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 ($num)
34 This is a number which defines the maximum allowed lag returned by the
35 L<DBIx::Class::Storage::DBI/lag_behind_master> method. The default is 0. In
36 general, this should return a larger number when the replicant is lagging
37 behind it's master, however the implementation of this is database specific, so
38 don't count on this number having a fixed meaning. For example, MySQL will
39 return a number of seconds that the replicating database is lagging.
43 has 'maximum_lag' => (
53 This is an integer representing a time since the last time the replicants were
54 validated. It's nothing fancy, just an integer provided via the perl time
59 has 'last_validated' => (
62 reader=>'last_validated',
63 writer=>'_last_validated',
68 =head2 replicant_type ($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 $key from the pool
125 has 'replicants' => (
127 metaclass => 'Collection::Hash',
128 isa=>HashRef['DBIx::Class::Storage::DBI'],
131 'set' => 'set_replicant',
132 'get' => 'get_replicant',
133 'empty' => 'has_replicants',
134 'count' => 'num_replicants',
135 'delete' => 'delete_replicant',
141 This class defines the following methods.
143 =head2 connect_replicants ($schema, Array[$connect_info])
145 Given an array of $dsn or connect_info structures suitable for connected to a
146 database, create an L<DBIx::Class::Storage::DBI::Replicated::Replicant> object
147 and store it in the L</replicants> attribute.
151 sub connect_replicants {
153 my $schema = shift @_;
155 my @newly_created = ();
156 foreach my $connect_info (@_) {
157 $connect_info = [ $connect_info ]
158 if reftype $connect_info ne 'ARRAY';
160 croak "coderef replicant connect_info not supported"
161 if ref $connect_info->[0] && reftype $connect_info->[0] eq 'CODE';
163 my $replicant = $self->connect_replicant($schema, $connect_info);
165 my $key = $connect_info->[0];
166 $key = $key->{dsn} if ref $key && reftype $key eq 'HASH';
167 ($key) = ($key =~ m/^dbi\:.+\:(.+)$/);
169 $self->set_replicant( $key => $replicant);
170 push @newly_created, $replicant;
173 return @newly_created;
176 =head2 connect_replicant ($schema, $connect_info)
178 Given a schema object and a hashref of $connect_info, connect the replicant
183 sub connect_replicant {
184 my ($self, $schema, $connect_info) = @_;
185 my $replicant = $self->create_replicant($schema);
186 $replicant->connect_info($connect_info);
188 ## It is undesirable for catalyst to connect at ->conect_replicants time, as
189 ## connections should only happen on the first request that uses the database.
190 ## So we try to set the driver without connecting, however this doesn't always
191 ## work, as a driver may need to connect to determine the DB version, and this
194 ## Why this is necessary at all, is that we need to have the final storage
195 ## class to apply the Replicant role.
197 $self->_safely($replicant, '->_determine_driver', sub {
198 $replicant->_determine_driver
201 DBIx::Class::Storage::DBI::Replicated::Replicant->meta->apply($replicant);
205 =head2 _safely_ensure_connected ($replicant)
207 The standard ensure_connected method with throw an exception should it fail to
208 connect. For the master database this is desirable, but since replicants are
209 allowed to fail, this behavior is not desirable. This method wraps the call
210 to ensure_connected in an eval in order to catch any generated errors. That
211 way a slave can go completely offline (ie, the box itself can die) without
212 bringing down your entire pool of databases.
216 sub _safely_ensure_connected {
217 my ($self, $replicant, @args) = @_;
219 return $self->_safely($replicant, '->ensure_connected', sub {
220 $replicant->ensure_connected(@args)
224 =head2 _safely ($replicant, $name, $code)
226 Execute C<$code> for operation C<$name> catching any exceptions and printing an
227 error message to the C<<$replicant->debugobj>>.
229 Returns 1 on success and undef on failure.
234 my ($self, $replicant, $name, $code) = @_;
243 sprintf( "Exception trying to $name for replicant %s, error is %s",
244 $replicant->_dbi_connect_info->[0], $@)
251 =head2 connected_replicants
253 Returns true if there are connected replicants. Actually is overloaded to
254 return the number of replicants. So you can do stuff like:
256 if( my $num_connected = $storage->has_connected_replicants ) {
257 print "I have $num_connected connected replicants";
259 print "Sorry, no replicants.";
262 This method will actually test that each replicant in the L</replicants> hashref
263 is actually connected, try not to hit this 10 times a second.
267 sub connected_replicants {
271 } $self->all_replicants );
274 =head2 active_replicants
276 This is an array of replicants that are considered to be active in the pool.
277 This does not check to see if they are connected, but if they are not, DBIC
278 should automatically reconnect them for us when we hit them with a query.
282 sub active_replicants {
284 return ( grep {$_} map {
286 } $self->all_replicants );
289 =head2 all_replicants
291 Just a simple array of all the replicant storages. No particular order to the
292 array is given, nor should any meaning be derived.
298 return values %{$self->replicants};
301 =head2 validate_replicants
303 This does a check to see if 1) each replicate is connected (or reconnectable),
304 2) that is ->is_replicating, and 3) that it is not exceeding the lag amount
305 defined by L</maximum_lag>. Replicants that fail any of these tests are set to
306 inactive, and thus removed from the replication pool.
308 This tests L<all_replicants>, since a replicant that has been previous marked
309 as inactive can be reactived should it start to pass the validation tests again.
311 See L<DBIx::Class::Storage::DBI> for more about checking if a replicating
312 connection is not following a master or is lagging.
314 Calling this method will generate queries on the replicant databases so it is
315 not recommended that you run them very often.
317 This method requires that your underlying storage engine supports some sort of
318 native replication mechanism. Currently only MySQL native replication is
319 supported. Your patches to make other replication types work are welcomed.
323 sub validate_replicants {
325 foreach my $replicant($self->all_replicants) {
326 if($self->_safely_ensure_connected($replicant)) {
327 my $is_replicating = $replicant->is_replicating;
328 unless(defined $is_replicating) {
329 $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'is_replicating' method. Assuming you are manually managing.\n");
332 if($is_replicating) {
333 my $lag_behind_master = $replicant->lag_behind_master;
334 unless(defined $lag_behind_master) {
335 $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'lag_behind_master' method. Assuming you are manually managing.\n");
338 if($lag_behind_master <= $self->maximum_lag) {
339 $replicant->active(1);
341 $replicant->active(0);
345 $replicant->active(0);
349 $replicant->active(0);
352 ## Mark that we completed this validation.
353 $self->_last_validated(time);
358 John Napiorkowski <john.napiorkowski@takkle.com>
362 You may distribute this code under the same terms as Perl itself.
366 __PACKAGE__->meta->make_immutable;