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>.
144 default=>'DBIx::Class::Storage::DBI::Replicated::Pool',
146 'create_pool' => 'new',
152 Contains a hashref of initialized information to pass to the Balancer object.
153 See L<DBIx::Class::Storage::Replicated::Pool> for available arguments.
167 The replication pool requires a balance class to provider the methods for
168 choose how to spread the query load across each replicant in the pool.
172 has 'balancer_type' => (
174 isa=>BalancerClassNamePart,
177 default=> 'DBIx::Class::Storage::DBI::Replicated::Balancer::First',
179 'create_balancer' => 'new',
185 Contains a hashref of initialized information to pass to the Balancer object.
186 See L<DBIx::Class::Storage::Replicated::Balancer> for available arguments.
190 has 'balancer_args' => (
200 Is a <DBIx::Class::Storage::DBI::Replicated::Pool> or derived class. This is a
201 container class for one or more replicated databases.
207 isa=>'DBIx::Class::Storage::DBI::Replicated::Pool',
218 Is a <DBIx::Class::Storage::DBI::Replicated::Balancer> or derived class. This
219 is a class that takes a pool (<DBIx::Class::Storage::DBI::Replicated::Pool>)
225 isa=>'DBIx::Class::Storage::DBI::Replicated::Balancer',
227 handles=>[qw/auto_validate_every/],
232 The master defines the canonical state for a pool of connected databases. All
233 the replicants are expected to match this databases state. Thus, in a classic
234 Master / Slaves distributed system, all the slaves are expected to replicate
235 the Master's state as quick as possible. This is the only database in the
236 pool of databases that is allowed to handle write traffic.
242 isa=>'DBIx::Class::Storage::DBI',
246 =head1 ATTRIBUTES IMPLEMENTING THE DBIx::Storage::DBI INTERFACE
248 The following methods are delegated all the methods required for the
249 L<DBIx::Class::Storage::DBI> interface.
253 Defines an object that implements the read side of L<BIx::Class::Storage::DBI>.
257 has 'read_handler' => (
270 Defines an object that implements the write side of L<BIx::Class::Storage::DBI>.
274 has 'write_handler' => (
286 deployment_statements
302 with_deferred_fk_checks
310 has _master_connect_info_opts =>
311 (is => 'rw', isa => HashRef, default => sub { {} });
313 =head2 around: connect_info
315 Preserve master's C<connect_info> options (for merging with replicants.)
316 Also set any Replicated related options from connect_info, such as
317 C<pool_type>, C<pool_args>, C<balancer_type> and C<balancer_args>.
321 around connect_info => sub {
322 my ($next, $self, $info, @extra) = @_;
325 for my $arg (@$info) {
326 next unless (reftype($arg)||'') eq 'HASH';
327 %opts = (%opts, %$arg);
331 if (@opts{qw/pool_type pool_args/}) {
332 $self->pool_type(delete $opts{pool_type})
336 %{ $self->pool_args },
337 %{ delete $opts{pool_args} || {} }
340 $self->pool($self->_build_pool);
343 if (@opts{qw/balancer_type balancer_args/}) {
344 $self->balancer_type(delete $opts{balancer_type})
345 if $opts{balancer_type};
347 $self->balancer_args({
348 %{ $self->balancer_args },
349 %{ delete $opts{balancer_args} || {} }
352 $self->balancer($self->_build_balancer);
355 $self->_master_connect_info_opts(\%opts);
357 $self->$next($info, @extra);
362 This class defines the following methods.
366 L<DBIx::Class::Schema> when instantiating it's storage passed itself as the
367 first argument. So we need to massage the arguments a bit so that all the
368 bits get put into the correct places.
