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' => '0.21',
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 my $schema = Schema::Class->clone;
54 $schema->storage_type( ['::DBI::Replicated', {balancer=>'::Random'}] );
55 $schema->connection(...);
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::DBI::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.
87 See L<DBIx::Class::Storage::DBI::Replicated::Instructions> for more help and
92 Warning: This class is marked BETA. This has been running a production
93 website using MySQL native replication as its backend and we have some decent
94 test coverage but the code hasn't yet been stressed by a variety of databases.
95 Individual DB's may have quirks we are not aware of. Please use this in first
96 development and pass along your experiences/bug fixes.
98 This class implements replicated data store for DBI. Currently you can define
99 one master and numerous slave database connections. All write-type queries
100 (INSERT, UPDATE, DELETE and even LAST_INSERT_ID) are routed to master
101 database, all read-type queries (SELECTs) go to the slave database.
103 Basically, any method request that L<DBIx::Class::Storage::DBI> would normally
104 handle gets delegated to one of the two attributes: L</read_handler> or to
105 L</write_handler>. Additionally, some methods need to be distributed
106 to all existing storages. This way our storage class is a drop in replacement
107 for L<DBIx::Class::Storage::DBI>.
109 Read traffic is spread across the replicants (slaves) occuring to a user
110 selected algorithm. The default algorithm is random weighted.
114 The consistancy betweeen master and replicants is database specific. The Pool
115 gives you a method to validate its replicants, removing and replacing them
116 when they fail/pass predefined criteria. Please make careful use of the ways
117 to force a query to run against Master when needed.
121 Replicated Storage has additional requirements not currently part of L<DBIx::Class>
124 MooseX::Types => '0.21',
125 namespace::clean => '0.11',
126 Hash::Merge => '0.11'
128 You will need to install these modules manually via CPAN or make them part of the
129 Makefile for your distribution.
133 This class defines the following attributes.
137 The underlying L<DBIx::Class::Schema> object this storage is attaching
150 Contains the classname which will instantiate the L</pool> object. Defaults
151 to: L<DBIx::Class::Storage::DBI::Replicated::Pool>.
158 default=>'DBIx::Class::Storage::DBI::Replicated::Pool',
160 'create_pool' => 'new',
166 Contains a hashref of initialized information to pass to the Balancer object.
167 See L<DBIx::Class::Storage::DBI::Replicated::Pool> for available arguments.
181 The replication pool requires a balance class to provider the methods for
182 choose how to spread the query load across each replicant in the pool.
186 has 'balancer_type' => (
188 isa=>BalancerClassNamePart,
191 default=> 'DBIx::Class::Storage::DBI::Replicated::Balancer::First',
193 'create_balancer' => 'new',
199 Contains a hashref of initialized information to pass to the Balancer object.
200 See L<DBIx::Class::Storage::DBI::Replicated::Balancer> for available arguments.
204 has 'balancer_args' => (
214 Is a <DBIx::Class::Storage::DBI::Replicated::Pool> or derived class. This is a
215 container class for one or more replicated databases.
221 isa=>'DBIx::Class::Storage::DBI::Replicated::Pool',
232 Is a <DBIx::Class::Storage::DBI::Replicated::Balancer> or derived class. This
233 is a class that takes a pool (<DBIx::Class::Storage::DBI::Replicated::Pool>)
239 isa=>'DBIx::Class::Storage::DBI::Replicated::Balancer',
241 handles=>[qw/auto_validate_every/],
246 The master defines the canonical state for a pool of connected databases. All
247 the replicants are expected to match this databases state. Thus, in a classic
248 Master / Slaves distributed system, all the slaves are expected to replicate
249 the Master's state as quick as possible. This is the only database in the
250 pool of databases that is allowed to handle write traffic.
