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")
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 'BalancerClassNamePart';
33 use MooseX::Types::Moose qw/ClassName HashRef Object/;
34 use Scalar::Util 'reftype';
35 use Carp::Clan qw/^DBIx::Class/;
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 ## Change storage_type in your schema class
50 $schema->storage_type( ['::DBI::Replicated', {balancer=>'::Random'}] );
52 ## Add some slaves. Basically this is an array of arrayrefs, where each
53 ## arrayref is database connect information
55 $schema->storage->connect_replicants(
56 [$dsn1, $user, $pass, \%opts],
57 [$dsn2, $user, $pass, \%opts],
58 [$dsn3, $user, $pass, \%opts],
61 ## Now, just use the $schema as normal
62 $schema->resultset('Source')->search({name=>'etc'});
64 ## You can force a given query to use a particular storage using the search
65 ### attribute 'force_pool'. For example:
67 my $RS = $schema->resultset('Source')->search(undef, {force_pool=>'master'});
69 ## Now $RS will force everything (both reads and writes) to use whatever was
70 ## setup as the master storage. 'master' is hardcoded to always point to the
71 ## Master, but you can also use any Replicant name. Please see:
72 ## L<DBIx::Class::Storage::Replicated::Pool> and the replicants attribute for
73 ## More. Also see transactions and L</execute_reliably> for alternative ways
74 ## to force read traffic to the master.
78 Warning: This class is marked BETA. This has been running a production
79 website using MySQL native replication as its backend and we have some decent
80 test coverage but the code hasn't yet been stressed by a variety of databases.
81 Individual DB's may have quirks we are not aware of. Please use this in first
82 development and pass along your experiences/bug fixes.
84 This class implements replicated data store for DBI. Currently you can define
85 one master and numerous slave database connections. All write-type queries
86 (INSERT, UPDATE, DELETE and even LAST_INSERT_ID) are routed to master
87 database, all read-type queries (SELECTs) go to the slave database.
89 Basically, any method request that L<DBIx::Class::Storage::DBI> would normally
90 handle gets delegated to one of the two attributes: L</read_handler> or to
91 L</write_handler>. Additionally, some methods need to be distributed
92 to all existing storages. This way our storage class is a drop in replacement
93 for L<DBIx::Class::Storage::DBI>.
95 Read traffic is spread across the replicants (slaves) occuring to a user
96 selected algorithm. The default algorithm is random weighted.
100 The consistancy betweeen master and replicants is database specific. The Pool
101 gives you a method to validate it's replicants, removing and replacing them
102 when they fail/pass predefined criteria. Please make careful use of the ways
103 to force a query to run against Master when needed.
107 Replicated Storage has additional requirements not currently part of L<DBIx::Class>
110 MooseX::AttributeHelpers => 0.12
111 MooseX::Types => 0.10
112 namespace::clean => 0.11
114 You will need to install these modules manually via CPAN or make them part of the
115 Makefile for your distribution.
119 This class defines the following attributes.
123 The underlying L<DBIx::Class::Schema> object this storage is attaching
129 isa=>'DBIx::Class::Schema',
136 Contains the classname which will instantiate the L</pool> object. Defaults
137 to: L<DBIx::Class::Storage::DBI::Replicated::Pool>.
145 default=>'DBIx::Class::Storage::DBI::Replicated::Pool',
147 'create_pool' => 'new',
153 Contains a hashref of initialized information to pass to the Balancer object.
154 See L<DBIx::Class::Storage::Replicated::Pool> for available arguments.
169 The replication pool requires a balance class to provider the methods for
170 choose how to spread the query load across each replicant in the pool.
174 has 'balancer_type' => (
176 isa=>BalancerClassNamePart,
179 default=> 'DBIx::Class::Storage::DBI::Replicated::Balancer::First',
181 'create_balancer' => 'new',
187 Contains a hashref of initialized information to pass to the Balancer object.
188 See L<DBIx::Class::Storage::Replicated::Balancer> for available arguments.
192 has 'balancer_args' => (
202 Is a <DBIx::Class::Storage::DBI::Replicated::Pool> or derived class. This is a
203 container class for one or more replicated databases.
209 isa=>'DBIx::Class::Storage::DBI::Replicated::Pool',
220 Is a <DBIx::Class::Storage::DBI::Replicated::Balancer> or derived class. This
221 is a class that takes a pool (<DBIx::Class::Storage::DBI::Replicated::Pool>)
227 isa=>'DBIx::Class::Storage::DBI::Replicated::Balancer',
229 handles=>[qw/auto_validate_every/],
234 The master defines the canonical state for a pool of connected databases. All
235 the replicants are expected to match this databases state. Thus, in a classic
236 Master / Slaves distributed system, all the slaves are expected to replicate
237 the Master's state as quick as possible. This is the only database in the
238 pool of databases that is allowed to handle write traffic.
