Add support schema cache dump and load.

activerecord/lib/active_record/connection_adapters/schema_cache.rb

@@ -6,21 +6,12 @@ class SchemaCache

      def initialize(conn)
        @connection = conn
        @tables     = {}

        @columns = Hash.new do |h, table_name|
          h[table_name] = conn.columns(table_name)
        end

        @columns_hash = Hash.new do |h, table_name|
          h[table_name] = Hash[columns[table_name].map { |col|
            [col.name, col]
          }]
        end

        @primary_keys = Hash.new do |h, table_name|
          h[table_name] = table_exists?(table_name) ? conn.primary_key(table_name) : nil
        end
        @columns      = {}
        @columns_hash = {}
        @primary_keys = {}
        @tables       = {}
        prepare_default_proc
      end

      # A cached lookup for table existence.
@@ -45,6 +36,35 @@ def clear_table_cache!(table_name)
        @primary_keys.delete table_name
        @tables.delete table_name
      end

      def marshal_dump
        [:@columns, :@columns_hash, :@primary_keys, :@tables].map do |val|
          self.instance_variable_get(val).inject({}) { |h, v| h[v[0]] = v[1]; h }
        end
      end

      def marshal_load(array)
        @columns, @columns_hash, @primary_keys, @tables = array
        prepare_default_proc
      end

      private

      def prepare_default_proc
        @columns.default_proc = Proc.new do |h, table_name|
          h[table_name] = connection.columns(table_name)
        end

        @columns_hash.default_proc = Proc.new do |h, table_name|
          h[table_name] = Hash[columns[table_name].map { |col|
            [col.name, col]
          }]
        end

        @primary_keys.default_proc = Proc.new do |h, table_name|
          h[table_name] = table_exists?(table_name) ? connection.primary_key(table_name) : nil
        end
      end
    end
  end
end

activerecord/test/cases/connection_adapters/schema_cache_test.rb

@@ -39,6 +39,21 @@ def test_clearing
        assert_equal 0, @cache.tables.size
        assert_equal 0, @cache.primary_keys.size
      end

      def test_dump_and_load
        @cache.columns['posts']
        @cache.columns_hash['posts']
        @cache.tables['posts']
        @cache.primary_keys['posts']

        @cache = Marshal.load(Marshal.dump(@cache))

        assert_equal 12, @cache.columns['posts'].size
        assert_equal 12, @cache.columns_hash['posts'].size
        assert @cache.tables['posts']
        assert_equal 'id', @cache.primary_keys['posts']
      end

    end
  end
end