260 =head1 ATTRIBUTES IMPLEMENTING THE DBIx::Storage::DBI INTERFACE
262 The following methods are delegated all the methods required for the
263 L<DBIx::Class::Storage::DBI> interface.
267 Defines an object that implements the read side of L<BIx::Class::Storage::DBI>.
271 has 'read_handler' => (
284 Defines an object that implements the write side of L<BIx::Class::Storage::DBI>.
288 has 'write_handler' => (
300 deployment_statements
303 build_datetime_parser
317 with_deferred_fk_checks
320 with_deferred_fk_checks
331 relname_to_table_alias
332 _straight_join_to_node
336 has _master_connect_info_opts =>
337 (is => 'rw', isa => HashRef, default => sub { {} });
339 =head2 around: connect_info
341 Preserve master's C<connect_info> options (for merging with replicants.)
342 Also set any Replicated related options from connect_info, such as
343 C<pool_type>, C<pool_args>, C<balancer_type> and C<balancer_args>.
347 around connect_info => sub {
348 my ($next, $self, $info, @extra) = @_;
350 my $wantarray = wantarray;
353 for my $arg (@$info) {
354 next unless (reftype($arg)||'') eq 'HASH';
355 %opts = %{ merge($arg, \%opts) };
359 if (@opts{qw/pool_type pool_args/}) {
360 $self->pool_type(delete $opts{pool_type})
364 merge((delete $opts{pool_args} || {}), $self->pool_args)
367 $self->pool($self->_build_pool)
371 if (@opts{qw/balancer_type balancer_args/}) {
372 $self->balancer_type(delete $opts{balancer_type})
373 if $opts{balancer_type};
375 $self->balancer_args(
376 merge((delete $opts{balancer_args} || {}), $self->balancer_args)
379 $self->balancer($self->_build_balancer)
383 $self->_master_connect_info_opts(\%opts);
387 @res = $self->$next($info, @extra);
389 $res = $self->$next($info, @extra);
392 # Make sure master is blessed into the correct class and apply role to it.
393 my $master = $self->master;
394 $master->_determine_driver;
395 Moose::Meta::Class->initialize(ref $master);
397 DBIx::Class::Storage::DBI::Replicated::WithDSN->meta->apply($master);
399 # link pool back to master
400 $self->pool->master($master);
402 $wantarray ? @res : $res;
407 This class defines the following methods.
411 L<DBIx::Class::Schema> when instantiating its storage passed itself as the
412 first argument. So we need to massage the arguments a bit so that all the
413 bits get put into the correct places.
418 my ($class, $schema, $storage_type_args, @args) = @_;
429 Lazy builder for the L</master> attribute.
435 my $master = DBIx::Class::Storage::DBI->new($self->schema);
441 Lazy builder for the L</pool> attribute.
447 $self->create_pool(%{$self->pool_args});
450 =head2 _build_balancer
452 Lazy builder for the L</balancer> attribute. This takes a Pool object so that
453 the balancer knows which pool it's balancing.
457 sub _build_balancer {
459 $self->create_balancer(
461 master=>$self->master,
462 %{$self->balancer_args},
466 =head2 _build_write_handler
468 Lazy builder for the L</write_handler> attribute. The default is to set this to
473 sub _build_write_handler {
474 return shift->master;
477 =head2 _build_read_handler
479 Lazy builder for the L</read_handler> attribute. The default is to set this to
484 sub _build_read_handler {
485 return shift->balancer;
488 =head2 around: connect_replicants
490 All calls to connect_replicants needs to have an existing $schema tacked onto
491 top of the args, since L<DBIx::Storage::DBI> needs it, and any C<connect_info>
492 options merged with the master, with replicant opts having higher priority.
496 around connect_replicants => sub {
497 my ($next, $self, @args) = @_;
500 $r = [ $r ] unless reftype $r eq 'ARRAY';
502 $self->throw_exception('coderef replicant connect_info not supported')
503 if ref $r->[0] && reftype $r->[0] eq 'CODE';
505 # any connect_info options?
