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::Types' => '0.16',
12 'namespace::clean' => '0.11',
13 'Hash::Merge' => '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")
29 use DBIx::Class::Storage::DBI;
30 use DBIx::Class::Storage::DBI::Replicated::Pool;
31 use DBIx::Class::Storage::DBI::Replicated::Balancer;
32 use DBIx::Class::Storage::DBI::Replicated::Types qw/BalancerClassNamePart DBICSchema DBICStorageDBI/;
33 use MooseX::Types::Moose qw/ClassName HashRef Object/;
34 use Scalar::Util 'reftype';
35 use Hash::Merge 'merge';
37 use namespace::clean -except => 'meta';
41 DBIx::Class::Storage::DBI::Replicated - BETA Replicated database support
45 The Following example shows how to change an existing $schema to a replicated
46 storage type, add some replicated (readonly) databases, and perform reporting
49 You should set the 'storage_type attribute to a replicated type. You should
50 also define your arguments, such as which balancer you want and any arguments
51 that the Pool object should get.
53 $schema->storage_type( ['::DBI::Replicated', {balancer=>'::Random'}] );
55 Next, you need to add in the Replicants. Basically this is an array of
56 arrayrefs, where each arrayref is database connect information. Think of these
57 arguments as what you'd pass to the 'normal' $schema->connect method.
59 $schema->storage->connect_replicants(
60 [$dsn1, $user, $pass, \%opts],
61 [$dsn2, $user, $pass, \%opts],
62 [$dsn3, $user, $pass, \%opts],
65 Now, just use the $schema as you normally would. Automatically all reads will
66 be delegated to the replicants, while writes to the master.
68 $schema->resultset('Source')->search({name=>'etc'});
70 You can force a given query to use a particular storage using the search
71 attribute 'force_pool'. For example:
73 my $RS = $schema->resultset('Source')->search(undef, {force_pool=>'master'});
75 Now $RS will force everything (both reads and writes) to use whatever was setup
76 as the master storage. 'master' is hardcoded to always point to the Master,
77 but you can also use any Replicant name. Please see:
78 L<DBIx::Class::Storage::DBI::Replicated::Pool> and the replicants attribute for more.
80 Also see transactions and L</execute_reliably> for alternative ways to
81 force read traffic to the master. In general, you should wrap your statements
82 in a transaction when you are reading and writing to the same tables at the
83 same time, since your replicants will often lag a bit behind the master.
85 See L<DBIx::Class::Storage::DBI::Replicated::Instructions> for more help and
90 Warning: This class is marked BETA. This has been running a production
91 website using MySQL native replication as its backend and we have some decent
92 test coverage but the code hasn't yet been stressed by a variety of databases.
93 Individual DB's may have quirks we are not aware of. Please use this in first
94 development and pass along your experiences/bug fixes.
96 This class implements replicated data store for DBI. Currently you can define
97 one master and numerous slave database connections. All write-type queries
98 (INSERT, UPDATE, DELETE and even LAST_INSERT_ID) are routed to master
99 database, all read-type queries (SELECTs) go to the slave database.
101 Basically, any method request that L<DBIx::Class::Storage::DBI> would normally
102 handle gets delegated to one of the two attributes: L</read_handler> or to
103 L</write_handler>. Additionally, some methods need to be distributed
104 to all existing storages. This way our storage class is a drop in replacement
105 for L<DBIx::Class::Storage::DBI>.
107 Read traffic is spread across the replicants (slaves) occuring to a user
108 selected algorithm. The default algorithm is random weighted.
112 The consistancy betweeen master and replicants is database specific. The Pool
113 gives you a method to validate its replicants, removing and replacing them
114 when they fail/pass predefined criteria. Please make careful use of the ways
115 to force a query to run against Master when needed.
119 Replicated Storage has additional requirements not currently part of L<DBIx::Class>
122 MooseX::Types => '0.16',
123 namespace::clean => '0.11',
124 Hash::Merge => '0.11'
126 You will need to install these modules manually via CPAN or make them part of the
127 Makefile for your distribution.
131 This class defines the following attributes.
135 The underlying L<DBIx::Class::Schema> object this storage is attaching
148 Contains the classname which will instantiate the L</pool> object. Defaults
149 to: L<DBIx::Class::Storage::DBI::Replicated::Pool>.
