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-rw-r--r--activerecord/lib/active_record/integration.rb48
1 files changed, 46 insertions, 2 deletions
diff --git a/activerecord/lib/active_record/integration.rb b/activerecord/lib/active_record/integration.rb
index 456689ec6d..43f6afbb42 100644
--- a/activerecord/lib/active_record/integration.rb
+++ b/activerecord/lib/active_record/integration.rb
@@ -96,8 +96,14 @@ module ActiveRecord
# 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
+ return unless 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
end
@@ -151,5 +157,43 @@ module ActiveRecord
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("- :.")
+ padding = 20 - key.length
+ if padding != 0
+ key << "0" * padding
+ else
+ key
+ end
+ end
end
end