Elver Loho wrote: > Hiya! > > Someone raised this question in the comments of the 4th tutorial and > it's been bugging me to no end. > > Let's take the poll sample. We've got the vote() view going on. > > choice.votes += 1 > choice.save() > > Suppose we've got thread1 and thread2 going on (high-load website): > > choice.votes is originally 16 > > thread1.choice.votes += 1 > thread2.choice.votes += 1 > thread1.choice.save() > thread2.choice.save() > > choice.votes _should_ be 18 now, but is it 18 or 17?
To avoid more or less undefined behaviour, usually in SQL you'd do something like SELECT votes FROM choice FOR UPDATE WHERE ... This blocks one of the threads until the other's transaction ends. But I wonder: Is there a way in Django to do this? I haven't found a way in the DB API to enable "FOR UPDATE". Another way to do this: You could use the transaction middleware to create separate transactions for each of the threads, and put your database in serial transaction isolation mode (no idea if mysql or postgresql support this it all), then one of the transactions would get an error from the database, which could be handled by doing the transaction again. Michael --~--~---------~--~----~------------~-------~--~----~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users -~----------~----~----~----~------~----~------~--~---
