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1 | package DBIx::Class::Storage::DBI::Replicated::Balancer; |
2 | |
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3 | use Moose::Role; |
4 | requires 'next_storage'; |
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5 | use MooseX::Types::Moose qw/Int/; |
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6 | use DBIx::Class::Storage::DBI::Replicated::Pool; |
7 | use DBIx::Class::Storage::DBI::Replicated::Types qw/DBICStorageDBI/; |
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8 | use namespace::clean -except => 'meta'; |
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9 | |
10 | =head1 NAME |
11 | |
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12 | DBIx::Class::Storage::DBI::Replicated::Balancer - A Software Load Balancer |
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13 | |
14 | =head1 SYNOPSIS |
15 | |
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16 | This role is used internally by L<DBIx::Class::Storage::DBI::Replicated>. |
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17 | |
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18 | =head1 DESCRIPTION |
19 | |
20 | Given a pool (L<DBIx::Class::Storage::DBI::Replicated::Pool>) of replicated |
21 | database's (L<DBIx::Class::Storage::DBI::Replicated::Replicant>), defines a |
22 | method by which query load can be spread out across each replicant in the pool. |
23 | |
24 | =head1 ATTRIBUTES |
25 | |
26 | This class defines the following attributes. |
27 | |
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28 | =head2 auto_validate_every ($seconds) |
29 | |
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30 | If auto_validate has some sort of value, run |
31 | L<DBIx::Class::Storage::DBI::Replicated::Pool/validate_replicants> |
32 | every $seconds. Be careful with this, because if you set it to 0 you |
33 | will end up validating every query. |
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34 | |
35 | =cut |
36 | |
37 | has 'auto_validate_every' => ( |
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38 | is=>'rw', |
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39 | isa=>Int, |
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40 | predicate=>'has_auto_validate_every', |
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41 | ); |
42 | |
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43 | =head2 master |
44 | |
45 | The L<DBIx::Class::Storage::DBI> object that is the master database all the |
46 | replicants are trying to follow. The balancer needs to know it since it's the |
47 | ultimate fallback. |
48 | |
49 | =cut |
50 | |
51 | has 'master' => ( |
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52 | is=>'ro', |
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53 | isa=>DBICStorageDBI, |
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54 | required=>1, |
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55 | ); |
56 | |
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57 | =head2 pool |
58 | |
59 | The L<DBIx::Class::Storage::DBI::Replicated::Pool> object that we are trying to |
60 | balance. |
61 | |
62 | =cut |
63 | |
64 | has 'pool' => ( |
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65 | is=>'ro', |
66 | isa=>'DBIx::Class::Storage::DBI::Replicated::Pool', |
67 | required=>1, |
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68 | ); |
69 | |
70 | =head2 current_replicant |
71 | |
72 | Replicant storages (slaves) handle all read only traffic. The assumption is |
73 | that your database will become readbound well before it becomes write bound |
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74 | and that being able to spread your read only traffic around to multiple |
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75 | databases is going to help you to scale traffic. |
76 | |
77 | This attribute returns the next slave to handle a read request. Your L</pool> |
78 | attribute has methods to help you shuffle through all the available replicants |
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79 | via its balancer object. |
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80 | |
81 | =cut |
82 | |
83 | has 'current_replicant' => ( |
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84 | is=> 'rw', |
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85 | isa=>DBICStorageDBI, |
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86 | lazy_build=>1, |
87 | handles=>[qw/ |
88 | select |
89 | select_single |
90 | columns_info_for |
91 | /], |
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92 | ); |
93 | |
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94 | =head1 METHODS |
95 | |
96 | This class defines the following methods. |
97 | |
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98 | =head2 _build_current_replicant |
99 | |
100 | Lazy builder for the L</current_replicant_storage> attribute. |
101 | |
102 | =cut |
103 | |
104 | sub _build_current_replicant { |
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105 | my $self = shift @_; |
106 | $self->next_storage; |
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107 | } |
108 | |
109 | =head2 next_storage |
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110 | |
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111 | This method should be defined in the class which consumes this role. |
112 | |
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113 | Given a pool object, return the next replicant that will serve queries. The |
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114 | default behavior is to grab the first replicant it finds but you can write |
115 | your own subclasses of L<DBIx::Class::Storage::DBI::Replicated::Balancer> to |
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116 | support other balance systems. |
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117 | |
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118 | This returns from the pool of active replicants. If there are no active |
119 | replicants, then you should have it return the master as an ultimate fallback. |
120 | |
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121 | =head2 around: next_storage |
122 | |
123 | Advice on next storage to add the autovalidation. We have this broken out so |
124 | that it's easier to break out the auto validation into a role. |
125 | |
126 | This also returns the master in the case that none of the replicants are active |
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127 | or just forgot to create them :) |
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128 | |
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129 | =cut |
130 | |
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131 | my $on_master; |
132 | |
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133 | around 'next_storage' => sub { |
