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)
344 if (@opts{qw/balancer_type balancer_args/}) {
345 $self->balancer_type(delete $opts{balancer_type})
346 if $opts{balancer_type};
348 $self->balancer_args({
349 %{ $self->balancer_args },
350 %{ delete $opts{balancer_args} || {} }
353 $self->balancer($self->_build_balancer)
357 $self->_master_connect_info_opts(\%opts);
359 $self->$next($info, @extra);
364 This class defines the following methods.
368 L<DBIx::Class::Schema> when instantiating it's storage passed itself as the
369 first argument. So we need to massage the arguments a bit so that all the
370 bits get put into the correct places.
375 my ($class, $schema, $storage_type_args, @args) = @_;
386 Lazy builder for the L</master> attribute.
392 my $master = DBIx::Class::Storage::DBI->new($self->schema);
393 DBIx::Class::Storage::DBI::Replicated::WithDSN->meta->apply($master);
399 Lazy builder for the L</pool> attribute.
405 $self->create_pool(%{$self->pool_args});
408 =head2 _build_balancer
410 Lazy builder for the L</balancer> attribute. This takes a Pool object so that
411 the balancer knows which pool it's balancing.
415 sub _build_balancer {
417 $self->create_balancer(
419 master=>$self->master,
420 %{$self->balancer_args},
424 =head2 _build_write_handler
426 Lazy builder for the L</write_handler> attribute. The default is to set this to
431 sub _build_write_handler {
432 return shift->master;
435 =head2 _build_read_handler
437 Lazy builder for the L</read_handler> attribute. The default is to set this to
442 sub _build_read_handler {
443 return shift->balancer;
446 =head2 around: connect_replicants
448 All calls to connect_replicants needs to have an existing $schema tacked onto
449 top of the args, since L<DBIx::Storage::DBI> needs it, and any C<connect_info>
450 options merged with the master, with replicant opts having higher priority.
454 around connect_replicants => sub {
455 my ($next, $self, @args) = @_;
458 $r = [ $r ] unless reftype $r eq 'ARRAY';
460 croak "coderef replicant connect_info not supported"
461 if ref $r->[0] && reftype $r->[0] eq 'CODE';
463 # any connect_info options?
465 $i++ while $i < @$r && (reftype($r->[$i])||'') ne 'HASH';
468 $r->[$i] = {} unless $r->[$i];
470 # merge if two hashes
471 my %opts = map %$_, @$r[$i .. $#{$r}];
472 splice @$r, $i+1, ($#{$r} - $i), ();
475 %opts = (%{ $self->_master_connect_info_opts }, %opts);
481 $self->$next($self->schema, @args);
486 Returns an array of of all the connected storage backends. The first element
487 in the returned array is the master, and the remainings are each of the
494 return grep {defined $_ && blessed $_} (
496 values %{ $self->replicants },
500 =head2 execute_reliably ($coderef, ?@args)
502 Given a coderef, saves the current state of the L</read_handler>, forces it to
503 use reliable storage (ie sets it to the master), executes a coderef and then
504 restores the original state.
510 $schema->resultset('User')->create({name=>$name});
511 my $user_rs = $schema->resultset('User')->find({name=>$name});
515 my $user_rs = $schema->storage->execute_reliably($reliably, 'John');
517 Use this when you must be certain of your database state, such as when you just
518 inserted something and need to get a resultset including it, etc.
522 sub execute_reliably {
523 my ($self, $coderef, @args) = @_;
525 unless( ref $coderef eq 'CODE') {
526 $self->throw_exception('Second argument must be a coderef');
529 ##Get copy of master storage
530 my $master = $self->master;
532 ##Get whatever the current read hander is
533 my $current = $self->read_handler;
535 ##Set the read handler to master
536 $self->read_handler($master);
538 ## do whatever the caller needs
540 my $want_array = wantarray;
544 @result = $coderef->(@args);
545 } elsif(defined $want_array) {
546 ($result[0]) = ($coderef->(@args));
552 ##Reset to the original state
553 $self->read_handler($current);
555 ##Exception testing has to come last, otherwise you might leave the
556 ##read_handler set to master.