373 my ($class, $schema, $storage_type_args, @args) = @_;
384 Lazy builder for the L</master> attribute.
390 my $master = DBIx::Class::Storage::DBI->new($self->schema);
391 DBIx::Class::Storage::DBI::Replicated::WithDSN->meta->apply($master);
397 Lazy builder for the L</pool> attribute.
403 $self->create_pool(%{$self->pool_args});
406 =head2 _build_balancer
408 Lazy builder for the L</balancer> attribute. This takes a Pool object so that
409 the balancer knows which pool it's balancing.
413 sub _build_balancer {
415 $self->create_balancer(
417 master=>$self->master,
418 %{$self->balancer_args},
422 =head2 _build_write_handler
424 Lazy builder for the L</write_handler> attribute. The default is to set this to
429 sub _build_write_handler {
430 return shift->master;
433 =head2 _build_read_handler
435 Lazy builder for the L</read_handler> attribute. The default is to set this to
440 sub _build_read_handler {
441 return shift->balancer;
444 =head2 around: connect_replicants
446 All calls to connect_replicants needs to have an existing $schema tacked onto
447 top of the args, since L<DBIx::Storage::DBI> needs it, and any C<connect_info>
448 options merged with the master, with replicant opts having higher priority.
452 around connect_replicants => sub {
453 my ($next, $self, @args) = @_;
456 $r = [ $r ] unless reftype $r eq 'ARRAY';
458 croak "coderef replicant connect_info not supported"
459 if ref $r->[0] && reftype $r->[0] eq 'CODE';
461 # any connect_info options?
463 $i++ while $i < @$r && (reftype($r->[$i])||'') ne 'HASH';
466 $r->[$i] = {} unless $r->[$i];
468 # merge if two hashes
469 my %opts = map %$_, @$r[$i .. $#{$r}];
470 splice @$r, $i+1, ($#{$r} - $i), ();
473 %opts = (%{ $self->_master_connect_info_opts }, %opts);
479 $self->$next($self->schema, @args);
484 Returns an array of of all the connected storage backends. The first element
485 in the returned array is the master, and the remainings are each of the
492 return grep {defined $_ && blessed $_} (
494 values %{ $self->replicants },
498 =head2 execute_reliably ($coderef, ?@args)
500 Given a coderef, saves the current state of the L</read_handler>, forces it to
501 use reliable storage (ie sets it to the master), executes a coderef and then
502 restores the original state.
508 $schema->resultset('User')->create({name=>$name});
509 my $user_rs = $schema->resultset('User')->find({name=>$name});
513 my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
515 Use this when you must be certain of your database state, such as when you just
516 inserted something and need to get a resultset including it, etc.
520 sub execute_reliably {
521 my ($self, $coderef, @args) = @_;
523 unless( ref $coderef eq 'CODE') {
524 $self->throw_exception('Second argument must be a coderef');
527 ##Get copy of master storage
528 my $master = $self->master;
530 ##Get whatever the current read hander is
531 my $current = $self->read_handler;
533 ##Set the read handler to master
534 $self->read_handler($master);
536 ## do whatever the caller needs
538 my $want_array = wantarray;
542 @result = $coderef->(@args);
543 } elsif(defined $want_array) {
544 ($result[0]) = ($coderef->(@args));
550 ##Reset to the original state
551 $self->read_handler($current);
553 ##Exception testing has to come last, otherwise you might leave the
554 ##read_handler set to master.
557 $self->throw_exception("coderef returned an error: $@");
559 return $want_array ? @result : $result[0];
563 =head2 set_reliable_storage
565 Sets the current $schema to be 'reliable', that is all queries, both read and
566 write are sent to the master
570 sub set_reliable_storage {
572 my $schema = $self->schema;
573 my $write_handler = $self->schema->storage->write_handler;
575 $schema->storage->read_handler($write_handler);
578 =head2 set_balanced_storage
580 Sets the current $schema to be use the </balancer> for all reads, while all
581 writea are sent to the master only
585 sub set_balanced_storage {
587 my $schema = $self->schema;
588 my $write_handler = $self->schema->storage->balancer;
590 $schema->storage->read_handler($write_handler);
593 =head2 around: txn_do ($coderef)
