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',
14 'Hash::Merge' => '0.11'
19 for my $module (keys %replication_required) {
20 eval "use $module $replication_required{$module}";
21 push @didnt_load, "$module $replication_required{$module}"
25 croak("@{[ join ', ', @didnt_load ]} are missing and are required for Replication")
30 use DBIx::Class::Storage::DBI;
31 use DBIx::Class::Storage::DBI::Replicated::Pool;
32 use DBIx::Class::Storage::DBI::Replicated::Balancer;
33 use DBIx::Class::Storage::DBI::Replicated::Types 'BalancerClassNamePart';
34 use MooseX::Types::Moose qw/ClassName HashRef Object/;
35 use Scalar::Util 'reftype';
36 use Carp::Clan qw/^DBIx::Class/;
37 use Hash::Merge 'merge';
39 use namespace::clean -except => 'meta';
43 DBIx::Class::Storage::DBI::Replicated - BETA Replicated database support
47 The Following example shows how to change an existing $schema to a replicated
48 storage type, add some replicated (readonly) databases, and perform reporting
51 You should set the 'storage_type attribute to a replicated type. You should
52 also defined you arguments, such as which balancer you want and any arguments
53 that the Pool object should get.
55 $schema->storage_type( ['::DBI::Replicated', {balancer=>'::Random'}] );
57 Next, you need to add in the Replicants. Basically this is an array of
58 arrayrefs, where each arrayref is database connect information. Think of these
59 arguments as what you'd pass to the 'normal' $schema->connect method.
61 $schema->storage->connect_replicants(
62 [$dsn1, $user, $pass, \%opts],
63 [$dsn2, $user, $pass, \%opts],
64 [$dsn3, $user, $pass, \%opts],
67 Now, just use the $schema as you normally would. Automatically all reads will
68 be delegated to the replicants, while writes to the master.
70 $schema->resultset('Source')->search({name=>'etc'});
72 You can force a given query to use a particular storage using the search
73 attribute 'force_pool'. For example:
75 my $RS = $schema->resultset('Source')->search(undef, {force_pool=>'master'});
77 Now $RS will force everything (both reads and writes) to use whatever was setup
78 as the master storage. 'master' is hardcoded to always point to the Master,
79 but you can also use any Replicant name. Please see:
80 L<DBIx::Class::Storage::Replicated::Pool> and the replicants attribute for more.
82 Also see transactions and L</execute_reliably> for alternative ways to
83 force read traffic to the master. In general, you should wrap your statements
84 in a transaction when you are reading and writing to the same tables at the
85 same time, since your replicants will often lag a bit behind the master.
89 Warning: This class is marked BETA. This has been running a production
90 website using MySQL native replication as its backend and we have some decent
91 test coverage but the code hasn't yet been stressed by a variety of databases.
92 Individual DB's may have quirks we are not aware of. Please use this in first
93 development and pass along your experiences/bug fixes.
95 This class implements replicated data store for DBI. Currently you can define
96 one master and numerous slave database connections. All write-type queries
97 (INSERT, UPDATE, DELETE and even LAST_INSERT_ID) are routed to master
98 database, all read-type queries (SELECTs) go to the slave database.
100 Basically, any method request that L<DBIx::Class::Storage::DBI> would normally
101 handle gets delegated to one of the two attributes: L</read_handler> or to
102 L</write_handler>. Additionally, some methods need to be distributed
103 to all existing storages. This way our storage class is a drop in replacement
104 for L<DBIx::Class::Storage::DBI>.
106 Read traffic is spread across the replicants (slaves) occuring to a user
107 selected algorithm. The default algorithm is random weighted.
111 The consistancy betweeen master and replicants is database specific. The Pool
112 gives you a method to validate it's replicants, removing and replacing them
113 when they fail/pass predefined criteria. Please make careful use of the ways
114 to force a query to run against Master when needed.
118 Replicated Storage has additional requirements not currently part of L<DBIx::Class>
121 MooseX::AttributeHelpers => 0.12
122 MooseX::Types => 0.10
123 namespace::clean => 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
141 isa=>'DBIx::Class::Schema',
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::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::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.
254 isa=>'DBIx::Class::Storage::DBI',
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 : $res;
399 This class defines the following methods.
403 L<DBIx::Class::Schema> when instantiating it's storage passed itself as the
404 first argument. So we need to massage the arguments a bit so that all the
405 bits get put into the correct places.
410 my ($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 croak "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 croak "invalid connect_info options"
508 if (grep { reftype($_) eq 'HASH' } @hashes) != @hashes;
510 croak "too many hashrefs in connect_info"
513 my %opts = %{ merge(reverse @hashes) };
516 splice @$r, $i+1, ($#{$r} - $i), ();
519 %opts = %{ merge(\%opts, $self->_master_connect_info_opts) };
525 $self->$next($self->schema, @args);
530 Returns an array of of all the connected storage backends. The first element
531 in the returned array is the master, and the remainings are each of the
538 return grep {defined $_ && blessed $_} (
540 values %{ $self->replicants },
544 =head2 execute_reliably ($coderef, ?@args)
546 Given a coderef, saves the current state of the L</read_handler>, forces it to
547 use reliable storage (ie sets it to the master), executes a coderef and then
548 restores the original state.
