Cache database version in schema cache

  * The database version will get cached in the schema cache file during the
    schema cache dump. When the database version check happens, the version will
    be pulled from the schema cache and thus avoid querying the database for
    the version.
  * If the schema cache file doesn't exist, we'll query the database for the
    version and cache it on the schema cache object.
  * To facilitate this change, all connection adapters now implement
    #get_database_version and #database_version. #database_version returns the
    value from the schema cache.
  * To take advantage of the cached database version, the database version check
    will now happen after the schema cache is set on the connection in the
    connection pool.

1 files changed, 14 insertions, 13 deletions

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 8ca2cfa9ed..f5da19f0f6 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -55,8 +55,8 @@ module ActiveRecord
         super(connection, logger, config)
       end
 
-      def version #:nodoc:
-        @version ||= Version.new(version_string)
+      def get_database_version #:nodoc:
+        Version.new(version_string)
       end
 
       def mariadb? # :nodoc:
@@ -68,11 +68,11 @@ module ActiveRecord
       end
 
       def supports_index_sort_order?
-        !mariadb? && version >= "8.0.1"
+        !mariadb? && database_version >= "8.0.1"
       end
 
       def supports_expression_index?
-        !mariadb? && version >= "8.0.13"
+        !mariadb? && database_version >= "8.0.13"
       end
 
       def supports_transaction_isolation?
@@ -96,16 +96,16 @@ module ActiveRecord
       end
 
       def supports_datetime_with_precision?
-        mariadb? || version >= "5.6.4"
+        mariadb? || database_version >= "5.6.4"
       end
 
       def supports_virtual_columns?
-        mariadb? || version >= "5.7.5"
+        mariadb? || database_version >= "5.7.5"
       end
 
       # See https://dev.mysql.com/doc/refman/8.0/en/optimizer-hints.html for more details.
       def supports_optimizer_hints?
-        !mariadb? && version >= "5.7.7"
+        !mariadb? && database_version >= "5.7.7"
       end
 
       def supports_advisory_locks?
@@ -526,12 +526,13 @@ module ActiveRecord
         sql
       end
 
-      private
-        def check_version
-          if version < "5.5.8"
-            raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.5.8."
-          end
+      def check_version # :nodoc:
+        if database_version < "5.5.8"
+          raise "Your version of MySQL (#{database_version}) is too old. Active Record supports MySQL >= 5.5.8."
         end
+      end
+
+      private
 
         def initialize_type_map(m = type_map)
           super
@@ -702,7 +703,7 @@ module ActiveRecord
         end
 
         def supports_rename_index?
-          mariadb? ? false : version >= "5.7.6"
+          mariadb? ? false : database_version >= "5.7.6"
         end
 
         def configure_connection