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0abcec416b
The following PR adds behavior to Rails to allow an application to automatically switch it's connection from the primary to the replica. A request will be sent to the replica if: * The request is a read request (`GET` or `HEAD`) * AND It's been 2 seconds since the last write to the database (because we don't want to send a user to a replica if the write hasn't made it to the replica yet) A request will be sent to the primary if: * It's not a GET/HEAD request (ie is a POST, PATCH, etc) * Has been less than 2 seconds since the last write to the database The implementation that decides when to switch reads (the 2 seconds) is "safe" to use in production but not recommended without adequate testing with your infrastructure. At GitHub in addition to the a 5 second delay we have a curcuit breaker that checks the replication delay and will send the query to a replica before the 5 seconds has passed. This is specific to our application and therefore not something Rails should be doing for you. You'll need to test and implement more robust handling of when to switch based on your infrastructure. The auto switcher in Rails is meant to be a basic implementation / API that acts as a guide for how to implement autoswitching. The impementation here is meant to be strict enough that you know how to implement your own resolver and operations classes but flexible enough that we're not telling you how to do it. The middleware is not included automatically and can be installed in your application with the classes you want to use for the resolver and operations passed in. If you don't pass any classes into the middleware the Rails default Resolver and Session classes will be used. The Resolver decides what parameters define when to switch, Operations sets timestamps for the Resolver to read from. For example you may want to use cookies instead of a session so you'd implement a Resolver::Cookies class and pass that into the middleware via configuration options. ``` config.active_record.database_selector = { delay: 2.seconds } config.active_record.database_resolver = MyResolver config.active_record.database_operations = MyResolver::MyCookies ``` Your classes can inherit from the existing classes and reimplment the methods (or implement more methods) that you need to do the switching. You only need to implement methods that you want to change. For example if you wanted to set the session token for the last read from a replica you would reimplement the `read_from_replica` method in your resolver class and implement a method that updates a new timestamp in your operations class.
196 lines
5.3 KiB
Ruby
196 lines
5.3 KiB
Ruby
# frozen_string_literal: true
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#--
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# Copyright (c) 2004-2019 David Heinemeier Hansson
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#
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# Permission is hereby granted, free of charge, to any person obtaining
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# a copy of this software and associated documentation files (the
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# "Software"), to deal in the Software without restriction, including
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# without limitation the rights to use, copy, modify, merge, publish,
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# distribute, sublicense, and/or sell copies of the Software, and to
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# permit persons to whom the Software is furnished to do so, subject to
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# the following conditions:
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#
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# The above copyright notice and this permission notice shall be
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# included in all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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#++
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require "active_support"
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require "active_support/rails"
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require "active_model"
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require "arel"
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require "yaml"
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require "active_record/version"
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require "active_model/attribute_set"
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module ActiveRecord
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extend ActiveSupport::Autoload
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autoload :Base
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autoload :Callbacks
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autoload :Core
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autoload :ConnectionHandling
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autoload :CounterCache
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autoload :DynamicMatchers
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autoload :Enum
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autoload :InternalMetadata
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autoload :Explain
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autoload :Inheritance
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autoload :Integration
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autoload :Migration
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autoload :Migrator, "active_record/migration"
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autoload :ModelSchema
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autoload :NestedAttributes
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autoload :NoTouching
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autoload :TouchLater
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autoload :Persistence
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autoload :QueryCache
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autoload :Querying
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autoload :CollectionCacheKey
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autoload :ReadonlyAttributes
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autoload :RecordInvalid, "active_record/validations"
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autoload :Reflection
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autoload :RuntimeRegistry
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autoload :Sanitization
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autoload :Schema
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autoload :SchemaDumper
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autoload :SchemaMigration
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autoload :Scoping
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autoload :Serialization
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autoload :StatementCache
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autoload :Store
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autoload :Suppressor
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autoload :Timestamp
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autoload :Transactions
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autoload :Translation
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autoload :Validations
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autoload :SecureToken
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autoload :DatabaseSelector, "active_record/middleware/database_selector"
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eager_autoload do
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autoload :ActiveRecordError, "active_record/errors"
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autoload :ConnectionNotEstablished, "active_record/errors"
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autoload :ConnectionAdapters, "active_record/connection_adapters/abstract_adapter"
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autoload :Aggregations
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autoload :Associations
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autoload :AttributeAssignment
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autoload :AttributeMethods
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autoload :AutosaveAssociation
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autoload :LegacyYamlAdapter
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autoload :Relation
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autoload :AssociationRelation
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autoload :NullRelation
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autoload_under "relation" do
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autoload :QueryMethods
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autoload :FinderMethods
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autoload :Calculations
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autoload :PredicateBuilder
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autoload :SpawnMethods
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autoload :Batches
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autoload :Delegation
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end
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autoload :Result
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autoload :TableMetadata
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autoload :Type
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end
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module Coders
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autoload :YAMLColumn, "active_record/coders/yaml_column"
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autoload :JSON, "active_record/coders/json"
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end
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module AttributeMethods
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extend ActiveSupport::Autoload
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eager_autoload do
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autoload :BeforeTypeCast
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autoload :Dirty
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autoload :PrimaryKey
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autoload :Query
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autoload :Read
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autoload :TimeZoneConversion
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autoload :Write
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autoload :Serialization
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end
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end
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module Locking
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extend ActiveSupport::Autoload
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eager_autoload do
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autoload :Optimistic
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autoload :Pessimistic
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end
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end
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module ConnectionAdapters
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extend ActiveSupport::Autoload
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eager_autoload do
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autoload :AbstractAdapter
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end
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end
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module Scoping
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extend ActiveSupport::Autoload
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eager_autoload do
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autoload :Named
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autoload :Default
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end
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end
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module Middleware
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extend ActiveSupport::Autoload
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autoload :DatabaseSelector, "active_record/middleware/database_selector"
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end
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module Tasks
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extend ActiveSupport::Autoload
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autoload :DatabaseTasks
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autoload :SQLiteDatabaseTasks, "active_record/tasks/sqlite_database_tasks"
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autoload :MySQLDatabaseTasks, "active_record/tasks/mysql_database_tasks"
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autoload :PostgreSQLDatabaseTasks,
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"active_record/tasks/postgresql_database_tasks"
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end
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autoload :TestDatabases, "active_record/test_databases"
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autoload :TestFixtures, "active_record/fixtures"
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def self.eager_load!
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super
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ActiveRecord::Locking.eager_load!
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ActiveRecord::Scoping.eager_load!
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ActiveRecord::Associations.eager_load!
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ActiveRecord::AttributeMethods.eager_load!
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ActiveRecord::ConnectionAdapters.eager_load!
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end
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end
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ActiveSupport.on_load(:active_record) do
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Arel::Table.engine = self
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end
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ActiveSupport.on_load(:i18n) do
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I18n.load_path << File.expand_path("active_record/locale/en.yml", __dir__)
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end
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YAML.load_tags["!ruby/object:ActiveRecord::AttributeSet"] = "ActiveModel::AttributeSet"
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YAML.load_tags["!ruby/object:ActiveRecord::Attribute::FromDatabase"] = "ActiveModel::Attribute::FromDatabase"
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YAML.load_tags["!ruby/object:ActiveRecord::LazyAttributeHash"] = "ActiveModel::LazyAttributeHash"
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