Merge pull request rails#33835 from schneems/schneems/faster_cache_version

Use raw time string from DB to generate ActiveRecord#cache_version

Author: sgrif

activerecord/lib/active_record/integration.rb

@@ -96,8 +96,19 @@ def cache_key(*timestamp_names)
     # Note, this method will return nil if ActiveRecord::Base.cache_versioning is set to
     # +false+ (which it is by default until Rails 6.0).
     def cache_version
-      if cache_versioning && timestamp = try(:updated_at)
-        timestamp.utc.to_s(:usec)
+      return unless cache_versioning
+
+      if has_attribute?("updated_at")
+        timestamp = updated_at_before_type_cast
+        if can_use_fast_cache_version?(timestamp)
+          raw_timestamp_to_cache_version(timestamp)
+        elsif timestamp = updated_at
+          timestamp.utc.to_s(cache_timestamp_format)
+        end
+      else
+        if self.class.has_attribute?("updated_at")
+          raise ActiveModel::MissingAttributeError, "missing attribute: updated_at"
+        end
       end
     end
 
@@ -151,5 +162,42 @@ def to_param(method_name = nil)
         end
       end
     end
+
+    private
+      # Detects if the value before type cast
+      # can be used to generate a cache_version.
+      #
+      # The fast cache version only works with a
+      # string value directly from the database.
+      #
+      # We also must check if the timestamp format has been changed
+      # or if the timezone is not set to UTC then
+      # we cannot apply our transformations correctly.
+      def can_use_fast_cache_version?(timestamp)
+        timestamp.is_a?(String) &&
+          cache_timestamp_format == :usec &&
+          default_timezone == :utc &&
+          !updated_at_came_from_user?
+      end
+
+      # Converts a raw database string to `:usec`
+      # format.
+      #
+      # Example:
+      #
+      #   timestamp = "2018-10-15 20:02:15.266505"
+      #   raw_timestamp_to_cache_version(timestamp)
+      #   # => "20181015200215266505"
+      #
+      # Postgres truncates trailing zeros, https://bit.ly/2QUlXiZ
+      # to account for this we pad the output with zeros
+      def raw_timestamp_to_cache_version(timestamp)
+        key = timestamp.delete("- :.")
+        if key.length < 20
+          key.ljust(20, "0")
+        else
+          key
+        end
+      end
   end
 end

activerecord/test/cases/cache_key_test.rb

@@ -44,10 +44,88 @@ class CacheMeWithVersion < ActiveRecord::Base
 
     test "cache_key_with_version always has both key and version" do
       r1 = CacheMeWithVersion.create
-      assert_equal "active_record/cache_key_test/cache_me_with_versions/#{r1.id}-#{r1.updated_at.to_s(:usec)}", r1.cache_key_with_version
+      assert_equal "active_record/cache_key_test/cache_me_with_versions/#{r1.id}-#{r1.updated_at.utc.to_s(:usec)}", r1.cache_key_with_version
 
       r2 = CacheMe.create
-      assert_equal "active_record/cache_key_test/cache_mes/#{r2.id}-#{r2.updated_at.to_s(:usec)}", r2.cache_key_with_version
+      assert_equal "active_record/cache_key_test/cache_mes/#{r2.id}-#{r2.updated_at.utc.to_s(:usec)}", r2.cache_key_with_version
+    end
+
+    test "cache_version is the same when it comes from the DB or from the user" do
+      skip("Mysql2 does not return a string value for updated_at") if current_adapter?(:Mysql2Adapter)
+
+      record = CacheMeWithVersion.create
+      record_from_db = CacheMeWithVersion.find(record.id)
+      assert_not_called(record_from_db, :updated_at) do
+        record_from_db.cache_version
+      end
+
+      assert_equal record.cache_version, record_from_db.cache_version
+    end
+
+    test "cache_version does not truncate zeros when timestamp ends in zeros" do
+      skip("Mysql2 does not return a string value for updated_at") if current_adapter?(:Mysql2Adapter)
+
+      travel_to Time.now.beginning_of_day do
+        record = CacheMeWithVersion.create
+        record_from_db = CacheMeWithVersion.find(record.id)
+        assert_not_called(record_from_db, :updated_at) do
+          record_from_db.cache_version
+        end
+
+        assert_equal record.cache_version, record_from_db.cache_version
+      end
+    end
+
+    test "cache_version calls updated_at when the value is generated at create time" do
+      record = CacheMeWithVersion.create
+      assert_called(record, :updated_at) do
+        record.cache_version
+      end
+    end
+
+    test "cache_version does NOT call updated_at when value is from the database" do
+      skip("Mysql2 does not return a string value for updated_at") if current_adapter?(:Mysql2Adapter)
+
+      record = CacheMeWithVersion.create
+      record_from_db = CacheMeWithVersion.find(record.id)
+      assert_not_called(record_from_db, :updated_at) do
+        record_from_db.cache_version
+      end
+    end
+
+    test "cache_version does call updated_at when it is assigned via a Time object" do
+      record = CacheMeWithVersion.create
+      record_from_db = CacheMeWithVersion.find(record.id)
+      assert_called(record_from_db, :updated_at) do
+        record_from_db.updated_at = Time.now
+        record_from_db.cache_version
+      end
+    end
+
+    test "cache_version does call updated_at when it is assigned via a string" do
+      record = CacheMeWithVersion.create
+      record_from_db = CacheMeWithVersion.find(record.id)
+      assert_called(record_from_db, :updated_at) do
+        record_from_db.updated_at = Time.now.to_s
+        record_from_db.cache_version
+      end
+    end
+
+    test "cache_version does call updated_at when it is assigned via a hash" do
+      record = CacheMeWithVersion.create
+      record_from_db = CacheMeWithVersion.find(record.id)
+      assert_called(record_from_db, :updated_at) do
+        record_from_db.updated_at = { 1 => 2016, 2 => 11, 3 => 12, 4 => 1, 5 => 2, 6 => 3, 7 => 22 }
+        record_from_db.cache_version
+      end
+    end
+
+    test "updated_at on class but not on instance raises an error" do
+      record = CacheMeWithVersion.create
+      record_from_db = CacheMeWithVersion.where(id: record.id).select(:id).first
+      assert_raises(ActiveModel::MissingAttributeError) do
+        record_from_db.cache_version
+      end
     end
   end
 end