156 default=>'DBIx::Class::Storage::DBI::Replicated::Pool',
158 'create_pool' => 'new',
164 Contains a hashref of initialized information to pass to the Balancer object.
165 See L<DBIx::Class::Storage::DBI::Replicated::Pool> for available arguments.
179 The replication pool requires a balance class to provider the methods for
180 choose how to spread the query load across each replicant in the pool.
184 has 'balancer_type' => (
186 isa=>BalancerClassNamePart,
189 default=> 'DBIx::Class::Storage::DBI::Replicated::Balancer::First',
191 'create_balancer' => 'new',
197 Contains a hashref of initialized information to pass to the Balancer object.
198 See L<DBIx::Class::Storage::DBI::Replicated::Balancer> for available arguments.
202 has 'balancer_args' => (
212 Is a <DBIx::Class::Storage::DBI::Replicated::Pool> or derived class. This is a
213 container class for one or more replicated databases.
219 isa=>'DBIx::Class::Storage::DBI::Replicated::Pool',
230 Is a <DBIx::Class::Storage::DBI::Replicated::Balancer> or derived class. This
231 is a class that takes a pool (<DBIx::Class::Storage::DBI::Replicated::Pool>)
237 isa=>'DBIx::Class::Storage::DBI::Replicated::Balancer',
239 handles=>[qw/auto_validate_every/],
244 The master defines the canonical state for a pool of connected databases. All
245 the replicants are expected to match this databases state. Thus, in a classic
246 Master / Slaves distributed system, all the slaves are expected to replicate
247 the Master's state as quick as possible. This is the only database in the
248 pool of databases that is allowed to handle write traffic.
258 =head1 ATTRIBUTES IMPLEMENTING THE DBIx::Storage::DBI INTERFACE
260 The following methods are delegated all the methods required for the
261 L<DBIx::Class::Storage::DBI> interface.
265 Defines an object that implements the read side of L<BIx::Class::Storage::DBI>.
269 has 'read_handler' => (
282 Defines an object that implements the write side of L<BIx::Class::Storage::DBI>.
286 has 'write_handler' => (
298 deployment_statements
301 build_datetime_parser
315 with_deferred_fk_checks
318 with_deferred_fk_checks
332 has _master_connect_info_opts =>
333 (is => 'rw', isa => HashRef, default => sub { {} });
335 =head2 around: connect_info
337 Preserve master's C<connect_info> options (for merging with replicants.)
338 Also set any Replicated related options from connect_info, such as
339 C<pool_type>, C<pool_args>, C<balancer_type> and C<balancer_args>.
343 around connect_info => sub {
344 my ($next, $self, $info, @extra) = @_;
346 my $wantarray = wantarray;
349 for my $arg (@$info) {
350 next unless (reftype($arg)||'') eq 'HASH';
351 %opts = %{ merge($arg, \%opts) };
355 if (@opts{qw/pool_type pool_args/}) {
356 $self->pool_type(delete $opts{pool_type})
360 merge((delete $opts{pool_args} || {}), $self->pool_args)
363 $self->pool($self->_build_pool)
367 if (@opts{qw/balancer_type balancer_args/}) {
368 $self->balancer_type(delete $opts{balancer_type})
369 if $opts{balancer_type};
371 $self->balancer_args(
372 merge((delete $opts{balancer_args} || {}), $self->balancer_args)
375 $self->balancer($self->_build_balancer)
379 $self->_master_connect_info_opts(\%opts);
383 @res = $self->$next($info, @extra);
385 $res = $self->$next($info, @extra);
388 # Make sure master is blessed into the correct class and apply role to it.
389 my $master = $self->master;
390 $master->_determine_driver;
391 Moose::Meta::Class->initialize(ref $master);
392 DBIx::Class::Storage::DBI::Replicated::WithDSN->meta->apply($master);
394 $wantarray ? @res : $res;
399 This class defines the following methods.
403 L<DBIx::Class::Schema> when instantiating its storage passed itself as the
404 first argument. So we need to massage the arguments a bit so that all the
405 bits get put into the correct places.
