From 8297f8a31e88468106b013219104df17659ab718 Mon Sep 17 00:00:00 2001
From: Ryuta Kamizono <kamipo@gmail.com>
Date: Tue, 15 Oct 2019 08:44:16 +0900
Subject: [PATCH] Merge pull request #37465 from
 alpaca-tc/optimize_primary_keys

Fixed performance regression introduced MySQL 8.0
---
 activerecord/CHANGELOG.md                                   | 4 ++++
 .../connection_adapters/abstract_mysql_adapter.rb           | 6 +++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index a8d5fd1427..c508fc65fd 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Fixed the performance regression for `primary_keys` introduced MySQL 8.0.
+
+    *Hiroyuki Ishii*
+
 *   `insert`, `insert_all`, `upsert`, and `upsert_all` now clear the query cache.
 
     *Eugene Kenny*
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index afbe7384ef..f68df40a87 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -440,11 +440,11 @@ def primary_keys(table_name) # :nodoc:
 
         query_values(<<~SQL, "SCHEMA")
           SELECT column_name
-          FROM information_schema.key_column_usage
-          WHERE constraint_name = 'PRIMARY'
+          FROM information_schema.statistics
+          WHERE index_name = 'PRIMARY'
             AND table_schema = #{scope[:schema]}
             AND table_name = #{scope[:name]}
-          ORDER BY ordinal_position
+          ORDER BY seq_in_index
         SQL
       end
 
-- 
GitLab