django multiprocess problem

Question

I have django application, running under lighttpd via fastcgi. FCGI running script looks like:

python manage.py runfcgi socket=<path>/main.socket
    method=prefork \                                                                                                    
    pidfile=<path>/server.pid \                                                                                                                                        
    minspare=5 maxspare=10 maxchildren=10 maxrequests=500 \

I use SQLite. So I have 10 proccess, which all work with the same DB. Next I have 2 views:

def view1(request)
    ...
    obj = MyModel.objects.get_or_create(id=1)
    obj.param1 = <some value>
    obj.save ()

def view2(request)
    ...
    obj = MyModel.objects.get_or_create(id=1)
    obj.param2 = <some value>
    obj.save ()

And If this views are executed in two different threads sometimes I get MyModel instance in DB with id=1 and updated either param1 or param2 (BUT not both) - it depends on which process was the first. (of course in real life id changes, but sometimes 2 processes execute these two views with same id)

The question is: What should I do to get instance with updated param1 and param2? I need something for merging changes in different processes.

One decision is create interprocess lock object but in this case I will get sequence executing views and they will not be able to be executed simultaneously, so I ask help

DUPE OF Django: How can I protect against concurrent modification of data base entries

Answer 1

SQLite is not good choice if you need such concurrent access to database. I suggest switching to some other rdbms, like MySQL or PostgreSQL, and also take into account get_or_create fragility:

http://stackoverflow.com/questions/2235318/how-do-i-deal-with-this-race-condition-in-django/2235624#2235624

Regarding the above link, there is also second solution to that problem - using READ COMMITED isolation level, instead of REPEATABLE READ. But it's less tested (At least in MySQL), so there might be more bugs/problems with it.