410 my ($class, $schema, $storage_type_args, @args) = @_;
421 Lazy builder for the L</master> attribute.
427 my $master = DBIx::Class::Storage::DBI->new($self->schema);
433 Lazy builder for the L</pool> attribute.
439 $self->create_pool(%{$self->pool_args});
442 =head2 _build_balancer
444 Lazy builder for the L</balancer> attribute. This takes a Pool object so that
445 the balancer knows which pool it's balancing.
449 sub _build_balancer {
451 $self->create_balancer(
453 master=>$self->master,
454 %{$self->balancer_args},
458 =head2 _build_write_handler
460 Lazy builder for the L</write_handler> attribute. The default is to set this to
465 sub _build_write_handler {
466 return shift->master;
469 =head2 _build_read_handler
471 Lazy builder for the L</read_handler> attribute. The default is to set this to
476 sub _build_read_handler {
477 return shift->balancer;
480 =head2 around: connect_replicants
482 All calls to connect_replicants needs to have an existing $schema tacked onto
483 top of the args, since L<DBIx::Storage::DBI> needs it, and any C<connect_info>
484 options merged with the master, with replicant opts having higher priority.
488 around connect_replicants => sub {
489 my ($next, $self, @args) = @_;
492 $r = [ $r ] unless reftype $r eq 'ARRAY';
494 $self->throw_exception('coderef replicant connect_info not supported')
495 if ref $r->[0] && reftype $r->[0] eq 'CODE';
497 # any connect_info options?
499 $i++ while $i < @$r && (reftype($r->[$i])||'') ne 'HASH';
502 $r->[$i] = {} unless $r->[$i];
504 # merge if two hashes
505 my @hashes = @$r[$i .. $#{$r}];
507 $self->throw_exception('invalid connect_info options')
508 if (grep { reftype($_) eq 'HASH' } @hashes) != @hashes;
510 $self->throw_exception('too many hashrefs in connect_info')
513 my %opts = %{ merge(reverse @hashes) };
516 splice @$r, $i+1, ($#{$r} - $i), ();
518 # make sure master/replicants opts don't clash
519 my %master_opts = %{ $self->_master_connect_info_opts };
520 if (exists $opts{dbh_maker}) {
521 delete @master_opts{qw/dsn user password/};
523 delete $master_opts{dbh_maker};
526 %opts = %{ merge(\%opts, \%master_opts) };
532 $self->$next($self->schema, @args);
537 Returns an array of of all the connected storage backends. The first element
538 in the returned array is the master, and the remainings are each of the
545 return grep {defined $_ && blessed $_} (
547 values %{ $self->replicants },
551 =head2 execute_reliably ($coderef, ?@args)
553 Given a coderef, saves the current state of the L</read_handler>, forces it to
554 use reliable storage (ie sets it to the master), executes a coderef and then
555 restores the original state.
561 $schema->resultset('User')->create({name=>$name});
562 my $user_rs = $schema->resultset('User')->find({name=>$name});
566 my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
568 Use this when you must be certain of your database state, such as when you just
569 inserted something and need to get a resultset including it, etc.
573 sub execute_reliably {
574 my ($self, $coderef, @args) = @_;
576 unless( ref $coderef eq 'CODE') {
577 $self->throw_exception('Second argument must be a coderef');
580 ##Get copy of master storage
581 my $master = $self->master;
583 ##Get whatever the current read hander is
584 my $current = $self->read_handler;
586 ##Set the read handler to master
587 $self->read_handler($master);
589 ## do whatever the caller needs
591 my $want_array = wantarray;
595 @result = $coderef->(@args);
596 } elsif(defined $want_array) {
597 ($result[0]) = ($coderef->(@args));
603 ##Reset to the original state
604 $self->read_handler($current);
606 ##Exception testing has to come last, otherwise you might leave the
607 ##read_handler set to master.
