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1 | package DBIx::Class::Storage::DBI::Replicated::Balancer; |
2 | |
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3 | use Moo::Role; |
4 | use Scalar::Util (); |
5 | use DBIx::Class::Storage::DBI::Replicated::Types |
6 | qw(PositiveInteger DBICStorageDBI DBICStorageDBIReplicatedPool); |
7 | |
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8 | requires 'next_storage'; |
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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 | |
30 | If auto_validate has some sort of value, run the L<validate_replicants> every |
31 | $seconds. Be careful with this, because if you set it to 0 you will end up |
32 | validating every query. |
33 | |
34 | =cut |
35 | |
36 | has 'auto_validate_every' => ( |
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37 | is=>'rw', |
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38 | isa=>PositiveInteger, |
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39 | predicate=>'has_auto_validate_every', |
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40 | |
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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', |
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66 | isa=>DBICStorageDBIReplicatedPool, |
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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 |
74 | and that being able to spread your read only traffic around to multiple |
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=>1, |
87 | builder=>'_build_current_replicant', |
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88 | handles=>[qw/ |
89 | select |
90 | select_single |
91 | columns_info_for |
92 | /], |
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93 | ); |
94 | |
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95 | =head1 METHODS |
96 | |
97 | This class defines the following methods. |
98 | |
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99 | =head2 _build_current_replicant |
100 | |
101 | Lazy builder for the L</current_replicant_storage> attribute. |
102 | |
103 | =cut |
104 | |
105 | sub _build_current_replicant { |
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106 | my $self = shift; |
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107 | $self->next_storage; |
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108 | } |
109 | |
110 | =head2 next_storage |
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111 | |
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112 | This method should be defined in the class which consumes this role. |
113 | |
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114 | Given a pool object, return the next replicant that will serve queries. The |
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115 | default behavior is to grab the first replicant it finds but you can write |
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116 | your own subclasses of L<DBIx::Class::Storage::DBI::Replicated::Balancer> to |
117 | support other balance systems. |
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118 | |
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119 | This returns from the pool of active replicants. If there are no active |
120 | replicants, then you should have it return the master as an ultimate fallback. |
121 | |
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122 | =head2 around: next_storage |
123 | |
124 | Advice on next storage to add the autovalidation. We have this broken out so |
125 | that it's easier to break out the auto validation into a role. |
126 | |
127 | This also returns the master in the case that none of the replicants are active |
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128 | or just just for?blgot to create them :) |
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129 | |
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130 | =cut |
131 | |
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132 | my $on_master; |
133 | |
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134 | around 'next_storage' => sub { |
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135 | my ($next_storage, $self, @args) = @_; |
136 | my $now = time; |
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137 | |
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138 | ## Do we need to validate the replicants? |
139 | if( |
140 | $self->has_auto_validate_every && |
141 | ($self->auto_validate_every + $self->pool->last_validated) <= $now |
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142 | ) { |
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143 | $self->pool->validate_replicants; |
144 | } |
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145 | |
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146 | ## Get a replicant, or the master if none |
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147 | if(my $next = $self->$next_storage(@args)) { |
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148 | $self->master->debugobj->print("Moved back to slave\n") if $on_master; |
149 | $on_master = 0; |
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150 | return $next; |
151 | } else { |
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152 | $self->master->debugobj->print("No Replicants validate, falling back to master reads.\n") |
153 | unless $on_master++; |
154 | |
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155 | return $self->master; |
156 | } |
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157 | }; |
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158 | |
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159 | =head2 increment_storage |
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160 | |
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161 | Rolls the Storage to whatever is next in the queue, as defined by the Balancer. |
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162 | |
163 | =cut |
164 | |
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165 | sub increment_storage { |
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166 | my $self = shift; |
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167 | my $next_replicant = $self->next_storage; |
168 | $self->current_replicant($next_replicant); |
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169 | } |
170 | |
171 | =head2 around: select |
172 | |
173 | Advice on the select attribute. Each time we use a replicant |
174 | we need to change it via the storage pool algorithm. That way we are spreading |
175 | the load evenly (hopefully) across existing capacity. |
176 | |
177 | =cut |
178 | |
179 | around 'select' => sub { |
180 | my ($select, $self, @args) = @_; |
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181 | |
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182 | if (my $forced_pool = $args[-1]->{force_pool}) { |
183 | delete $args[-1]->{force_pool}; |
184 | return $self->_get_forced_pool($forced_pool)->select(@args); |
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185 | } elsif($self->master->{transaction_depth}) { |
186 | return $self->master->select(@args); |
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187 | } else { |
188 | $self->increment_storage; |
189 | return $self->$select(@args); |
190 | } |
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191 | }; |
192 | |
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193 | =head2 around: select_single |
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194 | |
195 | Advice on the select_single attribute. Each time we use a replicant |
196 | we need to change it via the storage pool algorithm. That way we are spreading |
197 | the load evenly (hopefully) across existing capacity. |
198 | |
199 | =cut |
200 | |
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201 | around 'select_single' => sub { |
202 | my ($select_single, $self, @args) = @_; |
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203 | |
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204 | if (my $forced_pool = $args[-1]->{force_pool}) { |
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205 | delete $args[-1]->{force_pool}; |
206 | return $self->_get_forced_pool($forced_pool)->select_single(@args); |
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207 | } elsif($self->master->{transaction_depth}) { |
208 | return $self->master->select_single(@args); |
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209 | } else { |
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210 | $self->increment_storage; |
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211 | return $self->$select_single(@args); |
212 | } |
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213 | }; |
214 | |
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215 | =head2 before: columns_info_for |
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216 | |
217 | Advice on the current_replicant_storage attribute. Each time we use a replicant |
218 | we need to change it via the storage pool algorithm. That way we are spreading |
219 | the load evenly (hopefully) across existing capacity. |
220 | |
221 | =cut |
222 | |
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223 | before 'columns_info_for' => sub { |
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224 | my $self = shift; |
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225 | $self->increment_storage; |
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226 | }; |
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227 | |
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228 | =head2 _get_forced_pool ($name) |
229 | |
230 | Given an identifier, find the most correct storage object to handle the query. |
231 | |
232 | =cut |
233 | |
234 | sub _get_forced_pool { |
235 | my ($self, $forced_pool) = @_; |
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236 | if(Scalar::Util::blessed($forced_pool)) { |
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237 | return $forced_pool; |
238 | } elsif($forced_pool eq 'master') { |
239 | return $self->master; |
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240 | } elsif(my $replicant = $self->pool->replicants->{$forced_pool}) { |
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241 | return $replicant; |
242 | } else { |
243 | $self->master->throw_exception("$forced_pool is not a named replicant."); |
244 | } |
245 | } |
246 | |
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247 | =head1 AUTHOR |
248 | |
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249 | John Napiorkowski <jjnapiork@cpan.org> |
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250 | |
251 | =head1 LICENSE |
252 | |
253 | You may distribute this code under the same terms as Perl itself. |
254 | |
255 | =cut |
256 | |
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257 | 1; |