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1 | package DBIx::Class::Storage::DBI::Replicated::Pool; |
2 | |
3 | use Moose; |
4 | use MooseX::AttributeHelpers; |
5 | use DBIx::Class::Storage::DBI::Replicated::Replicant; |
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6 | use List::Util 'sum'; |
7 | use Scalar::Util 'reftype'; |
8 | use Carp::Clan qw/^DBIx::Class/; |
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9 | use MooseX::Types::Moose qw/Num Int ClassName HashRef/; |
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10 | |
11 | use namespace::clean -except => 'meta'; |
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12 | |
13 | =head1 NAME |
14 | |
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15 | DBIx::Class::Storage::DBI::Replicated::Pool - Manage a pool of replicants |
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16 | |
17 | =head1 SYNOPSIS |
18 | |
19 | This class is used internally by L<DBIx::Class::Storage::DBI::Replicated>. You |
20 | shouldn't need to create instances of this class. |
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21 | |
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22 | =head1 DESCRIPTION |
23 | |
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. |
27 | |
28 | =head1 ATTRIBUTES |
29 | |
30 | This class defines the following attributes. |
31 | |
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32 | =head2 maximum_lag ($num) |
33 | |
34 | This is a number which defines the maximum allowed lag returned by the |
35 | L<DBIx::Class::Storage::DBI/lag_behind_master> method. The default is 0. In |
36 | general, this should return a larger number when the replicant is lagging |
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37 | behind its master, however the implementation of this is database specific, so |
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38 | don't count on this number having a fixed meaning. For example, MySQL will |
39 | return a number of seconds that the replicating database is lagging. |
40 | |
41 | =cut |
42 | |
43 | has 'maximum_lag' => ( |
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44 | is=>'rw', |
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45 | isa=>Num, |
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46 | required=>1, |
47 | lazy=>1, |
48 | default=>0, |
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49 | ); |
50 | |
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51 | =head2 last_validated |
52 | |
53 | This is an integer representing a time since the last time the replicants were |
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54 | validated. It's nothing fancy, just an integer provided via the perl L<time|perlfunc/time> |
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55 | builtin. |
56 | |
57 | =cut |
58 | |
59 | has 'last_validated' => ( |
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60 | is=>'rw', |
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61 | isa=>Int, |
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62 | reader=>'last_validated', |
63 | writer=>'_last_validated', |
64 | lazy=>1, |
65 | default=>0, |
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66 | ); |
67 | |
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68 | =head2 replicant_type ($classname) |
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69 | |
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. |
73 | |
74 | =cut |
75 | |
76 | has 'replicant_type' => ( |
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77 | is=>'ro', |
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78 | isa=>ClassName, |
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79 | required=>1, |
80 | default=>'DBIx::Class::Storage::DBI', |
81 | handles=>{ |
82 | 'create_replicant' => 'new', |
83 | }, |
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84 | ); |
85 | |
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86 | =head2 replicants |
87 | |
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: |
90 | |
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91 | "dbi:SQLite:dbname=dbfile" |
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92 | |
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93 | You could access the specific replicant via: |
94 | |
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95 | $schema->storage->replicants->{'dbname=dbfile'} |
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96 | |
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97 | This attributes also supports the following helper methods: |
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98 | |
99 | =over 4 |
100 | |
101 | =item set_replicant($key=>$storage) |
102 | |
103 | Pushes a replicant onto the HashRef under $key |
104 | |
105 | =item get_replicant($key) |
106 | |
107 | Retrieves the named replicant |
108 | |
109 | =item has_replicants |
110 | |
111 | Returns true if the Pool defines replicants. |
112 | |
113 | =item num_replicants |
114 | |
115 | The number of replicants in the pool |
116 | |
117 | =item delete_replicant ($key) |
118 | |
119 | removes the replicant under $key from the pool |
120 | |
121 | =back |
122 | |
123 | =cut |
124 | |
125 | has 'replicants' => ( |
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126 | is=>'rw', |
127 | metaclass => 'Collection::Hash', |
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128 | isa=>HashRef['Object'], |
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129 | default=>sub {{}}, |
130 | provides => { |
131 | 'set' => 'set_replicant', |
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132 | 'get' => 'get_replicant', |
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133 | 'empty' => 'has_replicants', |
134 | 'count' => 'num_replicants', |
135 | 'delete' => 'delete_replicant', |
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136 | 'values' => 'all_replicant_storages', |
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137 | }, |
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138 | ); |
139 | |
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140 | =head1 METHODS |
141 | |
142 | This class defines the following methods. |
143 | |
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144 | =head2 connect_replicants ($schema, Array[$connect_info]) |
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145 | |
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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. |
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149 | |
150 | =cut |
151 | |
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152 | sub connect_replicants { |
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153 | my $self = shift @_; |
154 | my $schema = shift @_; |
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155 | |
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156 | my @newly_created = (); |
157 | foreach my $connect_info (@_) { |
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158 | $connect_info = [ $connect_info ] |
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159 | if reftype $connect_info ne 'ARRAY'; |
160 | |
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161 | croak "coderef replicant connect_info not supported" |
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162 | if ref $connect_info->[0] && reftype $connect_info->[0] eq 'CODE'; |
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163 | |
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164 | my $replicant = $self->connect_replicant($schema, $connect_info); |
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165 | |
166 | my $key = $connect_info->[0]; |
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167 | $key = $key->{dsn} if ref $key && reftype $key eq 'HASH'; |
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168 | ($key) = ($key =~ m/^dbi\:.+\:(.+)$/); |
169 | |
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170 | $self->set_replicant( $key => $replicant); |
171 | push @newly_created, $replicant; |
172 | } |
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173 | |
