to one of the two attributes: L</read_handler> or to
88 L</write_handler>. Additionally, some methods need to be distributed
89 to all existing storages. This way our storage class is a drop in replacement
90 for L<DBIx::Class::Storage::DBI>.
92 Read traffic is spread across the replicants (slaves) occuring to a user
93 selected algorithm. The default algorithm is random weighted.
97 The consistancy betweeen master and replicants is database specific. The Pool
98 gives you a method to validate it's replicants, removing and replacing them
99 when they fail/pass predefined criteria. Please make careful use of the ways
100 to force a query to run against Master when needed.
104 Replicated Storage has additional requirements not currently part of L<DBIx::Class>
107 MooseX::AttributeHelpers => 0.12
108 MooseX::Types => 0.10
109 namespace::clean => 0.11
111 You will need to install these modules manually via CPAN or make them part of the
112 Makefile for your distribution.
116 This class defines the following attributes.
120 The underlying L<DBIx::Class::Schema> object this storage is attaching
126 isa=>'DBIx::Class::Schema',
133 Contains the classname which will instantiate the L</pool> object. Defaults
134 to: L<DBIx::Class::Storage::DBI::Replicated::Pool>.
142 default=>'DBIx::Class::Storage::DBI::Replicated::Pool',
144 'create_pool' => 'new',
150 Contains a hashref of initialized information to pass to the Balancer object.
151 See L<DBIx::Class::Storage::Replicated::Pool> for available arguments.
166 The replication pool requires a balance class to provider the methods for
167 choose how to spread the query load across each replicant in the pool.
171 has 'balancer_type' => (
173 isa=>BalancerClassNamePart,
176 default=> 'DBIx::Class::Storage::DBI::Replicated::Balancer::First',
178 'create_balancer' => 'new',
184 Contains a hashref of initialized information to pass to the Balancer object.
185 See L<DBIx::Class::Storage::Replicated::Balancer> for available arguments.
189 has 'balancer_args' => (
199 Is a <DBIx::Class::Storage::DBI::Replicated::Pool> or derived class. This is a
200 container class for one or more replicated databases.
206 isa=>'DBIx::Class::Storage::DBI::Replicated::Pool',
217 Is a <DBIx::Class::Storage::DBI::Replicated::Balancer> or derived class. This
218 is a class that takes a pool (<DBIx::Class::Storage::DBI::Replicated::Pool>)
224 isa=>'DBIx::Class::Storage::DBI::Replicated::Balancer',
226 handles=>[qw/auto_validate_every/],
231 The master defines the canonical state for a pool of connected databases. All
232 the replicants are expected to match this databases state. Thus, in a classic
233 Master / Slaves distributed system, all the slaves are expected to replicate
234 the Master's state as quick as possible. This is the only database in the
235 pool of databases that is allowed to handle write traffic.
241 isa=>'DBIx::Class::Storage::DBI',
245 =head1 ATTRIBUTES IMPLEMENTING THE DBIx::Storage::DBI INTERFACE
247 The following methods are delegated all the methods required for the
248 L<DBIx::Class::Storage::DBI> interface.
252 Defines an object that implements the read side of L<BIx::Class::Storage::DBI>.
256 has 'read_handler' => (
269 Defines an object that implements the write side of L<BIx::Class::Storage::DBI>.
273 has 'write_handler' => (
286 deployment_statements
302 with_deferred_fk_checks
312 This class defines the following methods.
316 L<DBIx::Class::Schema> when instantiating it's storage passed itself as the
317 first argument. So we need to massage the arguments a bit so that all the
318 bits get put into the correct places.
323 my ($class, $schema, $storage_type_args, @args) = @_;
334 Lazy builder for the L</master> attribute.
340 DBIx::Class::Storage::DBI->new($self->schema);
345 Lazy builder for the L</pool> attribute.
351 $self->create_pool(%{$self->pool_args});
354 =head2 _build_balancer
356 Lazy builder for the L</balancer> attribute. This takes a Pool object so that
357 the balancer knows which pool it's balancing.
361 sub _build_balancer {
363 $self->create_balancer(
365 master=>$self->master,
366 %{$self->balancer_args},
370 =head2 _build_write_handler
372 Lazy builder for the L</write_handler> attribute. The default is to set this to
377 sub _build_write_handler {
378 return shift->master;
381 =head2 _build_read_handler
383 Lazy builder for the L</read_handler> attribute. The default is to set this to
388 sub _build_read_handler {
389 return shift->balancer;
392 =head2 around: connect_replicants
394 All calls to connect_replicants needs to have an existing $schema tacked onto
395 top of the args, since L<DBIx::Storage::DBI> needs it.
399 around 'connect_replicants' => sub {
400 my ($method, $self, @args) = @_;
401 $self->$method($self->schema, @args);
406 Returns an array of of all the connected storage backends. The first element
407 in the returned array is the master, and the remainings are each of the
414 return grep {defined $_ && blessed $_} (
416 values %{ $self->replicants },
420 =head2 execute_reliably ($coderef, ?@args)
422 Given a coderef, saves the current state of the L</read_handler>, forces it to
423 use reliable storage (ie sets it to the master), executes a coderef and then
424 restores the original state.
