Add prepared statements support for Mysql2Adapter

Gemfile

@@ -92,7 +92,7 @@ platforms :ruby, :mswin, :mswin64, :mingw, :x64_mingw do
 
   group :db do
     gem 'pg', '>= 0.18.0'
-    gem 'mysql2', '>= 0.4.0'
+    gem 'mysql2', '>= 0.4.4'
   end
 end
 

Gemfile.lock

@@ -166,9 +166,9 @@ GEM
     mono_logger (1.1.0)
     multi_json (1.11.2)
     mustache (1.0.2)
-    mysql2 (0.4.2)
-    mysql2 (0.4.2-x64-mingw32)
-    mysql2 (0.4.2-x86-mingw32)
+    mysql2 (0.4.4)
+    mysql2 (0.4.4-x64-mingw32)
+    mysql2 (0.4.4-x86-mingw32)
     nio4r (1.2.1)
     nokogiri (1.6.7.2)
       mini_portile2 (~> 2.0.0.rc2)
@@ -294,7 +294,7 @@ DEPENDENCIES
   listen (~> 3.0.5)
   minitest (< 5.3.4)
   mocha (~> 0.14)
-  mysql2 (>= 0.4.0)
+  mysql2 (>= 0.4.4)
   nokogiri (>= 1.6.7.1)
   pg (>= 0.18.0)
   psych (~> 2.0)

activerecord/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Add prepared statements support for `Mysql2Adapter`.
+
+    *Ryuta Kamizono*
+
 *   Schema dumper: Indexes are now included in the `create_table` block
     instead of listed afterward as separate `add_index` lines.
 

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -1,4 +1,5 @@
 require 'active_record/connection_adapters/abstract_adapter'
+require 'active_record/connection_adapters/statement_pool'
 require 'active_record/connection_adapters/mysql/column'
 require 'active_record/connection_adapters/mysql/explain_pretty_printer'
 require 'active_record/connection_adapters/mysql/quoting'
@@ -56,9 +57,19 @@ def arel_visitor # :nodoc:
       INDEX_TYPES  = [:fulltext, :spatial]
       INDEX_USINGS = [:btree, :hash]
 
+      class StatementPool < ConnectionAdapters::StatementPool
+        private
+
+        def dealloc(stmt)
+          stmt[:stmt].close
+        end
+      end
+
       def initialize(connection, logger, connection_options, config)
         super(connection, logger, config)
 
+        @statements = StatementPool.new(self.class.type_cast_config_to_integer(config.fetch(:statement_limit) { 1000 }))
+
         if version < '5.0.0'
           raise "Your version of MySQL (#{full_version.match(/^\d+\.\d+\.\d+/)[0]}) is too old. Active Record supports MySQL >= 5.0."
         end
@@ -93,6 +104,12 @@ def supports_bulk_alter? #:nodoc:
         true
       end
 
+      # Returns true, since this connection adapter supports prepared statement
+      # caching.
+      def supports_statement_cache?
+        true
+      end
+
       # Technically MySQL allows to create indexes with the sort order syntax
       # but at the moment (5.5) it doesn't yet implement them
       def supports_index_sort_order?
@@ -178,6 +195,14 @@ def disable_referential_integrity #:nodoc:
         end
       end
 
+      # CONNECTION MANAGEMENT ====================================
+
+      # Clears the prepared statements cache.
+      def clear_cache!
+        reload_type_map
+        @statements.clear
+      end
+
       #--
       # DATABASE STATEMENTS ======================================
       #++
@@ -191,11 +216,6 @@ def explain(arel, binds = [])
         MySQL::ExplainPrettyPrinter.new.pp(result, elapsed)
       end
 
-      def clear_cache!
-        super
-        reload_type_map
-      end
-
       # Executes the SQL statement in the context of this connection.
       def execute(sql, name = nil)
         log(sql, name) { @connection.query(sql) }

activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb

@@ -0,0 +1,125 @@
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      module DatabaseStatements
+        # Returns an ActiveRecord::Result instance.
+        def select_all(arel, name = nil, binds = [], preparable: nil)
+          result = if ExplainRegistry.collect? && prepared_statements
+            unprepared_statement { super }
+          else
+            super
+          end
+          @connection.next_result while @connection.more_results?
+          result
+        end
+
+        # Returns a record hash with the column names as keys and column values
+        # as values.
+        def select_one(arel, name = nil, binds = [])
+          arel, binds = binds_from_relation(arel, binds)
+          @connection.query_options.merge!(as: :hash)
+          select_result(to_sql(arel, binds), name, binds) do |result|
+            @connection.next_result while @connection.more_results?
+            result.first
+          end
+        ensure
+          @connection.query_options.merge!(as: :array)
+        end
+
+        # Returns an array of arrays containing the field values.
+        # Order is the same as that returned by +columns+.
+        def select_rows(sql, name = nil, binds = [])
+          select_result(sql, name, binds) do |result|
+            @connection.next_result while @connection.more_results?
+            result.to_a
+          end
+        end
+
+        # Executes the SQL statement in the context of this connection.
+        def execute(sql, name = nil)
+          if @connection
+            # make sure we carry over any changes to ActiveRecord::Base.default_timezone that have been
+            # made since we established the connection
+            @connection.query_options[:database_timezone] = ActiveRecord::Base.default_timezone
+          end
+
+          super
+        end
+
+        def exec_query(sql, name = 'SQL', binds = [], prepare: false)
+          if without_prepared_statement?(binds)
+            execute_and_free(sql, name) do |result|
+              ActiveRecord::Result.new(result.fields, result.to_a) if result
+            end
+          else
+            exec_stmt_and_free(sql, name, binds, cache_stmt: prepare) do |_, result|
+              ActiveRecord::Result.new(result.fields, result.to_a) if result
+            end
+          end
+        end
+
+        def exec_delete(sql, name, binds)
+          if without_prepared_statement?(binds)
+            execute_and_free(sql, name) { @connection.affected_rows }
+          else
+            exec_stmt_and_free(sql, name, binds) { |stmt| stmt.affected_rows }
+          end
+        end
+        alias :exec_update :exec_delete
+
+        protected
+
+        def last_inserted_id(result)
+          @connection.last_id
+        end
+
+        private
+
+        def select_result(sql, name = nil, binds = [])
+          if without_prepared_statement?(binds)
+            execute_and_free(sql, name) { |result| yield result }
+          else
+            exec_stmt_and_free(sql, name, binds, cache_stmt: true) { |_, result| yield result }
+          end
+        end
+
+        def exec_stmt_and_free(sql, name, binds, cache_stmt: false)
+          if @connection
+            # make sure we carry over any changes to ActiveRecord::Base.default_timezone that have been
+            # made since we established the connection
+            @connection.query_options[:database_timezone] = ActiveRecord::Base.default_timezone
+          end
+
+          type_casted_binds = binds.map { |attr| type_cast(attr.value_for_database) }
+
+          log(sql, name, binds) do
+            if cache_stmt
+              cache = @statements[sql] ||= {
+                stmt: @connection.prepare(sql)
+              }
+              stmt = cache[:stmt]
+            else
+              stmt = @connection.prepare(sql)
+            end
+
+            begin
+              result = stmt.execute(*type_casted_binds)
+            rescue Mysql2::Error => e
+              if cache_stmt
+                @statements.delete(sql)
+              else
+                stmt.close
+              end
+              raise e
+            end
+
+            ret = yield stmt, result
+            result.free if result
+            stmt.close unless cache_stmt
+            ret
+          end
+        end
+      end
+    end
+  end
+end

activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb

@@ -1,6 +1,7 @@
 require 'active_record/connection_adapters/abstract_mysql_adapter'
+require 'active_record/connection_adapters/mysql/database_statements'
 
-gem 'mysql2', '>= 0.3.18', '< 0.5'
+gem 'mysql2', '~> 0.4.4'
 require 'mysql2'
 
 module ActiveRecord
@@ -35,9 +36,11 @@ module ConnectionAdapters
     class Mysql2Adapter < AbstractMysqlAdapter
       ADAPTER_NAME = 'Mysql2'.freeze
 
+      include MySQL::DatabaseStatements
+
       def initialize(connection, logger, connection_options, config)
         super
-        @prepared_statements = false
+        @prepared_statements = false unless config.key?(:prepared_statements)
         configure_connection
       end
 
@@ -103,55 +106,6 @@ def disconnect!
         end
       end
 
-      #--
-      # DATABASE STATEMENTS ======================================
-      #++
-
-      # Returns a record hash with the column names as keys and column values
-      # as values.
-      def select_one(arel, name = nil, binds = [])
-        arel, binds = binds_from_relation(arel, binds)
-        execute(to_sql(arel, binds), name).each(as: :hash) do |row|
-          @connection.next_result while @connection.more_results?
-          return row
-        end
-      end
-
-      # Returns an array of arrays containing the field values.
-      # Order is the same as that returned by +columns+.
-      def select_rows(sql, name = nil, binds = [])
-        result = execute(sql, name)
-        @connection.next_result while @connection.more_results?
-        result.to_a
-      end
-
-      # Executes the SQL statement in the context of this connection.
-      def execute(sql, name = nil)
-        if @connection
-          # make sure we carry over any changes to ActiveRecord::Base.default_timezone that have been
-          # made since we established the connection
-          @connection.query_options[:database_timezone] = ActiveRecord::Base.default_timezone
-        end
-
-        super
-      end
-
-      def exec_query(sql, name = 'SQL', binds = [], prepare: false)
-        result = execute(sql, name)
-        @connection.next_result while @connection.more_results?
-        ActiveRecord::Result.new(result.fields, result.to_a) if result
-      end
-
-      def exec_delete(sql, name, binds)
-        execute to_sql(sql, binds), name
-        @connection.affected_rows
-      end
-      alias :exec_update :exec_delete
-
-      def last_inserted_id(result)
-        @connection.last_id
-      end
-
       private
 
       def connect