1 package DBIx::Class::Storage::DBI::Replicated::Pool;
4 use MooseX::AttributeHelpers;
5 use DBIx::Class::Storage::DBI::Replicated::Replicant;
7 use Scalar::Util 'reftype';
8 use Carp::Clan qw/^DBIx::Class/;
9 use MooseX::Types::Moose qw/Num Int ClassName HashRef/;
11 use namespace::clean -except => 'meta';
15 DBIx::Class::Storage::DBI::Replicated::Pool - Manage a pool of replicants
19 This class is used internally by L<DBIx::Class::Storage::DBI::Replicated>. You
20 shouldn't need to create instances of this class.
24 In a replicated storage type, there is at least one replicant to handle the
25 read only traffic. The Pool class manages this replicant, or list of
26 replicants, and gives some methods for querying information about their status.
30 This class defines the following attributes.
32 =head2 maximum_lag ($num)
34 This is a number which defines the maximum allowed lag returned by the
35 L<DBIx::Class::Storage::DBI/lag_behind_master> method. The default is 0. In
36 general, this should return a larger number when the replicant is lagging
37 behind its master, however the implementation of this is database specific, so
38 don't count on this number having a fixed meaning. For example, MySQL will
39 return a number of seconds that the replicating database is lagging.
43 has 'maximum_lag' => (
53 This is an integer representing a time since the last time the replicants were
54 validated. It's nothing fancy, just an integer provided via the perl L<time|perlfunc/time>
59 has 'last_validated' => (
62 reader=>'last_validated',
63 writer=>'_last_validated',
68 =head2 replicant_type ($classname)
70 Base class used to instantiate replicants that are in the pool. Unless you
71 need to subclass L<DBIx::Class::Storage::DBI::Replicated::Replicant> you should
72 just leave this alone.
76 has 'replicant_type' => (
80 default=>'DBIx::Class::Storage::DBI',
82 'create_replicant' => 'new',
88 A hashref of replicant, with the key being the dsn and the value returning the
89 actual replicant storage. For example if the $dsn element is something like:
91 "dbi:SQLite:dbname=dbfile"
93 You could access the specific replicant via:
95 $schema->storage->replicants->{'dbname=dbfile'}
97 This attributes also supports the following helper methods:
101 =item set_replicant($key=>$storage)
103 Pushes a replicant onto the HashRef under $key
105 =item get_replicant($key)
107 Retrieves the named replicant
111 Returns true if the Pool defines replicants.
115 The number of replicants in the pool
117 =item delete_replicant ($key)
119 removes the replicant under $key from the pool
125 has 'replicants' => (
127 metaclass => 'Collection::Hash',
128 isa=>HashRef['Object'],
131 'set' => 'set_replicant',
132 'get' => 'get_replicant',
133 'empty' => 'has_replicants',
134 'count' => 'num_replicants',
135 'delete' => 'delete_replicant',
136 'values' => 'all_replicant_storages',
142 This class defines the following methods.
144 =head2 connect_replicants ($schema, Array[$connect_info])
146 Given an array of $dsn or connect_info structures suitable for connected to a
147 database, create an L<DBIx::Class::Storage::DBI::Replicated::Replicant> object
148 and store it in the L</replicants> attribute.
152 sub connect_replicants {
154 my $schema = shift @_;
156 my @newly_created = ();
157 foreach my $connect_info (@_) {
158 $connect_info = [ $connect_info ]
159 if reftype $connect_info ne 'ARRAY';
161 croak "coderef replicant connect_info not supported"
162 if ref $connect_info->[0] && reftype $connect_info->[0] eq 'CODE';
164 my $replicant = $self->connect_replicant($schema, $connect_info);
166 my $key = $connect_info->[0];
167 $key = $key->{dsn} if ref $key && reftype $key eq 'HASH';
168 ($key) = ($key =~ m/^dbi\:.+\:(.+)$/);
170 $self->set_replicant( $key => $replicant);
171 push @newly_created, $replicant;
174 return @newly_created;
177 =head2 connect_replicant ($schema, $connect_info)
179 Given a schema object and a hashref of $connect_info, connect the replicant
184 sub connect_replicant {
185 my ($self, $schema, $connect_info) = @_;
186 my $replicant = $self->create_replicant($schema);
187 $replicant->connect_info($connect_info);
189 ## It is undesirable for catalyst to connect at ->conect_replicants time, as
190 ## connections should only happen on the first request that uses the database.
