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.

18 files changed, 106 insertions, 67 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 0ded1a5318..68498b5dc5 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -810,6 +810,7 @@ module ActiveRecord
         def new_connection
           Base.send(spec.adapter_method, spec.config).tap do |conn|
             conn.schema_cache = schema_cache.dup if schema_cache
+            conn.check_version
           end
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 7aad306d50..200184c2f9 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -133,8 +133,6 @@ module ActiveRecord
         @advisory_locks_enabled = self.class.type_cast_config_to_boolean(
           config.fetch(:advisory_locks, true)
         )
-
-        check_version
       end
 
       def replica?
@@ -575,9 +573,17 @@ module ActiveRecord
         "INSERT #{insert.into} #{insert.values_list}"
       end
 
+      def get_database_version # :nodoc:
+      end
+
+      def database_version # :nodoc:
+        schema_cache.database_version
+      end
+
+      def check_version # :nodoc:
+      end
+
       private
-        def check_version
-        end
 
         def type_map
           @type_map ||= Type::TypeMap.new.tap do |mapping|
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
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
index 57518b02fa..a37557361a 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
@@ -64,7 +64,7 @@ module ActiveRecord
           end
 
           def extract_expression_for_virtual_column(column)
-            if @connection.mariadb? && @connection.version < "10.2.5"
+            if @connection.mariadb? && @connection.database_version < "10.2.5"
               create_table_info = @connection.send(:create_table_info, column.table_name)
               column_name = @connection.quote_column_name(column.name)
               if %r/#{column_name} #{Regexp.quote(column.sql_type)}(?: COLLATE \w+)? AS \((?<expression>.+?)\) #{column.extra}/ =~ create_table_info
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
index 4018f0815c..a1f90a0642 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -126,9 +126,9 @@ module ActiveRecord
 
           def row_format_dynamic_by_default?
             if mariadb?
-              version >= "10.2.2"
+              database_version >= "10.2.2"
             else
-              version >= "5.7.9"
+              database_version >= "5.7.9"
             end
           end
 
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index 9bdaa00336..0dc880c731 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -43,7 +43,7 @@ module ActiveRecord
       end
 
       def supports_json?
-        !mariadb? && version >= "5.7.8"
+        !mariadb? && database_version >= "5.7.8"
       end
 
       def supports_comments?
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index a38c1325c0..41d1a8e4ab 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -287,7 +287,7 @@ module ActiveRecord
             quoted_sequence = quote_table_name(sequence)
             max_pk = query_value("SELECT MAX(#{quote_column_name pk}) FROM #{quote_table_name(table)}", "SCHEMA")
             if max_pk.nil?
-              if postgresql_version >= 100000
+              if database_version >= 100000
                 minvalue = query_value("SELECT seqmin FROM pg_sequence WHERE seqrelid = #{quote(quoted_sequence)}::regclass", "SCHEMA")
               else
                 minvalue = query_value("SELECT min_value FROM #{quoted_sequence}", "SCHEMA")
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 29f764e8f4..0ed4e61d18 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -201,7 +201,7 @@ module ActiveRecord
       end
 
       def supports_insert_on_conflict?
-        postgresql_version >= 90500
+        database_version >= 90500
       end
       alias supports_insert_on_duplicate_skip? supports_insert_on_conflict?
       alias supports_insert_on_duplicate_update? supports_insert_on_conflict?
@@ -344,7 +344,7 @@ module ActiveRecord
       end
 
       def supports_pgcrypto_uuid?
-        postgresql_version >= 90400
+        database_version >= 90400
       end
 
       def supports_optimizer_hints?
@@ -424,7 +424,7 @@ module ActiveRecord
       }
 
       # Returns the version of the connected PostgreSQL server.
-      def postgresql_version
+      def get_database_version
         @connection.server_version
       end
 
@@ -446,12 +446,13 @@ module ActiveRecord
         sql
       end
 
-      private
-        def check_version
-          if postgresql_version < 90300
-            raise "Your version of PostgreSQL (#{postgresql_version}) is too old. Active Record supports PostgreSQL >= 9.3."
-          end
+      def check_version # :nodoc:
+        if database_version < 90300
+          raise "Your version of PostgreSQL (#{database_version}) is too old. Active Record supports PostgreSQL >= 9.3."
         end
+      end
+
+      private
 
