What is default ActiveRecord isolation level for transaction

Question

What is default isolation level for transactions in Ruby on Rails for PostgreSQL or MySQL?

active_record/connection_adapters/abstract/database_statements.rb#L173

Answer 1

The documentation states:

  # If your database supports setting the isolation level for a transaction, you can set
  # it like so:
  #
  #   Post.transaction(isolation: :serializable) do
  #     # ...
  #   end

And the code is:

def transaction(requires_new: nil, isolation: nil, joinable: true)

The default value, is nil, which means whatever the default isolation level of the database you are using.

The default value for MySQL is :repeatable_read.

The default value for Postgress is :read_committed.