191 ## So we try to set the driver without connecting, however this doesn't always
192 ## work, as a driver may need to connect to determine the DB version, and this
195 ## Why this is necessary at all, is that we need to have the final storage
196 ## class to apply the Replicant role.
198 $self->_safely($replicant, '->_determine_driver', sub {
199 $replicant->_determine_driver
202 DBIx::Class::Storage::DBI::Replicated::Replicant->meta->apply($replicant);
206 =head2 _safely_ensure_connected ($replicant)
208 The standard ensure_connected method with throw an exception should it fail to
209 connect. For the master database this is desirable, but since replicants are
210 allowed to fail, this behavior is not desirable. This method wraps the call
211 to ensure_connected in an eval in order to catch any generated errors. That
212 way a slave can go completely offline (ie, the box itself can die) without
213 bringing down your entire pool of databases.
217 sub _safely_ensure_connected {
218 my ($self, $replicant, @args) = @_;
220 return $self->_safely($replicant, '->ensure_connected', sub {
221 $replicant->ensure_connected(@args)
225 =head2 _safely ($replicant, $name, $code)
227 Execute C<$code> for operation C<$name> catching any exceptions and printing an
228 error message to the C<<$replicant->debugobj>>.
230 Returns 1 on success and undef on failure.
235 my ($self, $replicant, $name, $code) = @_;
244 sprintf( "Exception trying to $name for replicant %s, error is %s",
245 $replicant->_dbi_connect_info->[0], $@)
252 =head2 connected_replicants
254 Returns true if there are connected replicants. Actually is overloaded to
255 return the number of replicants. So you can do stuff like:
257 if( my $num_connected = $storage->has_connected_replicants ) {
258 print "I have $num_connected connected replicants";
260 print "Sorry, no replicants.";
263 This method will actually test that each replicant in the L</replicants> hashref
264 is actually connected, try not to hit this 10 times a second.
268 sub connected_replicants {
272 } $self->all_replicants );
275 =head2 active_replicants
277 This is an array of replicants that are considered to be active in the pool.
278 This does not check to see if they are connected, but if they are not, DBIC
279 should automatically reconnect them for us when we hit them with a query.
283 sub active_replicants {
285 return ( grep {$_} map {
287 } $self->all_replicants );
290 =head2 all_replicants
292 Just a simple array of all the replicant storages. No particular order to the
293 array is given, nor should any meaning be derived.
299 return values %{$self->replicants};
302 =head2 validate_replicants
304 This does a check to see if 1) each replicate is connected (or reconnectable),
305 2) that is ->is_replicating, and 3) that it is not exceeding the lag amount
306 defined by L</maximum_lag>. Replicants that fail any of these tests are set to
307 inactive, and thus removed from the replication pool.
309 This tests L<all_replicants>, since a replicant that has been previous marked
310 as inactive can be reactived should it start to pass the validation tests again.
312 See L<DBIx::Class::Storage::DBI> for more about checking if a replicating
313 connection is not following a master or is lagging.
315 Calling this method will generate queries on the replicant databases so it is
316 not recommended that you run them very often.
318 This method requires that your underlying storage engine supports some sort of
319 native replication mechanism. Currently only MySQL native replication is
320 supported. Your patches to make other replication types work are welcomed.
324 sub validate_replicants {
326 foreach my $replicant($self->all_replicants) {
327 if($self->_safely_ensure_connected($replicant)) {
328 my $is_replicating = $replicant->is_replicating;
329 unless(defined $is_replicating) {
330 $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'is_replicating' method. Assuming you are manually managing.\n");
333 if($is_replicating) {
334 my $lag_behind_master = $replicant->lag_behind_master;
335 unless(defined $lag_behind_master) {
336 $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'lag_behind_master' method. Assuming you are manually managing.\n");
339 if($lag_behind_master <= $self->maximum_lag) {
340 $replicant->active(1);
342 $replicant->active(0);
346 $replicant->active(0);
350 $replicant->active(0);
353 ## Mark that we completed this validation.
354 $self->_last_validated(time);
359 John Napiorkowski <john.napiorkowski@takkle.com>
363 You may distribute this code under the same terms as Perl itself.
367 __PACKAGE__->meta->make_immutable;