Ruby-Mysql2のエンコーディングutf8mb4によるインデックス作成の問題（パフォーマンスに影響を及ぼす）

Question

私のテーブルに複合インデックスを作成しようとしています。下の表は私にパフォーマンス上の問題があり、ut8mb4の文字エンコーディングを持っています。私はこのフォーラムでは、次のポストを経た

== 20161103114941 AddIndexOnKeyAndIdOnInvitees: migrating - Shard: master ===== 
-- add_index(:invitees, [:key, :created_at]) 
rake aborted! 
StandardError: An error has occurred, all later migrations canceled: 

Mysql2::Error: Specified key was too long; max key length is 767 bytes: CREATE INDEX `index_invitees_on_key_and_created_at` ON `invitees` (`key`, `created_at`) 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:299:in `query' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:299:in `block in execute' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_adapter.rb:473:in `block in log' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activesupport-4.2.1/lib/active_support/notifications/instrumenter.rb:20:in `instrument' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/abstract_adapter.rb:15:in `instrument' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_adapter.rb:467:in `log' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:299:in `execute' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/mysql2_adapter.rb:231:in `execute' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:529:in `add_index' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:662:in `block in method_missing' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:632:in `block in say_with_time' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:632:in `say_with_time' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:652:in `method_missing' 
/var/www/production_hobnob_copy/db/migrate/20161103114941_add_index_on_key_and_id_on_invitees.rb:3:in `change' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:606:in `exec_migration' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:590:in `block (2 levels) in migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:589:in `block in migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:588:in `migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:765:in `migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:995:in `block in execute_migration_in_transaction' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:1043:in `ddl_transaction' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:994:in `execute_migration_in_transaction' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:956:in `block in migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:952:in `each' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:952:in `migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/migration.rb:86:in `migrate_with_octopus' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:820:in `up' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/migration.rb:113:in `block in up_with_octopus' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:246:in `block (2 levels) in run_queries_on_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:509:in `using_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:245:in `block in run_queries_on_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:492:in `keeping_connection_proxy' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:244:in `run_queries_on_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:253:in `block in send_queries_to_multiple_shards' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:252:in `map' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:252:in `send_queries_to_multiple_shards' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/migration.rb:112:in `up_with_octopus' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/migration.rb:798:in `migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/migration.rb:104:in `block in migrate_with_octopus' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:246:in `block (2 levels) in run_queries_on_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:509:in `using_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:245:in `block in run_queries_on_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:492:in `keeping_connection_proxy' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:244:in `run_queries_on_shard' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:253:in `block in send_queries_to_multiple_shards' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:252:in `map' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/proxy.rb:252:in `send_queries_to_multiple_shards' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/ar-octopus-0.8.6/lib/octopus/migration.rb:103:in `migrate_with_octopus' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/tasks/database_tasks.rb:137:in `migrate' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/gems/activerecord-4.2.1/lib/active_record/railties/databases.rake:44:in `block (2 levels) in <top (required)>' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/bin/ruby_executable_hooks:15:in `eval' 
/home/ubuntu/.rvm/gems/ruby-2.0.0-p648/bin/ruby_executable_hooks:15:in `<main>' 
Tasks: TOP => db:migrate 

： - - ：下のエラー以下

Mysql2::Error: Specified key was too long 

全体の誤差が与えられている

Rails creating schema_migrations - Mysql2::Error: Specified key was too long

と解決策は、私の場合は不可能な文字エンコーディングをutf8に変換することです。これのための回避策はありますか？

任意の提案やヘルプは非常に参考になります。..

おかげでたくさんの古いバージョンでは

Answer 1

は、インデックスが767バイトに制限されていました。これは普及していたVARCHAR(255) CHARACTER SET utf8のための十分な部屋でした。

VARCHAR(255) CHARACTER SET utf8mb4以上が必要です。新しいバージョンでは制限値が引き上げられているので、動作します。

ソリューション：

• アップグレードmysqlの。
• 255を減らしてください - あなたのデータを見て、余計な255ではなく、賢明な数字を使用してください。それが191未満であれば、インデックスが機能します。

手順（5.7.7以降では必要ありません）

SET GLOBAL innodb_file_format=Barracuda; 
SET GLOBAL innodb_file_per_table=1; 
SET GLOBAL innodb_large_prefix=1; 
logout & login (to get the global values); 
ALTER TABLE tbl ROW_FORMAT=DYNAMIC; 

その後、多分あなたは、インデックス（255をすることができます5.6.3/5.5.14（またはそれ以降）を取得し、... ）utf8mb4。

「キーが長すぎます」というのは、インデックスを追加できないという点で間接的に「パフォーマンス」に影響します。