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134 | my ($next_storage, $self, @args) = @_; |
135 | my $now = time; |
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136 | |
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137 | ## Do we need to validate the replicants? |
138 | if( |
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139 | $self->has_auto_validate_every && |
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140 | ($self->auto_validate_every + $self->pool->last_validated) <= $now |
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141 | ) { |
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142 | $self->pool->validate_replicants; |
143 | } |
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144 | |
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145 | ## Get a replicant, or the master if none |
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146 | if(my $next = $self->$next_storage(@args)) { |
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147 | $self->master->debugobj->print("Moved back to slave\n") if $on_master; |
148 | $on_master = 0; |
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149 | return $next; |
150 | } else { |
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151 | $self->master->debugobj->print("No Replicants validate, falling back to master reads.\n") |
152 | unless $on_master++; |
153 | |
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154 | return $self->master; |
155 | } |
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156 | }; |
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157 | |
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158 | =head2 increment_storage |
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159 | |
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160 | Rolls the Storage to whatever is next in the queue, as defined by the Balancer. |
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161 | |
162 | =cut |
163 | |
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164 | sub increment_storage { |
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165 | my $self = shift @_; |
166 | my $next_replicant = $self->next_storage; |
167 | $self->current_replicant($next_replicant); |
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168 | } |
169 | |
170 | =head2 around: select |
171 | |
172 | Advice on the select attribute. Each time we use a replicant |
173 | we need to change it via the storage pool algorithm. That way we are spreading |
174 | the load evenly (hopefully) across existing capacity. |
175 | |
176 | =cut |
177 | |
178 | around 'select' => sub { |
179 | my ($select, $self, @args) = @_; |
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180 | |
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181 | if (my $forced_pool = $args[-1]->{force_pool}) { |
182 | delete $args[-1]->{force_pool}; |
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183 | return $self->_get_forced_pool($forced_pool)->select(@args); |
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184 | } elsif($self->master->{transaction_depth}) { |
185 | return $self->master->select(@args); |
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186 | } else { |
187 | $self->increment_storage; |
188 | return $self->$select(@args); |
189 | } |
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190 | }; |
191 | |
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192 | =head2 around: select_single |
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193 | |
194 | Advice on the select_single attribute. Each time we use a replicant |
195 | we need to change it via the storage pool algorithm. That way we are spreading |
196 | the load evenly (hopefully) across existing capacity. |
197 | |
198 | =cut |
199 | |
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200 | around 'select_single' => sub { |
201 | my ($select_single, $self, @args) = @_; |
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202 | |
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203 | if (my $forced_pool = $args[-1]->{force_pool}) { |
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204 | delete $args[-1]->{force_pool}; |
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205 | return $self->_get_forced_pool($forced_pool)->select_single(@args); |
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206 | } elsif($self->master->{transaction_depth}) { |
207 | return $self->master->select_single(@args); |
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208 | } else { |
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209 | $self->increment_storage; |
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210 | return $self->$select_single(@args); |
211 | } |
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212 | }; |
213 | |
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214 | =head2 before: columns_info_for |
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215 | |
216 | Advice on the current_replicant_storage attribute. Each time we use a replicant |
217 | we need to change it via the storage pool algorithm. That way we are spreading |
218 | the load evenly (hopefully) across existing capacity. |
219 | |
220 | =cut |
221 | |
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222 | before 'columns_info_for' => sub { |
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223 | my $self = shift @_; |
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224 | $self->increment_storage; |
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225 | }; |
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226 | |
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227 | =head2 _get_forced_pool ($name) |
228 | |
229 | Given an identifier, find the most correct storage object to handle the query. |
230 | |
231 | =cut |
232 | |
233 | sub _get_forced_pool { |
234 | my ($self, $forced_pool) = @_; |
235 | if(blessed $forced_pool) { |
236 | return $forced_pool; |
237 | } elsif($forced_pool eq 'master') { |
238 | return $self->master; |
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239 | } elsif(my $replicant = $self->pool->replicants->{$forced_pool}) { |
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240 | return $replicant; |
241 | } else { |
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242 | $self->master->throw_exception("'$forced_pool' is not a named replicant."); |
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243 | } |
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244 | } |
245 | |
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246 | =head1 AUTHOR |
247 | |
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248 | John Napiorkowski <jjnapiork@cpan.org> |
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249 | |
250 | =head1 LICENSE |
251 | |
252 | You may distribute this code under the same terms as Perl itself. |
253 | |
254 | =cut |
255 | |
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256 | 1; |