4 files changed, 41 insertions, 8 deletions
diff --git a/activerecord/lib/active_record/integration.rb b/activerecord/lib/active_record/integration.rb
index 19d2589db3..466c8509a4 100644
--- a/activerecord/lib/active_record/integration.rb
+++ b/activerecord/lib/active_record/integration.rb
@@ -10,9 +10,9 @@ module ActiveRecord
       # Indicates the format used to generate the timestamp in the cache key.
       # Accepts any of the symbols in <tt>Time::DATE_FORMATS</tt>.
       #
-      # This is +:nsec+, by default.
+      # This is +:usec+, by default.
       class_attribute :cache_timestamp_format, :instance_writer => false
-      self.cache_timestamp_format = :nsec
+      self.cache_timestamp_format = :usec
     end
 
     # Returns a String, which Action Pack uses for constructing a URL to this
diff --git a/activerecord/test/cases/cache_key_test.rb b/activerecord/test/cases/cache_key_test.rb
new file mode 100644
index 0000000000..bb2829b3c1
--- /dev/null
+++ b/activerecord/test/cases/cache_key_test.rb
@@ -0,0 +1,25 @@
+require "cases/helper"
+
+module ActiveRecord
+  class CacheKeyTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    class CacheMe < ActiveRecord::Base; end
+
+    setup do
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table(:cache_mes) { |t| t.timestamps }
+    end
+
+    teardown do
+      @connection.drop_table :cache_mes, if_exists: true
+    end
+
+    test "test_cache_key_format_is_not_too_precise" do
+      record = CacheMe.create
+      key = record.cache_key
+
+      assert_equal key, record.reload.cache_key
+    end
+  end
+end
diff --git a/activerecord/test/cases/collection_cache_key_test.rb b/activerecord/test/cases/collection_cache_key_test.rb
index 724234d7f4..53058c5a4a 100644
--- a/activerecord/test/cases/collection_cache_key_test.rb
+++ b/activerecord/test/cases/collection_cache_key_test.rb
@@ -53,7 +53,7 @@ module ActiveRecord
 
     test "cache_key with custom timestamp column" do
       topics = Topic.where("title like ?", "%Topic%")
-      last_topic_timestamp = topics(:fifth).written_on.utc.to_s(:nsec)
+      last_topic_timestamp = topics(:fifth).written_on.utc.to_s(:usec)
       assert_match(last_topic_timestamp, topics.cache_key(:written_on))
     end
 
diff --git a/activerecord/test/cases/integration_test.rb b/activerecord/test/cases/integration_test.rb
index 9169207b0a..08a186ae07 100644
--- a/activerecord/test/cases/integration_test.rb
+++ b/activerecord/test/cases/integration_test.rb
@@ -81,7 +81,7 @@ class IntegrationTest < ActiveRecord::TestCase
 
   def test_cache_key_format_for_existing_record_with_updated_at
     dev = Developer.first
-    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_format_for_existing_record_with_updated_at_and_custom_cache_timestamp_format
@@ -111,19 +111,19 @@ class IntegrationTest < ActiveRecord::TestCase
   def test_cache_key_for_updated_on
     dev = Developer.first
     dev.updated_at = nil
-    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_for_newer_updated_at
     dev = Developer.first
     dev.updated_at += 3600
-    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_for_newer_updated_on
     dev = Developer.first
     dev.updated_on += 3600
-    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_format_is_precise_enough
@@ -134,8 +134,16 @@ class IntegrationTest < ActiveRecord::TestCase
     assert_not_equal key, dev.cache_key
   end
 
+  def test_cache_key_format_is_not_too_precise
+    skip("Subsecond precision is not supported") unless subsecond_precision_supported?
+    dev = Developer.first
+    dev.touch
+    key = dev.cache_key
+    assert_equal key, dev.reload.cache_key
+  end
+
   def test_named_timestamps_for_cache_key
     owner = owners(:blackbeard)
-    assert_equal "owners/#{owner.id}-#{owner.happy_at.utc.to_s(:nsec)}", owner.cache_key(:updated_at, :happy_at)
+    assert_equal "owners/#{owner.id}-#{owner.happy_at.utc.to_s(:usec)}", owner.cache_key(:updated_at, :happy_at)
   end
 end