         # See https://www.postgresql.org/docs/current/static/errcodes-appendix.html
         VALUE_LIMIT_VIOLATION = "22001"
diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
index 07453b4403..dbfe1e4a34 100644
--- a/activerecord/lib/active_record/connection_adapters/schema_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -26,21 +26,23 @@ module ActiveRecord
       end
 
       def encode_with(coder)
-        coder["columns"]      = @columns
-        coder["columns_hash"] = @columns_hash
-        coder["primary_keys"] = @primary_keys
-        coder["data_sources"] = @data_sources
-        coder["indexes"]      = @indexes
-        coder["version"]      = connection.migration_context.current_version
+        coder["columns"]          = @columns
+        coder["columns_hash"]     = @columns_hash
+        coder["primary_keys"]     = @primary_keys
+        coder["data_sources"]     = @data_sources
+        coder["indexes"]          = @indexes
+        coder["version"]          = connection.migration_context.current_version
+        coder["database_version"] = database_version
       end
 
       def init_with(coder)
-        @columns      = coder["columns"]
-        @columns_hash = coder["columns_hash"]
-        @primary_keys = coder["primary_keys"]
-        @data_sources = coder["data_sources"]
-        @indexes      = coder["indexes"] || {}
-        @version      = coder["version"]
+        @columns          = coder["columns"]
+        @columns_hash     = coder["columns_hash"]
+        @primary_keys     = coder["primary_keys"]
+        @data_sources     = coder["data_sources"]
+        @indexes          = coder["indexes"] || {}
+        @version          = coder["version"]
+        @database_version = coder["database_version"]
       end
 
       def primary_keys(table_name)
@@ -91,6 +93,10 @@ module ActiveRecord
         @indexes[table_name] ||= connection.indexes(table_name)
       end
 
+      def database_version # :nodoc:
+        @database_version ||= connection.get_database_version
+      end
+
       # Clears out internal caches
       def clear!
         @columns.clear
@@ -99,6 +105,7 @@ module ActiveRecord
         @data_sources.clear
         @indexes.clear
         @version = nil
+        @database_version = nil
       end
 
       def size
@@ -117,11 +124,11 @@ module ActiveRecord
       def marshal_dump
         # if we get current version during initialization, it happens stack over flow.
         @version = connection.migration_context.current_version
-        [@version, @columns, @columns_hash, @primary_keys, @data_sources, @indexes]
+        [@version, @columns, @columns_hash, @primary_keys, @data_sources, @indexes, database_version]
       end
 
       def marshal_load(array)
-        @version, @columns, @columns_hash, @primary_keys, @data_sources, @indexes = array
+        @version, @columns, @columns_hash, @primary_keys, @data_sources, @indexes, @database_version = array
         @indexes = @indexes || {}
       end
 
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index ff23a525b9..8504438d2d 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -111,7 +111,7 @@ module ActiveRecord
       end
 
       def supports_expression_index?
-        sqlite_version >= "3.9.0"
+        database_version >= "3.9.0"
       end
 
       def requires_reloading?
@@ -135,7 +135,7 @@ module ActiveRecord
       end
 
       def supports_insert_on_conflict?
-        sqlite_version >= "3.24.0"
+        database_version >= "3.24.0"
       end
       alias supports_insert_on_duplicate_skip? supports_insert_on_conflict?
       alias supports_insert_on_duplicate_update? supports_insert_on_conflict?
@@ -397,6 +397,16 @@ module ActiveRecord
         sql
       end
 
+      def get_database_version # :nodoc:
+        SQLite3Adapter::Version.new(query_value("SELECT sqlite_version(*)"))
+      end
+
+      def check_version # :nodoc:
+        if database_version < "3.8.0"
+          raise "Your version of SQLite (#{database_version}) is too old. Active Record supports SQLite >= 3.8."
+        end
+      end
+
       private
         # See https://www.sqlite.org/limits.html,
         # the default value is 999 when not configured.
@@ -404,12 +414,6 @@ module ActiveRecord
           999
         end
 