595 Overload to the txn_do method, which is delegated to whatever the
596 L<write_handler> is set to. We overload this in order to wrap in inside a
597 L</execute_reliably> method.
601 around 'txn_do' => sub {
602 my($txn_do, $self, $coderef, @args) = @_;
603 $self->execute_reliably(sub {$self->$txn_do($coderef, @args)});
608 Check that the master and at least one of the replicants is connected.
615 $self->master->connected &&
616 $self->pool->connected_replicants;
619 =head2 ensure_connected
621 Make sure all the storages are connected.
625 sub ensure_connected {
627 foreach my $source ($self->all_storages) {
628 $source->ensure_connected(@_);
634 Set the limit_dialect for all existing storages
640 foreach my $source ($self->all_storages) {
641 $source->limit_dialect(@_);
643 return $self->master->quote_char;
648 Set the quote_char for all existing storages
654 foreach my $source ($self->all_storages) {
655 $source->quote_char(@_);
657 return $self->master->quote_char;
662 Set the name_sep for all existing storages
668 foreach my $source ($self->all_storages) {
669 $source->name_sep(@_);
671 return $self->master->name_sep;
676 Set the schema object for all existing storages
682 foreach my $source ($self->all_storages) {
683 $source->set_schema(@_);
689 set a debug flag across all storages
696 foreach my $source ($self->all_storages) {
700 return $self->master->debug;
705 set a debug object across all storages
712 foreach my $source ($self->all_storages) {
713 $source->debugobj(@_);
716 return $self->master->debugobj;
721 set a debugfh object across all storages
728 foreach my $source ($self->all_storages) {
729 $source->debugfh(@_);
732 return $self->master->debugfh;
737 set a debug callback across all storages
744 foreach my $source ($self->all_storages) {
745 $source->debugcb(@_);
748 return $self->master->debugcb;
753 disconnect everything
759 foreach my $source ($self->all_storages) {
760 $source->disconnect(@_);
766 set cursor class on all storages, or return master's
771 my ($self, $cursor_class) = @_;
774 $_->cursor_class($cursor_class) for $self->all_storages;
776 $self->master->cursor_class;
781 Due to the fact that replicants can lag behind a master, you must take care to
782 make sure you use one of the methods to force read queries to a master should
783 you need realtime data integrity. For example, if you insert a row, and then
784 immediately re-read it from the database (say, by doing $row->discard_changes)
785 or you insert a row and then immediately build a query that expects that row
786 to be an item, you should force the master to handle reads. Otherwise, due to
787 the lag, there is no certainty your data will be in the expected state.
789 For data integrity, all transactions automatically use the master storage for
790 all read and write queries. Using a transaction is the preferred and recommended
791 method to force the master to handle all read queries.
793 Otherwise, you can force a single query to use the master with the 'force_pool'
796 my $row = $resultset->search(undef, {force_pool=>'master'})->find($pk);
798 This attribute will safely be ignore by non replicated storages, so you can use
799 the same code for both types of systems.
801 Lastly, you can use the L</execute_reliably> method, which works very much like
804 For debugging, you can turn replication on/off with the methods L</set_reliable_storage>
805 and L</set_balanced_storage>, however this operates at a global level and is not
806 suitable if you have a shared Schema object being used by multiple processes,
807 such as on a web application server. You can get around this limitation by
808 using the Schema clone method.
810 my $new_schema = $schema->clone;
811 $new_schema->set_reliable_storage;
813 ## $new_schema will use only the Master storage for all reads/writes while
814 ## the $schema object will use replicated storage.
818 John Napiorkowski <john.napiorkowski@takkle.com>
820 Based on code originated by:
822 Norbert Csongrádi <bert@cpan.org>
823 Peter Siklósi <einon@einon.hu>
827 You may distribute this code under the same terms as Perl itself.
831 __PACKAGE__->meta->make_immutable;