1 package DBIx::Class::Storage::DBI::Replicated::Pool;
4 use DBIx::Class::Storage::DBI::Replicated::Replicant;
6 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 $key from the pool
125 has 'replicants' => (
128 isa=>HashRef['Object'],
131 'set_replicant' => 'set',
132 'get_replicant' => 'get',
133 'has_replicants' => 'is_empty',
134 'num_replicants' => 'count',
135 'delete_replicant' => 'delete',
136 'all_replicant_storages' => 'values',
140 around has_replicants => sub {
141 my ($orig, $self) = @_;
142 return !$self->$orig;
145 has next_unknown_replicant_id => (
147 traits => ['Counter'],
151 'inc_unknown_replicant_id' => 'inc',
157 This class defines the following methods.
159 =head2 connect_replicants ($schema, Array[$connect_info])
161 Given an array of $dsn or connect_info structures suitable for connected to a
162 database, create an L<DBIx::Class::Storage::DBI::Replicated::Replicant> object
163 and store it in the L</replicants> attribute.
167 sub connect_replicants {
169 my $schema = shift @_;
171 my @newly_created = ();
172 foreach my $connect_info (@_) {
173 $connect_info = [ $connect_info ]
174 if reftype $connect_info ne 'ARRAY';
176 my $connect_coderef =
177 (reftype($connect_info->[0])||'') eq 'CODE' ? $connect_info->[0]
178 : (reftype($connect_info->[0])||'') eq 'HASH' &&
179 $connect_info->[0]->{dbh_maker};
183 # yes this is evil, but it only usually happens once (for coderefs)
184 # this will fail if the coderef does not actually DBI::connect
185 no warnings 'redefine';
186 my $connect = \&DBI::connect;
187 local *DBI::connect = sub {
191 $self->connect_replicant($schema, $connect_info);
197 if (!$connect_coderef) {
198 $dsn = $connect_info->[0];
199 $dsn = $dsn->{dsn} if (reftype($dsn)||'') eq 'HASH';
202 # all attempts to get the DSN failed
203 $key = "UNKNOWN_" . $self->next_unknown_replicant_id;
204 $self->inc_unknown_replicant_id;
208 $replicant->dsn($dsn);
209 ($key) = ($dsn =~ m/^dbi\:.+\:(.+)$/i);
212 $replicant->id($key);
213 $self->set_replicant($key => $replicant);
215 push @newly_created, $replicant;
218 return @newly_created;
221 =head2 connect_replicant ($schema, $connect_info)
223 Given a schema object and a hashref of $connect_info, connect the replicant
228 sub connect_replicant {
229 my ($self, $schema, $connect_info) = @_;
230 my $replicant = $self->create_replicant($schema);
231 $replicant->connect_info($connect_info);
233 ## It is undesirable for catalyst to connect at ->conect_replicants time, as
234 ## connections should only happen on the first request that uses the database.
235 ## So we try to set the driver without connecting, however this doesn't always
236 ## work, as a driver may need to connect to determine the DB version, and this
239 ## Why this is necessary at all, is that we need to have the final storage
240 ## class to apply the Replicant role.
242 $self->_safely($replicant, '->_determine_driver', sub {
243 $replicant->_determine_driver
246 DBIx::Class::Storage::DBI::Replicated::Replicant->meta->apply($replicant);
250 =head2 _safely_ensure_connected ($replicant)
252 The standard ensure_connected method with throw an exception should it fail to
253 connect. For the master database this is desirable, but since replicants are
254 allowed to fail, this behavior is not desirable. This method wraps the call
255 to ensure_connected in an eval in order to catch any generated errors. That
256 way a slave can go completely offline (ie, the box itself can die) without
257 bringing down your entire pool of databases.
261 sub _safely_ensure_connected {
262 my ($self, $replicant, @args) = @_;
264 return $self->_safely($replicant, '->ensure_connected', sub {
265 $replicant->ensure_connected(@args)
269 =head2 _safely ($replicant, $name, $code)
271 Execute C<$code> for operation C<$name> catching any exceptions and printing an
272 error message to the C<<$replicant->debugobj>>.
274 Returns 1 on success and undef on failure.
279 my ($self, $replicant, $name, $code) = @_;
288 sprintf( "Exception trying to $name for replicant %s, error is %s",
289 $replicant->_dbi_connect_info->[0], $@)
296 =head2 connected_replicants
298 Returns true if there are connected replicants. Actually is overloaded to
299 return the number of replicants. So you can do stuff like:
301 if( my $num_connected = $storage->has_connected_replicants ) {
302 print "I have $num_connected connected replicants";
304 print "Sorry, no replicants.";
307 This method will actually test that each replicant in the L</replicants> hashref
308 is actually connected, try not to hit this 10 times a second.
312 sub connected_replicants {
316 } $self->all_replicants );
319 =head2 active_replicants
321 This is an array of replicants that are considered to be active in the pool.
322 This does not check to see if they are connected, but if they are not, DBIC
323 should automatically reconnect them for us when we hit them with a query.
327 sub active_replicants {
329 return ( grep {$_} map {
331 } $self->all_replicants );
334 =head2 all_replicants
336 Just a simple array of all the replicant storages. No particular order to the
337 array is given, nor should any meaning be derived.
343 return values %{$self->replicants};
346 =head2 validate_replicants
348 This does a check to see if 1) each replicate is connected (or reconnectable),
349 2) that is ->is_replicating, and 3) that it is not exceeding the lag amount
350 defined by L</maximum_lag>. Replicants that fail any of these tests are set to
351 inactive, and thus removed from the replication pool.
353 This tests L<all_replicants>, since a replicant that has been previous marked
354 as inactive can be reactived should it start to pass the validation tests again.
356 See L<DBIx::Class::Storage::DBI> for more about checking if a replicating
357 connection is not following a master or is lagging.
359 Calling this method will generate queries on the replicant databases so it is
360 not recommended that you run them very often.
362 This method requires that your underlying storage engine supports some sort of
363 native replication mechanism. Currently only MySQL native replication is
364 supported. Your patches to make other replication types work are welcomed.
368 sub validate_replicants {
370 foreach my $replicant($self->all_replicants) {
371 if($self->_safely_ensure_connected($replicant)) {
372 my $is_replicating = $replicant->is_replicating;
373 unless(defined $is_replicating) {
374 $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'is_replicating' method. Assuming you are manually managing.\n");
377 if($is_replicating) {
378 my $lag_behind_master = $replicant->lag_behind_master;
379 unless(defined $lag_behind_master) {
380 $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'lag_behind_master' method. Assuming you are manually managing.\n");
383 if($lag_behind_master <= $self->maximum_lag) {
384 $replicant->active(1);
386 $replicant->active(0);
390 $replicant->active(0);
394 $replicant->active(0);
397 ## Mark that we completed this validation.
398 $self->_last_validated(time);
403 John Napiorkowski <john.napiorkowski@takkle.com>
407 You may distribute this code under the same terms as Perl itself.
411 __PACKAGE__->meta->make_immutable;