430 $schema->resultset('User')->create({name=>$name});
431 my $user_rs = $schema->resultset('User')->find({name=>$name});
435 my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
437 Use this when you must be certain of your database state, such as when you just
438 inserted something and need to get a resultset including it, etc.
442 sub execute_reliably {
443 my ($self, $coderef, @args) = @_;
445 unless( ref $coderef eq 'CODE') {
446 $self->throw_exception('Second argument must be a coderef');
449 ##Get copy of master storage
450 my $master = $self->master;
452 ##Get whatever the current read hander is
453 my $current = $self->read_handler;
455 ##Set the read handler to master
456 $self->read_handler($master);
458 ## do whatever the caller needs
460 my $want_array = wantarray;
464 @result = $coderef->(@args);
465 } elsif(defined $want_array) {
466 ($result[0]) = ($coderef->(@args));
472 ##Reset to the original state
473 $self->read_handler($current);
475 ##Exception testing has to come last, otherwise you might leave the
476 ##read_handler set to master.
479 $self->throw_exception("coderef returned an error: $@");
481 return $want_array ? @result : $result[0];
485 =head2 set_reliable_storage
487 Sets the current $schema to be 'reliable', that is all queries, both read and
488 write are sent to the master
492 sub set_reliable_storage {
494 my $schema = $self->schema;
495 my $write_handler = $self->schema->storage->write_handler;
497 $schema->storage->read_handler($write_handler);
500 =head2 set_balanced_storage
502 Sets the current $schema to be use the </balancer> for all reads, while all
503 writea are sent to the master only
507 sub set_balanced_storage {
509 my $schema = $self->schema;
510 my $write_handler = $self->schema->storage->balancer;
512 $schema->storage->read_handler($write_handler);
515 =head2 around: txn_do ($coderef)
517 Overload to the txn_do method, which is delegated to whatever the
518 L<write_handler> is set to. We overload this in order to wrap in inside a
519 L</execute_reliably> method.
523 around 'txn_do' => sub {
524 my($txn_do, $self, $coderef, @args) = @_;
525 $self->execute_reliably(sub {$self->$txn_do($coderef, @args)});
530 Check that the master and at least one of the replicants is connected.
537 $self->master->connected &&
538 $self->pool->connected_replicants;
541 =head2 ensure_connected
543 Make sure all the storages are connected.
547 sub ensure_connected {
549 foreach my $source ($self->all_storages) {
550 $source->ensure_connected(@_);
556 Set the limit_dialect for all existing storages
562 foreach my $source ($self->all_storages) {
563 $source->limit_dialect(@_);
565 return $self->master->quote_char;
570 Set the quote_char for all existing storages
576 foreach my $source ($self->all_storages) {
577 $source->quote_char(@_);
579 return $self->master->quote_char;
584 Set the name_sep for all existing storages
590 foreach my $source ($self->all_storages) {
591 $source->name_sep(@_);
593 return $self->master->name_sep;
598 Set the schema object for all existing storages
604 foreach my $source ($self->all_storages) {
605 $source->set_schema(@_);
611 set a debug flag across all storages
618 foreach my $source ($self->all_storages) {
622 return $self->master->debug;
627 set a debug object across all storages
634 foreach my $source ($self->all_storages) {
635 $source->debugobj(@_);
638 return $self->master->debugobj;
643 set a debugfh object across all storages
650 foreach my $source ($self->all_storages) {
651 $source->debugfh(@_);
654 return $self->master->debugfh;
659 set a debug callback across all storages
666 foreach my $source ($self->all_storages) {
667 $source->debugcb(@_);
670 return $self->master->debugcb;
675 disconnect everything
681 foreach my $source ($self->all_storages) {
682 $source->disconnect(@_);
688 Due to the fact that replicants can lag behind a master, you must take care to
689 make sure you use one of the methods to force read queries to a master should
690 you need realtime data integrity. For example, if you insert a row, and then
691 immediately re-read it from the database (say, by doing $row->discard_changes)
692 or you insert a row and then immediately build a query that expects that row
693 to be an item, you should force the master to handle reads. Otherwise, due to
694 the lag, there is no certainty your data will be in the expected state.
696 For data integrity, all transactions automatically use the master storage for
697 all read and write queries. Using a transaction is the preferred and recommended
698 method to force the master to handle all read queries.
700 Otherwise, you can force a single query to use the master with the 'force_pool'
703 my $row = $resultset->search(undef, {force_pool=>'master'})->find($pk);
705 This attribute will safely be ignore by non replicated storages, so you can use
706 the same code for both types of systems.
708 Lastly, you can use the L</execute_reliably> method, which works very much like
711 For debugging, you can turn replication on/off with the methods L</set_reliable_storage>
712 and L</set_balanced_storage>, however this operates at a global level and is not
713 suitable if you have a shared Schema object being used by multiple processes,
714 such as on a web application server. You can get around this limitation by
715 using the Schema clone method.
717 my $new_schema = $schema->clone;
718 $new_schema->set_reliable_storage;
720 ## $new_schema will use only the Master storage for all reads/writes while
721 ## the $schema object will use replicated storage.
725 John Napiorkowski <john.napiorkowski@takkle.com>
727 Based on code originated by:
729 Norbert Csongrádi <bert@cpan.org>
730 Peter Siklósi <einon@einon.hu>
734 You may distribute this code under the same terms as Perl itself.
738 __PACKAGE__->meta->make_immutable;