610 $self->throw_exception("coderef returned an error: $@");
612 return $want_array ? @result : $result[0];
616 =head2 set_reliable_storage
618 Sets the current $schema to be 'reliable', that is all queries, both read and
619 write are sent to the master
623 sub set_reliable_storage {
625 my $schema = $self->schema;
626 my $write_handler = $self->schema->storage->write_handler;
628 $schema->storage->read_handler($write_handler);
631 =head2 set_balanced_storage
633 Sets the current $schema to be use the </balancer> for all reads, while all
634 writea are sent to the master only
638 sub set_balanced_storage {
640 my $schema = $self->schema;
641 my $balanced_handler = $self->schema->storage->balancer;
643 $schema->storage->read_handler($balanced_handler);
648 Check that the master and at least one of the replicants is connected.
655 $self->master->connected &&
656 $self->pool->connected_replicants;
659 =head2 ensure_connected
661 Make sure all the storages are connected.
665 sub ensure_connected {
667 foreach my $source ($self->all_storages) {
668 $source->ensure_connected(@_);
674 Set the limit_dialect for all existing storages
680 foreach my $source ($self->all_storages) {
681 $source->limit_dialect(@_);
683 return $self->master->quote_char;
688 Set the quote_char for all existing storages
694 foreach my $source ($self->all_storages) {
695 $source->quote_char(@_);
697 return $self->master->quote_char;
702 Set the name_sep for all existing storages
708 foreach my $source ($self->all_storages) {
709 $source->name_sep(@_);
711 return $self->master->name_sep;
716 Set the schema object for all existing storages
722 foreach my $source ($self->all_storages) {
723 $source->set_schema(@_);
729 set a debug flag across all storages
736 foreach my $source ($self->all_storages) {
740 return $self->master->debug;
745 set a debug object across all storages
752 foreach my $source ($self->all_storages) {
753 $source->debugobj(@_);
756 return $self->master->debugobj;
761 set a debugfh object across all storages
768 foreach my $source ($self->all_storages) {
769 $source->debugfh(@_);
772 return $self->master->debugfh;
777 set a debug callback across all storages
784 foreach my $source ($self->all_storages) {
785 $source->debugcb(@_);
788 return $self->master->debugcb;
793 disconnect everything
799 foreach my $source ($self->all_storages) {
800 $source->disconnect(@_);
806 set cursor class on all storages, or return master's
811 my ($self, $cursor_class) = @_;
814 $_->cursor_class($cursor_class) for $self->all_storages;
816 $self->master->cursor_class;
821 Due to the fact that replicants can lag behind a master, you must take care to
822 make sure you use one of the methods to force read queries to a master should
823 you need realtime data integrity. For example, if you insert a row, and then
824 immediately re-read it from the database (say, by doing $row->discard_changes)
825 or you insert a row and then immediately build a query that expects that row
826 to be an item, you should force the master to handle reads. Otherwise, due to
827 the lag, there is no certainty your data will be in the expected state.
829 For data integrity, all transactions automatically use the master storage for
830 all read and write queries. Using a transaction is the preferred and recommended
831 method to force the master to handle all read queries.
833 Otherwise, you can force a single query to use the master with the 'force_pool'
836 my $row = $resultset->search(undef, {force_pool=>'master'})->find($pk);
838 This attribute will safely be ignore by non replicated storages, so you can use
839 the same code for both types of systems.
841 Lastly, you can use the L</execute_reliably> method, which works very much like
844 For debugging, you can turn replication on/off with the methods L</set_reliable_storage>
845 and L</set_balanced_storage>, however this operates at a global level and is not
846 suitable if you have a shared Schema object being used by multiple processes,
847 such as on a web application server. You can get around this limitation by
848 using the Schema clone method.
850 my $new_schema = $schema->clone;
851 $new_schema->set_reliable_storage;
853 ## $new_schema will use only the Master storage for all reads/writes while
854 ## the $schema object will use replicated storage.
858 John Napiorkowski <john.napiorkowski@takkle.com>
860 Based on code originated by:
862 Norbert Csongrádi <bert@cpan.org>
863 Peter Siklósi <einon@einon.hu>
867 You may distribute this code under the same terms as Perl itself.
871 __PACKAGE__->meta->make_immutable;