The connection is not properly checked-out of the connection pool. AR may give it to other threads to use

data_load.rb

module DataLoad
  class Thing1

    def reload_all
      connection = ActiveRecord::Base.connection
    
      sql = <<-SQL
      create temporary table tmp_thing1 (
        -- ...
      )
      SQL
      connection.execute(sql)
  
      sql = <<-SQL
      --  Load data
      SQL
      connection.execute(sql)

      sql = <<-SQL
      --  Do things with the data
      SQL
      connection.execute(sql)
    end
  end
end