244 isa=>'DBIx::Class::Storage::DBI',
248 =head1 ATTRIBUTES IMPLEMENTING THE DBIx::Storage::DBI INTERFACE
250 The following methods are delegated all the methods required for the
251 L<DBIx::Class::Storage::DBI> interface.
255 Defines an object that implements the read side of L<BIx::Class::Storage::DBI>.
259 has 'read_handler' => (
272 Defines an object that implements the write side of L<BIx::Class::Storage::DBI>.
276 has 'write_handler' => (
289 deployment_statements
305 with_deferred_fk_checks
313 has _master_connect_info_opts =>
314 (is => 'rw', isa => HashRef, default => sub { {} });
316 =head2 around: connect_info
318 Preserve master's C<connect_info> options (for merging with replicants.)
322 around connect_info => sub {
323 my ($next, $self, $info, @extra) = @_;
326 for my $arg (@$info) {
327 next unless (reftype($arg)||'') eq 'HASH';
328 %opts = (%opts, %$arg);
333 $self->_master_connect_info_opts(\%opts);
335 $self->$next($info, @extra);
340 This class defines the following methods.
344 L<DBIx::Class::Schema> when instantiating it's storage passed itself as the
345 first argument. So we need to massage the arguments a bit so that all the
346 bits get put into the correct places.
351 my ($class, $schema, $storage_type_args, @args) = @_;
362 Lazy builder for the L</master> attribute.
368 DBIx::Class::Storage::DBI->new($self->schema);
373 Lazy builder for the L</pool> attribute.
379 $self->create_pool(%{$self->pool_args});
382 =head2 _build_balancer
384 Lazy builder for the L</balancer> attribute. This takes a Pool object so that
385 the balancer knows which pool it's balancing.
389 sub _build_balancer {
391 $self->create_balancer(
393 master=>$self->master,
394 %{$self->balancer_args},
398 =head2 _build_write_handler
400 Lazy builder for the L</write_handler> attribute. The default is to set this to
405 sub _build_write_handler {
406 return shift->master;
409 =head2 _build_read_handler
411 Lazy builder for the L</read_handler> attribute. The default is to set this to
416 sub _build_read_handler {
417 return shift->balancer;
420 =head2 around: connect_replicants
422 All calls to connect_replicants needs to have an existing $schema tacked onto
423 top of the args, since L<DBIx::Storage::DBI> needs it, and any C<connect_info>
424 options merged with the master, with replicant opts having higher priority.
428 around connect_replicants => sub {
429 my ($next, $self, @args) = @_;
432 $r = [ $r ] unless reftype $r eq 'ARRAY';
434 croak "coderef replicant connect_info not supported"
435 if ref $r->[0] && reftype $r->[0] eq 'CODE';
437 # any connect_info options?
439 $i++ while $i < @$r && (reftype($r->[$i])||'') ne 'HASH';
442 $r->[$i] = {} unless $r->[$i];
444 # merge if two hashes
445 my %opts = map %$_, @$r[$i .. $#{$r}];
446 splice @$r, $i+1, ($#{$r} - $i), ();
449 %opts = (%{ $self->_master_connect_info_opts }, %opts);
455 $self->$next($self->schema, @args);
460 Returns an array of of all the connected storage backends. The first element
461 in the returned array is the master, and the remainings are each of the
468 return grep {defined $_ && blessed $_} (
470 values %{ $self->replicants },
474 =head2 execute_reliably ($coderef, ?@args)
476 Given a coderef, saves the current state of the L</read_handler>, forces it to
477 use reliable storage (ie sets it to the master), executes a coderef and then
478 restores the original state.
484 $schema->resultset('User')->create({name=>$name});
485 my $user_rs = $schema->resultset('User')->find({name=>$name});
489 my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
491 Use this when you must be certain of your database state, such as when you just
492 inserted something and need to get a resultset including it, etc.
496 sub execute_reliably {
497 my ($self, $coderef, @args) = @_;
499 unless( ref $coderef eq 'CODE') {
500 $self->throw_exception('Second argument must be a coderef');
503 ##Get copy of master storage
504 my $master = $self->master;
506 ##Get whatever the current read hander is
507 my $current = $self->read_handler;
509 ##Set the read handler to master
510 $self->read_handler($master);
512 ## do whatever the caller needs
514 my $want_array = wantarray;
518 @result = $coderef->(@args);
519 } elsif(defined $want_array) {
520 ($result[0]) = ($coderef->(@args));
526 ##Reset to the original state
527 $self->read_handler($current);
529 ##Exception testing has to come last, otherwise you might leave the
530 ##read_handler set to master.