-        def check_version
-          if sqlite_version < "3.8.0"
-            raise "Your version of SQLite (#{sqlite_version}) is too old. Active Record supports SQLite >= 3.8."
-          end
-        end
-
         def initialize_type_map(m = type_map)
           super
           register_class_with_limit m, %r(int)i, SQLite3Integer
@@ -527,10 +531,6 @@ module ActiveRecord
                      SELECT #{quoted_from_columns} FROM #{quote_table_name(from)}")
         end
 
-        def sqlite_version
-          @sqlite_version ||= SQLite3Adapter::Version.new(query_value("SELECT sqlite_version(*)"))
-        end
-
         def translate_exception(exception, message:, sql:, binds:)
           case exception.message
           # SQLite 3.8.2 returns a newly formatted error message:
diff --git a/activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb b/activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb
index 00a075e063..cbe55f1d53 100644
--- a/activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb
@@ -46,10 +46,7 @@ class Mysql2DatetimePrecisionQuotingTest < ActiveRecord::Mysql2TestCase
 
     def stub_version(full_version_string)
       @connection.stub(:full_version, full_version_string) do
-        @connection.remove_instance_variable(:@version) if @connection.instance_variable_defined?(:@version)
         yield
       end
-    ensure
-      @connection.remove_instance_variable(:@version) if @connection.instance_variable_defined?(:@version)
     end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/sp_test.rb b/activerecord/test/cases/adapters/mysql2/sp_test.rb
index 7b6dce71e9..626ef59570 100644
--- a/activerecord/test/cases/adapters/mysql2/sp_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/sp_test.rb
@@ -9,7 +9,7 @@ class Mysql2StoredProcedureTest < ActiveRecord::Mysql2TestCase
 
   def setup
     @connection = ActiveRecord::Base.connection
-    unless ActiveRecord::Base.connection.version >= "5.6.0"
+    unless ActiveRecord::Base.connection.database_version >= "5.6.0"
       skip("no stored procedure support")
     end
   end
diff --git a/activerecord/test/cases/adapters/postgresql/geometric_test.rb b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
index 8c6f046553..14c262f4ce 100644
--- a/activerecord/test/cases/adapters/postgresql/geometric_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
@@ -247,7 +247,7 @@ class PostgreSQLGeometricLineTest < ActiveRecord::PostgreSQLTestCase
   class PostgresqlLine < ActiveRecord::Base; end
 
   setup do
-    unless ActiveRecord::Base.connection.send(:postgresql_version) >= 90400
+    unless ActiveRecord::Base.connection.database_version >= 90400
       skip("line type is not fully implemented")
     end
     @connection = ActiveRecord::Base.connection
diff --git a/activerecord/test/cases/adapters/postgresql/partitions_test.rb b/activerecord/test/cases/adapters/postgresql/partitions_test.rb
index 0ac9ca1200..4015bc94f9 100644
--- a/activerecord/test/cases/adapters/postgresql/partitions_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/partitions_test.rb
@@ -12,7 +12,7 @@ class PostgreSQLPartitionsTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_partitions_table_exists
-    skip unless ActiveRecord::Base.connection.postgresql_version >= 100000
+    skip unless ActiveRecord::Base.connection.database_version >= 100000
     @connection.create_table :partitioned_events, force: true, id: false,
       options: "partition by range (issued_at)" do |t|
       t.timestamp :issued_at
diff --git a/activerecord/test/cases/connection_adapters/schema_cache_test.rb b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
index 5113548091..89a9c30f9b 100644
--- a/activerecord/test/cases/connection_adapters/schema_cache_test.rb
+++ b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
@@ -6,8 +6,9 @@ module ActiveRecord
   module ConnectionAdapters
     class SchemaCacheTest < ActiveRecord::TestCase
       def setup
-        @connection = ActiveRecord::Base.connection
-        @cache      = SchemaCache.new @connection
+        @connection       = ActiveRecord::Base.connection
+        @cache            = SchemaCache.new @connection
+        @database_version = @connection.get_database_version
       end
 
       def test_primary_key
@@ -28,6 +29,7 @@ module ActiveRecord
           assert new_cache.data_sources("posts")
           assert_equal "id", new_cache.primary_keys("posts")
           assert_equal 1, new_cache.indexes("posts").size
+          assert_equal @database_version.to_s, new_cache.database_version.to_s
         end
       end
 
@@ -55,6 +57,20 @@ module ActiveRecord
         @connection.schema_cache = old_cache
       end
 
+      def test_yaml_loads_5_1_dump_without_database_version_still_queries_for_database_version
+        @cache = YAML.load(File.read(schema_dump_path))
+
+        # Simulate assignment in railtie after loading the cache.
+        old_cache, @connection.schema_cache = @connection.schema_cache, @cache
+
+        # We can't verify queries get executed because the database version gets
+        # cached in both MySQL and PostgreSQL outside of the schema cache.
+        assert_nil @cache.instance_variable_get(:@database_version)
+        assert_equal @database_version.to_s, @cache.database_version.to_s
+      ensure
+        @connection.schema_cache = old_cache
+      end
+
       def test_primary_key_for_non_existent_table
         assert_nil @cache.primary_keys("omgponies")
       end
@@ -74,6 +90,14 @@ module ActiveRecord
         assert_equal indexes, @cache.indexes("posts")
       end
 
+      def test_caches_database_version
+        @cache.database_version # cache database_version
+
+        assert_no_queries do
+          assert_equal @database_version.to_s, @cache.database_version.to_s
+        end
+      end
+
       def test_clearing
         @cache.columns("posts")
         @cache.columns_hash("posts")
@@ -84,6 +108,7 @@ module ActiveRecord
         @cache.clear!
 
         assert_equal 0, @cache.size
+        assert_nil @cache.instance_variable_get(:@database_version)
       end
 
       def test_dump_and_load
@@ -101,6 +126,7 @@ module ActiveRecord
           assert @cache.data_sources("posts")
           assert_equal "id", @cache.primary_keys("posts")
           assert_equal 1, @cache.indexes("posts").size
+          assert_equal @database_version.to_s, @cache.database_version.to_s
         end
       end
 
diff --git a/activerecord/test/cases/defaults_test.rb b/activerecord/test/cases/defaults_test.rb
index 5d02e59ef6..50a86b0a19 100644
--- a/activerecord/test/cases/defaults_test.rb
+++ b/activerecord/test/cases/defaults_test.rb
@@ -89,7 +89,7 @@ if current_adapter?(:PostgreSQLAdapter)
 
     test "schema dump includes default expression" do
       output = dump_table_schema("defaults")
-      if ActiveRecord::Base.connection.postgresql_version >= 100000
+      if ActiveRecord::Base.connection.database_version >= 100000
         assert_match %r/t\.date\s+"modified_date",\s+default: -> { "CURRENT_DATE" }/, output
         assert_match %r/t\.datetime\s+"modified_time",\s+default: -> { "CURRENT_TIMESTAMP" }/, output
       else
diff --git a/activerecord/test/cases/helper.rb b/activerecord/test/cases/helper.rb
index f95d082907..298ee40df1 100644
--- a/activerecord/test/cases/helper.rb
+++ b/activerecord/test/cases/helper.rb
@@ -53,7 +53,7 @@ def supports_default_expression?
     true
   elsif current_adapter?(:Mysql2Adapter)
     conn = ActiveRecord::Base.connection
-    !conn.mariadb? && conn.version >= "8.0.13"
+    !conn.mariadb? && conn.database_version >= "8.0.13"
   end
 end
 
diff --git a/activerecord/test/cases/migration/columns_test.rb b/activerecord/test/cases/migration/columns_test.rb
index dbbba9c5fa..cce3461e18 100644
--- a/activerecord/test/cases/migration/columns_test.rb
+++ b/activerecord/test/cases/migration/columns_test.rb
@@ -136,7 +136,7 @@ module ActiveRecord
       def test_remove_column_with_multi_column_index
         # MariaDB starting with 10.2.8
         # Dropping a column that is part of a multi-column UNIQUE constraint is not permitted.
-        skip if current_adapter?(:Mysql2Adapter) && connection.mariadb? && connection.version >= "10.2.8"
+        skip if current_adapter?(:Mysql2Adapter) && connection.mariadb? && connection.database_version >= "10.2.8"
 
         add_column "test_models", :hat_size, :integer
         add_column "test_models", :hat_style, :string, limit: 100