diff options
Diffstat (limited to 'activerecord/lib/active_record/middleware/database_selector/resolver.rb')
-rw-r--r-- | activerecord/lib/active_record/middleware/database_selector/resolver.rb | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/middleware/database_selector/resolver.rb b/activerecord/lib/active_record/middleware/database_selector/resolver.rb new file mode 100644 index 0000000000..a84c292714 --- /dev/null +++ b/activerecord/lib/active_record/middleware/database_selector/resolver.rb @@ -0,0 +1,90 @@ +# frozen_string_literal: true + +require "active_record/middleware/database_selector/resolver/session" + +module ActiveRecord + module Middleware + class DatabaseSelector + # The Resolver class is used by the DatabaseSelector middleware to + # determine which database the request should use. + # + # To change the behavior of the Resolver class in your application, + # create a custom resolver class that inherits from + # DatabaseSelector::Resolver and implements the methods that need to + # be changed. + # + # By default the Resolver class will send read traffic to the replica + # if it's been 2 seconds since the last write. + class Resolver # :nodoc: + SEND_TO_REPLICA_DELAY = 2.seconds + + def self.call(resolver, options = {}) + new(resolver, options) + end + + def initialize(resolver, options = {}) + @resolver = resolver + @options = options + @delay = @options && @options[:delay] ? @options[:delay] : SEND_TO_REPLICA_DELAY + @instrumenter = ActiveSupport::Notifications.instrumenter + end + + attr_reader :resolver, :delay, :instrumenter + + def read(&blk) + if read_from_primary? + read_from_primary(&blk) + else + read_from_replica(&blk) + end + end + + def write(&blk) + write_to_primary(&blk) + end + + private + + def read_from_primary(&blk) + ActiveRecord::Base.connection.while_preventing_writes do + ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do + instrumenter.instrument("database_selector.active_record.read_from_primary") do + yield + end + end + end + end + + def read_from_replica(&blk) + ActiveRecord::Base.connected_to(role: ActiveRecord::Base.reading_role) do + instrumenter.instrument("database_selector.active_record.read_from_replica") do + yield + end + end + end + + def write_to_primary(&blk) + ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do + instrumenter.instrument("database_selector.active_record.wrote_to_primary") do + yield + ensure + resolver.update_last_write_timestamp + end + end + end + + def read_from_primary? + !time_since_last_write_ok? + end + + def send_to_replica_delay + delay + end + + def time_since_last_write_ok? + Time.now - resolver.last_write_timestamp >= send_to_replica_delay + end + end + end + end +end |