554 $schema->resultset('User')->create({name=>$name});
555 my $user_rs = $schema->resultset('User')->find({name=>$name});
559 my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
561 Use this when you must be certain of your database state, such as when you just
562 inserted something and need to get a resultset including it, etc.
566 sub execute_reliably {
567 my ($self, $coderef, @args) = @_;
569 unless( ref $coderef eq 'CODE') {
570 $self->throw_exception('Second argument must be a coderef');
573 ##Get copy of master storage
574 my $master = $self->master;
576 ##Get whatever the current read hander is
577 my $current = $self->read_handler;
579 ##Set the read handler to master
580 $self->read_handler($master);
582 ## do whatever the caller needs
584 my $want_array = wantarray;
588 @result = $coderef->(@args);
589 } elsif(defined $want_array) {
590 ($result[0]) = ($coderef->(@args));
596 ##Reset to the original state
597 $self->read_handler($current);
599 ##Exception testing has to come last, otherwise you might leave the
600 ##read_handler set to master.
603 $self->throw_exception("coderef returned an error: $@");
605 return $want_array ? @result : $result[0];
609 =head2 set_reliable_storage
611 Sets the current $schema to be 'reliable', that is all queries, both read and
612 write are sent to the master
616 sub set_reliable_storage {
618 my $schema = $self->schema;
619 my $write_handler = $self->schema->storage->write_handler;
621 $schema->storage->read_handler($write_handler);
624 =head2 set_balanced_storage
626 Sets the current $schema to be use the </balancer> for all reads, while all
627 writea are sent to the master only
631 sub set_balanced_storage {
633 my $schema = $self->schema;
634 my $balanced_handler = $self->schema->storage->balancer;
636 $schema->storage->read_handler($balanced_handler);
641 Check that the master and at least one of the replicants is connected.
648 $self->master->connected &&
649 $self->pool->connected_replicants;
652 =head2 ensure_connected
654 Make sure all the storages are connected.
658 sub ensure_connected {
660 foreach my $source ($self->all_storages) {
661 $source->ensure_connected(@_);
667 Set the limit_dialect for all existing storages
673 foreach my $source ($self->all_storages) {
674 $source->limit_dialect(@_);
676 return $self->master->quote_char;
681 Set the quote_char for all existing storages
687 foreach my $source ($self->all_storages) {
688 $source->quote_char(@_);
690 return $self->master->quote_char;
695 Set the name_sep for all existing storages
701 foreach my $source ($self->all_storages) {
702 $source->name_sep(@_);
704 return $self->master->name_sep;
709 Set the schema object for all existing storages
715 foreach my $source ($self->all_storages) {
716 $source->set_schema(@_);
722 set a debug flag across all storages
729 foreach my $source ($self->all_storages) {
733 return $self->master->debug;
738 set a debug object across all storages
745 foreach my $source ($self->all_storages) {
746 $source->debugobj(@_);
749 return $self->master->debugobj;
754 set a debugfh object across all storages
761 foreach my $source ($self->all_storages) {
762 $source->debugfh(@_);
765 return $self->master->debugfh;
770 set a debug callback across all storages
777 foreach my $source ($self->all_storages) {
778 $source->debugcb(@_);
781 return $self->master->debugcb;
786 disconnect everything
792 foreach my $source ($self->all_storages) {
793 $source->disconnect(@_);
799 set cursor class on all storages, or return master's
804 my ($self, $cursor_class) = @_;
807 $_->cursor_class($cursor_class) for $self->all_storages;
809 $self->master->cursor_class;
814 Due to the fact that replicants can lag behind a master, you must take care to
815 make sure you use one of the methods to force read queries to a master should
816 you need realtime data integrity. For example, if you insert a row, and then
817 immediately re-read it from the database (say, by doing $row->discard_changes)
818 or you insert a row and then immediately build a query that expects that row
819 to be an item, you should force the master to handle reads. Otherwise, due to
820 the lag, there is no certainty your data will be in the expected state.
822 For data integrity, all transactions automatically use the master storage for
823 all read and write queries. Using a transaction is the preferred and recommended
824 method to force the master to handle all read queries.
826 Otherwise, you can force a single query to use the master with the 'force_pool'
829 my $row = $resultset->search(undef, {force_pool=>'master'})->find($pk);
831 This attribute will safely be ignore by non replicated storages, so you can use
832 the same code for both types of systems.
834 Lastly, you can use the L</execute_reliably> method, which works very much like
837 For debugging, you can turn replication on/off with the methods L</set_reliable_storage>
838 and L</set_balanced_storage>, however this operates at a global level and is not
839 suitable if you have a shared Schema object being used by multiple processes,
840 such as on a web application server. You can get around this limitation by
841 using the Schema clone method.
843 my $new_schema = $schema->clone;
844 $new_schema->set_reliable_storage;
846 ## $new_schema will use only the Master storage for all reads/writes while
847 ## the $schema object will use replicated storage.
851 John Napiorkowski <john.napiorkowski@takkle.com>
853 Based on code originated by:
855 Norbert Csongrádi <bert@cpan.org>
856 Peter Siklósi <einon@einon.hu>
860 You may distribute this code under the same terms as Perl itself.
864 __PACKAGE__->meta->make_immutable;