On Thu, Dec 15, 2011 at 5:56 AM, Sells, Fred <fred.se...@adventistcare.org>wrote:
> I’ve got an older app that’s been running in production for about 2 years > on RedHat 4, MySQL 5.0.77 with MyISAM tables, Django 1.2.1 and Python 2.4. > **** > > ** ** > > This app is used heavily by internal users, which is a relatively light > load compared to public sites. I actually use Flex for the client side and > save each field when the user changes it.**** > > ** ** > > About once a month one field in particular will have its value cleared, or > perhaps the save operation did not complete before the next user input hits > the server. I’ve searched my code for an unexpected reference to this > field name with no results. As I understand it, Django is single threaded > so I don’t know how this can happen. > The Django code itself is not multithreaded -- it spawns no threads of its own -- but that doesn't mean that your setup is single-threaded. That depends entirely on how your web server is configured. Every production environment I have seen uses processes or threads to serve multiple requests simultaneously, which means that multiple instances of the Django code are running at any given time. Django tries to be thread-safe, which is slightly different -- the code is written such that multiple threads can co-exist without stomping all over each other's data, at least at the Python level. At the database level, things are different again. This is probably where your problems are coming from. If your database doesn't support isolation through transactions (if you're using MyISAM tables on MySQL, basically), then you are susceptible to problems like this. Database operations can and will be interleaved, depending on when and how your web server decides to schedule its threads. > **** > > ** ** > > Has anyone seen similar behavior? I plan to upgrade next month anyway, > but could this be an artifact of the older Django or of MyISAM tables? > I doubt that upgrading Django will solve anything, but I would recommend upgrading your tables to InnoDB. The only reasons I know for sticking with MyISAM are a requirement for speed over all else (including data integrity), and to use the MySQL "full-text-search" feature. I’m not using transactions since I’m not an experienced DBA, but should I? > Happily, Django will take care of all of this for you; you don't have to be a DBA, or even think about transactions most of the time. As long as your database supports it, Django will automatically isolate each request in its own transaction. If the view returns a response, the transaction will be committed to the database, and if the view raises error, the transaction will be rolled back automatically. In almost every case, this behaviour will be exactly what you want. -- Regards, Ian Clelland <clell...@gmail.com> -- 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.
