Re: Querying in a loop - cached results?

On Sun, Aug 8, 2010 at 1:03 PM, Nick Arnett <nick.arnett@gmail.com> wrote:

I'm having a problem that I can't figure out from reading the docs.  I have a loop that runs the same query every five minutes, to see if there is new data to process.  However, it doesn't return the new data the second and subsequent times it loops.  It's something like this:

while 1:
     data = Foo.objects.filter(not_analyzed=True)
     if len(data):
          for item in data:
               do_analysis(item)
     sleep(300)

Even though I know there is new data added while it is sleeping, the query doesn't return it.  If I kill the process and re-start, it finds the new data, so it smells like a caching problem... but I don't see anything in the documentation that would suggest this.  It shouldn't be the database query cache (MySQL) because it should know the data has changed.

I've tried adding "del data" at the bottom of the loop, but that didn't help - thought maybe if I explicitly deleted the data, that would work.

Any ideas what's going on or how to solve this?

Probably you are seeing the effects of the default transaction isolation level on MySQL/InnoDB, which is "repeatable read". See http://groups.google.com/group/django-users/browse_thread/thread/e25cec400598c06d for more explanation.

Karen

--
http://tracey.org/kmt/

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