Hi Russ, