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.

8 files changed, 34 insertions, 11 deletions

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