507 $i++ while $i < @$r && (reftype($r->[$i])||'') ne 'HASH';
510 $r->[$i] = {} unless $r->[$i];
512 # merge if two hashes
513 my @hashes = @$r[$i .. $#{$r}];
515 $self->throw_exception('invalid connect_info options')
516 if (grep { reftype($_) eq 'HASH' } @hashes) != @hashes;
518 $self->throw_exception('too many hashrefs in connect_info')
521 my %opts = %{ merge(reverse @hashes) };
524 splice @$r, $i+1, ($#{$r} - $i), ();
526 # make sure master/replicants opts don't clash
527 my %master_opts = %{ $self->_master_connect_info_opts };
528 if (exists $opts{dbh_maker}) {
529 delete @master_opts{qw/dsn user password/};
531 delete $master_opts{dbh_maker};
534 %opts = %{ merge(\%opts, \%master_opts) };
540 $self->$next($self->schema, @args);
545 Returns an array of of all the connected storage backends. The first element
546 in the returned array is the master, and the remainings are each of the
553 return grep {defined $_ && blessed $_} (
555 values %{ $self->replicants },
559 =head2 execute_reliably ($coderef, ?@args)
561 Given a coderef, saves the current state of the L</read_handler>, forces it to
562 use reliable storage (ie sets it to the master), executes a coderef and then
563 restores the original state.
569 $schema->resultset('User')->create({name=>$name});
570 my $user_rs = $schema->resultset('User')->find({name=>$name});
574 my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
576 Use this when you must be certain of your database state, such as when you just
577 inserted something and need to get a resultset including it, etc.
581 sub execute_reliably {
582 my ($self, $coderef, @args) = @_;
584 unless( ref $coderef eq 'CODE') {
585 $self->throw_exception('Second argument must be a coderef');
588 ##Get copy of master storage
589 my $master = $self->master;
591 ##Get whatever the current read hander is
592 my $current = $self->read_handler;
594 ##Set the read handler to master
595 $self->read_handler($master);
597 ## do whatever the caller needs
599 my $want_array = wantarray;
603 @result = $coderef->(@args);
604 } elsif(defined $want_array) {
605 ($result[0]) = ($coderef->(@args));
611 ##Reset to the original state
612 $self->read_handler($current);
614 ##Exception testing has to come last, otherwise you might leave the
615 ##read_handler set to master.
618 $self->throw_exception("coderef returned an error: $@");
620 return $want_array ? @result : $result[0];
624 =head2 set_reliable_storage
626 Sets the current $schema to be 'reliable', that is all queries, both read and
627 write are sent to the master
631 sub set_reliable_storage {
633 my $schema = $self->schema;
634 my $write_handler = $self->schema->storage->write_handler;
636 $schema->storage->read_handler($write_handler);
639 =head2 set_balanced_storage
641 Sets the current $schema to be use the </balancer> for all reads, while all
642 writea are sent to the master only
646 sub set_balanced_storage {
648 my $schema = $self->schema;
649 my $balanced_handler = $self->schema->storage->balancer;
651 $schema->storage->read_handler($balanced_handler);
656 Check that the master and at least one of the replicants is connected.
663 $self->master->connected &&
664 $self->pool->connected_replicants;
667 =head2 ensure_connected
669 Make sure all the storages are connected.
673 sub ensure_connected {
675 foreach my $source ($self->all_storages) {
676 $source->ensure_connected(@_);
682 Set the limit_dialect for all existing storages
688 foreach my $source ($self->all_storages) {
689 $source->limit_dialect(@_);
691 return $self->master->quote_char;
696 Set the quote_char for all existing storages
702 foreach my $source ($self->all_storages) {
703 $source->quote_char(@_);
705 return $self->master->quote_char;
710 Set the name_sep for all existing storages
716 foreach my $source ($self->all_storages) {
717 $source->name_sep(@_);
719 return $self->master->name_sep;
724 Set the schema object for all existing storages
730 foreach my $source ($self->all_storages) {
731 $source->set_schema(@_);
737 set a debug flag across all storages
744 foreach my $source ($self->all_storages) {
748 return $self->master->debug;
759 return $self->master->debugobj(@_);
770 return $self->master->debugfh(@_);
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;