Wrong time is saved into MySQL DB by Rails' update_all method

Question

I save DateTime.now into datetime column of MySQL DB via Rails', but incorrect value seems saved. The saved value is several tens of seconds past.

My Code:

Rails.logger.info("Start: Calendars.where('user_id = ? and calendar_id = ?', @user.id, calendar_id)")

target = Calendars.where('user_id = ? and calendar_id = ?', @user.id, calendar_id)

Rails.logger.info("End: Calendars.where('user_id = ? and calendar_id = ?', @user.id, calendar_id)")

Rails.logger.info("last_clone_at update start")
now = DateTime.now
target.update_all(last_clone_at: now)

Rails.logger.info(now.strftime("%Y-%m-%dT%H:%M:%S")) # Output by DateTime.now
Rails.logger.info(target.first.last_clone_at) # Saved datetime value

Log output:

2014-06-09 14:39:03 INFO last_clone_at update start
2014-06-09 14:39:03 INFO 2014-06-09T14:39:03 # Output by DateTime.now
2014-06-09 14:39:03 INFO 2014-06-09 14:38:00 +0900 # Saved datetime value

My Calendars model is just as follows:

class Calendars < ActiveRecord::Base

  # Validations
  validates :user_id, presence: true
  validates :calendar_id, presence: true, uniqueness: { scope: :user_id }
end

I use:

• Ruby 2.0
• Rails 4.0.5
• MySQL 5.5.37 (from Ubuntu 14.04 repository)

Update: Other examples of the log output:

2014-06-09 16:28:54 INFO last_clone_at update start
2014-06-09 16:28:54 INFO 2014-06-09T16:28:54
2014-06-09 16:28:54 INFO 2014-06-09 16:28:01 +0900

2014-06-09 16:28:55 INFO last_clone_at update start
2014-06-09 16:28:55 INFO 2014-06-09T16:28:55
2014-06-09 16:28:55 INFO 2014-06-09 16:28:02 +0900

2014-06-09 16:28:57 INFO last_clone_at update start
2014-06-09 16:28:57 INFO 2014-06-09T16:28:57
2014-06-09 16:28:57 INFO 2014-06-09 16:28:04 +0900

Update2: Time to execute Calendars.where(...)

2014-06-09 17:22:06 INFO Start: Calendars.where('user_id = ? and calendar_id = ?', @user.id, calendar_id) 2014-06-09 17:22:06 INFO End: Calendars.where('user_id = ? and calendar_id = ?', @user.id, calendar_id)

Answer 1

I think it is possible. update_all might be "heavy" operation for your DB and it takes some time for updating records (check your logs).

Try to change output:

Rails.logger.info(DateTime.now.strftime("%Y-%m-%dT%H:%M:%S"))
target.update_all(last_clone_at: DateTime.now)
Rails.logger.info(target.first.last_clone_at)`

I think in this way you get much "closer" values.