Fix serializing of time/date columns using yaml serializer

[fatkodima]

We are currently using paper_trail and have billions of items in the versions table and the table is huge.

I noticed, that for yaml serializer date/time objects are serialized as ruby objects. Something like

--- !ruby/object:ActiveSupport::TimeWithZone
utc: 2024-01-27 18:01:54.627764000 Z
zone: !ruby/object:ActiveSupport::TimeZone
  name: Etc/UTC
time: 2024-01-27 18:01:54.627764000 Z

This generates 179 bytes per field.

But that should be serialized into the string. Something like

--- 2024-01-27 18:03:07 UTC

That is 28 bytes long, so 150 bytes difference.

Considering that most people have at least 2 datetime columns (created_at and updated_at) for each table, that saves 300 bytes per row in the table.
For example, if we have a table with 4 billion rows, that is 4 * 10^9 * 300 / 10^9 = 1200 GB 😱 saved.

• Wrote good commit messages.
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new
  code introduces user-observable changes.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.

[fatkodima]

Ok, this is not working for MySQL (type_cast still returns a Date/Time object instead of String).
But, json serializer in this gem already works as expected and converts it using .as_json. Maybe we should use this too instead of type_cast?

[viral810]

Ok, this is not working for MySQL (type_cast still returns a Date/Time object instead of String). But, json serializer in this gem already works as expected and converts it using .as_json. Maybe we should use this too instead of type_cast?

@fatkodima I think that makes sense to me. I tested out with MySQL and using .as_json returns a string and works as expected.