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7fc174aada
Sometimes a controller or a job has to perform multiple independent queries, e.g.: ``` def index @posts = Post.published @categories = Category.active end ``` Since these two queries are totally independent, ideally you could execute them in parallel, so that assuming that each take 50ms, the total query time would be 50ms rather than 100ms. A very naive way to do this is to simply call `Relation#to_a` in a background thread, the problem is that most Rails applications, and even Rails itself rely on thread local state (`PerThreadRegistry`, `CurrentAttributes`, etc). So executing such a high level interface from another thread is likely to lead to many context loss problems or even thread safety issues. What we can do instead, is to schedule a much lower level operation (`Adapter#select_all`) in a thread pool, and return a future/promise. This way we kepp most of the risky code on the main thread, but perform the slow IO in background, with very little chance of executing some code that rely on state stored in thread local storage. Also since most users are on MRI, only the IO can really be parallelized, so scheduling more code to be executed in background wouldn't lead to better performance.
191 lines
5.2 KiB
Ruby
191 lines
5.2 KiB
Ruby
# frozen_string_literal: true
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#--
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# Copyright (c) 2004-2021 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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require "active_record/errors"
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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 :DelegatedType
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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 :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 :SignedId
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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 :DestroyAssociationAsyncJob
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eager_autoload do
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autoload :ConnectionAdapters
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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 :AsynchronousQueriesTracker
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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 :FutureResult
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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 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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YAML.load_tags["!ruby/object:ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MysqlString"] = "ActiveRecord::Type::String"
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