559 $self->throw_exception("coderef returned an error: $@");
561 return $want_array ? @result : $result[0];
565 =head2 set_reliable_storage
567 Sets the current $schema to be 'reliable', that is all queries, both read and
568 write are sent to the master
572 sub set_reliable_storage {
574 my $schema = $self->schema;
575 my $write_handler = $self->schema->storage->write_handler;
577 $schema->storage->read_handler($write_handler);
580 =head2 set_balanced_storage
582 Sets the current $schema to be use the </balancer> for all reads, while all
583 writea are sent to the master only
587 sub set_balanced_storage {
589 my $schema = $self->schema;
590 my $write_handler = $self->schema->storage->balancer;
592 $schema->storage->read_handler($write_handler);
595 =head2 around: txn_do ($coderef)
597 Overload to the txn_do method, which is delegated to whatever the
598 L<write_handler> is set to. We overload this in order to wrap in inside a
599 L</execute_reliably> method.
603 around 'txn_do' => sub {
604 my($txn_do, $self, $coderef, @args) = @_;
605 $self->execute_reliably(sub {$self->$txn_do($coderef, @args)});
610 Check that the master and at least one of the replicants is connected.
617 $self->master->connected &&
618 $self->pool->connected_replicants;
621 =head2 ensure_connected
623 Make sure all the storages are connected.
627 sub ensure_connected {
629 foreach my $source ($self->all_storages) {
630 $source->ensure_connected(@_);
636 Set the limit_dialect for all existing storages
642 foreach my $source ($self->all_storages) {
643 $source->limit_dialect(@_);
645 return $self->master->quote_char;
650 Set the quote_char for all existing storages
656 foreach my $source ($self->all_storages) {
657 $source->quote_char(@_);
659 return $self->master->quote_char;
664 Set the name_sep for all existing storages
670 foreach my $source ($self->all_storages) {
671 $source->name_sep(@_);
673 return $self->master->name_sep;
678 Set the schema object for all existing storages
684 foreach my $source ($self->all_storages) {
685 $source->set_schema(@_);
691 set a debug flag across all storages
698 foreach my $source ($self->all_storages) {
702 return $self->master->debug;
707 set a debug object across all storages
714 foreach my $source ($self->all_storages) {
715 $source->debugobj(@_);
718 return $self->master->debugobj;
723 set a debugfh object across all storages
730 foreach my $source ($self->all_storages) {
731 $source->debugfh(@_);
734 return $self->master->debugfh;
739 set a debug callback across all storages
746 foreach my $source ($self->all_storages) {
747 $source->debugcb(@_);
750 return $self->master->debugcb;
755 disconnect everything
761 foreach my $source ($self->all_storages) {
762 $source->disconnect(@_);
768 set cursor class on all storages, or return master's
773 my ($self, $cursor_class) = @_;
776 $_->cursor_class($cursor_class) for $self->all_storages;
778 $self->master->cursor_class;
783 Due to the fact that replicants can lag behind a master, you must take care to
784 make sure you use one of the methods to force read queries to a master should
785 you need realtime data integrity. For example, if you insert a row, and then
786 immediately re-read it from the database (say, by doing $row->discard_changes)
787 or you insert a row and then immediately build a query that expects that row
788 to be an item, you should force the master to handle reads. Otherwise, due to
789 the lag, there is no certainty your data will be in the expected state.
791 For data integrity, all transactions automatically use the master storage for
792 all read and write queries. Using a transaction is the preferred and recommended
793 method to force the master to handle all read queries.
795 Otherwise, you can force a single query to use the master with the 'force_pool'
798 my $row = $resultset->search(undef, {force_pool=>'master'})->find($pk);
800 This attribute will safely be ignore by non replicated storages, so you can use
801 the same code for both types of systems.
803 Lastly, you can use the L</execute_reliably> method, which works very much like
806 For debugging, you can turn replication on/off with the methods L</set_reliable_storage>
807 and L</set_balanced_storage>, however this operates at a global level and is not
808 suitable if you have a shared Schema object being used by multiple processes,
809 such as on a web application server. You can get around this limitation by
810 using the Schema clone method.
812 my $new_schema = $schema->clone;
813 $new_schema->set_reliable_storage;
815 ## $new_schema will use only the Master storage for all reads/writes while
816 ## the $schema object will use replicated storage.
820 John Napiorkowski <john.napiorkowski@takkle.com>
822 Based on code originated by:
824 Norbert Csongrádi <bert@cpan.org>
825 Peter Siklósi <einon@einon.hu>
829 You may distribute this code under the same terms as Perl itself.
833 __PACKAGE__->meta->make_immutable;