533 $self->throw_exception("coderef returned an error: $@");
535 return $want_array ? @result : $result[0];
539 =head2 set_reliable_storage
541 Sets the current $schema to be 'reliable', that is all queries, both read and
542 write are sent to the master
546 sub set_reliable_storage {
548 my $schema = $self->schema;
549 my $write_handler = $self->schema->storage->write_handler;
551 $schema->storage->read_handler($write_handler);
554 =head2 set_balanced_storage
556 Sets the current $schema to be use the </balancer> for all reads, while all
557 writea are sent to the master only
561 sub set_balanced_storage {
563 my $schema = $self->schema;
564 my $write_handler = $self->schema->storage->balancer;
566 $schema->storage->read_handler($write_handler);
569 =head2 around: txn_do ($coderef)
571 Overload to the txn_do method, which is delegated to whatever the
572 L<write_handler> is set to. We overload this in order to wrap in inside a
573 L</execute_reliably> method.
577 around 'txn_do' => sub {
578 my($txn_do, $self, $coderef, @args) = @_;
579 $self->execute_reliably(sub {$self->$txn_do($coderef, @args)});
584 Check that the master and at least one of the replicants is connected.
591 $self->master->connected &&
592 $self->pool->connected_replicants;
595 =head2 ensure_connected
597 Make sure all the storages are connected.
601 sub ensure_connected {
603 foreach my $source ($self->all_storages) {
604 $source->ensure_connected(@_);
610 Set the limit_dialect for all existing storages
616 foreach my $source ($self->all_storages) {
617 $source->limit_dialect(@_);
619 return $self->master->quote_char;
624 Set the quote_char for all existing storages
630 foreach my $source ($self->all_storages) {
631 $source->quote_char(@_);
633 return $self->master->quote_char;
638 Set the name_sep for all existing storages
644 foreach my $source ($self->all_storages) {
645 $source->name_sep(@_);
647 return $self->master->name_sep;
652 Set the schema object for all existing storages
658 foreach my $source ($self->all_storages) {
659 $source->set_schema(@_);
665 set a debug flag across all storages
672 foreach my $source ($self->all_storages) {
676 return $self->master->debug;
681 set a debug object across all storages
688 foreach my $source ($self->all_storages) {
689 $source->debugobj(@_);
692 return $self->master->debugobj;
697 set a debugfh object across all storages
704 foreach my $source ($self->all_storages) {
705 $source->debugfh(@_);
708 return $self->master->debugfh;
713 set a debug callback across all storages
720 foreach my $source ($self->all_storages) {
721 $source->debugcb(@_);
724 return $self->master->debugcb;
729 disconnect everything
735 foreach my $source ($self->all_storages) {
736 $source->disconnect(@_);
742 set cursor class on all storages, or return master's
747 my ($self, $cursor_class) = @_;
750 $_->cursor_class($cursor_class) for $self->all_storages;
752 $self->master->cursor_class;
757 Due to the fact that replicants can lag behind a master, you must take care to
758 make sure you use one of the methods to force read queries to a master should
759 you need realtime data integrity. For example, if you insert a row, and then
760 immediately re-read it from the database (say, by doing $row->discard_changes)
761 or you insert a row and then immediately build a query that expects that row
762 to be an item, you should force the master to handle reads. Otherwise, due to
763 the lag, there is no certainty your data will be in the expected state.
765 For data integrity, all transactions automatically use the master storage for
766 all read and write queries. Using a transaction is the preferred and recommended
767 method to force the master to handle all read queries.
769 Otherwise, you can force a single query to use the master with the 'force_pool'
772 my $row = $resultset->search(undef, {force_pool=>'master'})->find($pk);
774 This attribute will safely be ignore by non replicated storages, so you can use
775 the same code for both types of systems.
777 Lastly, you can use the L</execute_reliably> method, which works very much like
780 For debugging, you can turn replication on/off with the methods L</set_reliable_storage>
781 and L</set_balanced_storage>, however this operates at a global level and is not
782 suitable if you have a shared Schema object being used by multiple processes,
783 such as on a web application server. You can get around this limitation by
784 using the Schema clone method.
786 my $new_schema = $schema->clone;
787 $new_schema->set_reliable_storage;
789 ## $new_schema will use only the Master storage for all reads/writes while
790 ## the $schema object will use replicated storage.
794 John Napiorkowski <john.napiorkowski@takkle.com>
796 Based on code originated by:
798 Norbert Csongrádi <bert@cpan.org>
799 Peter Siklósi <einon@einon.hu>
803 You may distribute this code under the same terms as Perl itself.
807 __PACKAGE__->meta->make_immutable;