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I have a cronjob starting a ruby script (in a rails environment) at the beginning of each hour. The ruby script then makes a series of SQL queries, and looks like this:

def hourly_job
  time = Time.now - 1.hour
  date = time.to_date
  hour = time.hour
  start_time = date.to_time + hour.hours
  end_time = start_time + 1.hour

  Log.where(date: date, hour: hour).delete_all
  count = Event.where('created_at >= ?', start_time).
    where('created_at < ?', end_time).count
  Log.create(date: date, hour: hour, count: count)

The cronjob looks like this (generated by the whenever gem):

0 * * * * /bin/bash -l -c 'cd /path/to/myproj && script/rails runner '\''Log.hourly_job'\'''

This seemed to work fine for a few weeks, but this morning I found that the log table is empty -- something has erased all of my past data, in addition to not logging hourly data until a few hours ago.

An inspection of the MySQL error log revealed no events in the last week, and all of the other table's data seems to be fine, so I don't think it's a DBMS problem.

I'm suspecting some sort of discrepancy between the time that crontab is using and the time given by ruby's Time.now. I'm also exploring the idea that there is something subtly and horribly wrong with my code.

Are there other possible explanations?

Additionally, I am running this project on two separate servers. This data erasing bug has only hit one of them.

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closed as off-topic by Jeff Vanzella, Uri Agassi, Marc-Andre, rolfl, syb0rg Feb 27 '14 at 21:47

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1 Answer 1

Could it be related to timezones? Did daylight savings recently kick in for you locally?

I try to avoid time related accidents by always storing and using UTC, and only converting to local time on display.


To find the root-cause, I'd look at the rails log and find the sql that was used in that delete_all and examine the parameters more closely.

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