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174 | return @newly_created; |
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175 | } |
176 | |
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177 | =head2 connect_replicant ($schema, $connect_info) |
178 | |
179 | Given a schema object and a hashref of $connect_info, connect the replicant |
180 | and return it. |
181 | |
182 | =cut |
183 | |
184 | sub connect_replicant { |
185 | my ($self, $schema, $connect_info) = @_; |
186 | my $replicant = $self->create_replicant($schema); |
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187 | $replicant->connect_info($connect_info); |
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188 | |
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 |
193 | ## may fail. |
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194 | ## |
195 | ## Why this is necessary at all, is that we need to have the final storage |
196 | ## class to apply the Replicant role. |
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197 | |
198 | $self->_safely($replicant, '->_determine_driver', sub { |
199 | $replicant->_determine_driver |
200 | }); |
201 | |
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202 | DBIx::Class::Storage::DBI::Replicated::Replicant->meta->apply($replicant); |
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203 | return $replicant; |
204 | } |
205 | |
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206 | =head2 _safely_ensure_connected ($replicant) |
207 | |
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 |
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212 | way a slave can go completely offline (ie, the box itself can die) without |
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213 | bringing down your entire pool of databases. |
214 | |
215 | =cut |
216 | |
217 | sub _safely_ensure_connected { |
218 | my ($self, $replicant, @args) = @_; |
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219 | |
220 | return $self->_safely($replicant, '->ensure_connected', sub { |
221 | $replicant->ensure_connected(@args) |
222 | }); |
223 | } |
224 | |
225 | =head2 _safely ($replicant, $name, $code) |
226 | |
227 | Execute C<$code> for operation C<$name> catching any exceptions and printing an |
228 | error message to the C<<$replicant->debugobj>>. |
229 | |
230 | Returns 1 on success and undef on failure. |
231 | |
232 | =cut |
233 | |
234 | sub _safely { |
235 | my ($self, $replicant, $name, $code) = @_; |
236 | |
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237 | eval { |
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238 | $code->() |
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239 | }; |
240 | if ($@) { |
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241 | $replicant |
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242 | ->debugobj |
243 | ->print( |
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244 | sprintf( "Exception trying to $name for replicant %s, error is %s", |
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245 | $replicant->_dbi_connect_info->[0], $@) |
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246 | ); |
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247 | return; |
13b9e828 |
248 | } |
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249 | return 1; |
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250 | } |
251 | |
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252 | =head2 connected_replicants |
253 | |
254 | Returns true if there are connected replicants. Actually is overloaded to |
255 | return the number of replicants. So you can do stuff like: |
256 | |
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257 | if( my $num_connected = $storage->has_connected_replicants ) { |
258 | print "I have $num_connected connected replicants"; |
259 | } else { |
260 | print "Sorry, no replicants."; |
261 | } |
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262 | |
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. |
265 | |
266 | =cut |
267 | |
268 | sub connected_replicants { |
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269 | my $self = shift @_; |
270 | return sum( map { |
271 | $_->connected ? 1:0 |
272 | } $self->all_replicants ); |
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273 | } |
274 | |
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275 | =head2 active_replicants |
276 | |
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. |
280 | |
281 | =cut |
282 | |
283 | sub active_replicants { |
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284 | my $self = shift @_; |
285 | return ( grep {$_} map { |
286 | $_->active ? $_:0 |
287 | } $self->all_replicants ); |
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288 | } |
289 | |
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290 | =head2 all_replicants |
291 | |
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. |
294 | |
295 | =cut |
296 | |
297 | sub all_replicants { |
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298 | my $self = shift @_; |
299 | return values %{$self->replicants}; |
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300 | } |
301 | |
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302 | =head2 validate_replicants |
303 | |
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. |
308 | |
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. |
311 | |
312 | See L<DBIx::Class::Storage::DBI> for more about checking if a replicating |
313 | connection is not following a master or is lagging. |
314 | |
315 | Calling this method will generate queries on the replicant databases so it is |
316 | not recommended that you run them very often. |
317 | |
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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. |
321 | |
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322 | =cut |
323 | |
324 | sub validate_replicants { |
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325 | my $self = shift @_; |
326 | foreach my $replicant($self->all_replicants) { |
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327 | if($self->_safely_ensure_connected($replicant)) { |
328 | my $is_replicating = $replicant->is_replicating; |
329 | unless(defined $is_replicating) { |
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330 | $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'is_replicating' method. Assuming you are manually managing.\n"); |
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331 | next; |
332 | } else { |
333 | if($is_replicating) { |
334 | my $lag_behind_master = $replicant->lag_behind_master; |
335 | unless(defined $lag_behind_master) { |
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336 | $replicant->debugobj->print("Storage Driver ".ref($self)." Does not support the 'lag_behind_master' method. Assuming you are manually managing.\n"); |
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337 | next; |
338 | } else { |
339 | if($lag_behind_master <= $self->maximum_lag) { |
340 | $replicant->active(1); |
341 | } else { |
342 | $replicant->active(0); |
343 | } |
344 | } |
345 | } else { |
346 | $replicant->active(0); |
347 | } |
348 | } |
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349 | } else { |
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350 | $replicant->active(0); |
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351 | } |
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352 | } |
353 | ## Mark that we completed this validation. |
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354 | $self->_last_validated(time); |
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355 | } |
356 | |
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357 | =head1 AUTHOR |
358 | |
359 | John Napiorkowski <john.napiorkowski@takkle.com> |
360 | |
361 | =head1 LICENSE |
362 | |
363 | You may distribute this code under the same terms as Perl itself. |
364 | |
365 | =cut |
366 | |
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367 | __PACKAGE__->meta->make_immutable; |
368 | |
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369 | 1; |