I think the other situation is that the old cron job is not done yet and the new cron job gets started up. Having a flag in the DB would be able to fix that as well.
On Jul 21, 9:33 pm, Andrew Fong <fongand...@gmail.com> wrote: > >> I was worried by potential caching issues with the database that > >> may prevent my cron script to retrieve the latest boolean value. > > It sounds as if you're worried about a race condition when scale up -- > e.g. let's say you need to run a lot of background processes and > decide to split them up among several machines, each with their own > cron jobs. If Machine A's cron job and Machine B's cron job both check > the database at the same time, they'll both see that the process isn't > running and start it up -- resulting in two copies of the process > instead of just one. > > Am I correct in saying that's what you're concerned about? > > If so, a simple solution would be to just wrap that part of the code > in a transaction. This will ensure Machine B doesn't get a response > back from the database until Machine A finishes updating it. > > Aside from that, this seems fine. > > -- Andrew > > On Jul 21, 9:10 am, Philippe Josse <phildev7...@gmail.com> wrote: > > > Hi there, > > > I would like to have your feedback on the way I am running daemon scripts > > for my Django/ Python app. I know this is definitely not the "one best way", > > but this is a solution I came up with that seemed simple to implement. (I am > > a real newbie!) > > > My constraints: > > - getting a few processs constantly repeating themselves > > - getting an email notification if one of the process crashes > > > I set up a cron job that is launching a "daemon manager" script every > > minute. This script is querying a PostGreSQL database to retrieve boolean > > values associated to the state of my background processes (running / not > > running). If the database indicates the process is not running, then the > > cron script launches it. > > > Boolean values are updated by each process when it starts and finishes. > > Currently, it seems to work fine - but my background processes are very > > quick to execute. When my user base will grow, they may last longer and it > > will be essential that background processes do not run concurrently. > > > Would that solution work? I was worried by potential caching issues with the > > database that may prevent my cron script to retrieve the latest boolean > > value. Is there any real risk? > > > Thanks for your feedback! --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
