diff options
Diffstat (limited to 'activerecord/lib/active_record/middleware/database_selector')
-rw-r--r-- | activerecord/lib/active_record/middleware/database_selector/resolver.rb | 90 | ||||
-rw-r--r-- | activerecord/lib/active_record/middleware/database_selector/resolver/session.rb | 45 |
2 files changed, 135 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..80b8cd7cae --- /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(context, options = {}) + new(context, options) + end + + def initialize(context, options = {}) + @context = context + @options = options + @delay = @options && @options[:delay] ? @options[:delay] : SEND_TO_REPLICA_DELAY + @instrumenter = ActiveSupport::Notifications.instrumenter + end + + attr_reader :context, :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 + context.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 - context.last_write_timestamp >= send_to_replica_delay + end + end + end + end +end diff --git a/activerecord/lib/active_record/middleware/database_selector/resolver/session.rb b/activerecord/lib/active_record/middleware/database_selector/resolver/session.rb new file mode 100644 index 0000000000..df7af054b7 --- /dev/null +++ b/activerecord/lib/active_record/middleware/database_selector/resolver/session.rb @@ -0,0 +1,45 @@ +# frozen_string_literal: true + +module ActiveRecord + module Middleware + class DatabaseSelector + class Resolver + # The session class is used by the DatabaseSelector::Resolver to save + # timestamps of the last write in the session. + # + # The last_write is used to determine whether it's safe to read + # from the replica or the request needs to be sent to the primary. + class Session # :nodoc: + def self.call(request) + new(request.session) + end + + # Converts time to a timestamp that represents milliseconds since + # epoch. + def self.convert_time_to_timestamp(time) + time.to_i * 1000 + time.usec / 1000 + end + + # Converts milliseconds since epoch timestamp into a time object. + def self.convert_timestamp_to_time(timestamp) + timestamp ? Time.at(timestamp / 1000, (timestamp % 1000) * 1000) : Time.at(0) + end + + def initialize(session) + @session = session + end + + attr_reader :session + + def last_write_timestamp + self.class.convert_timestamp_to_time(session[:last_write]) + end + + def update_last_write_timestamp + session[:last_write] = self.class.convert_time_to_timestamp(Time.now) + end + end + end + end + end +end |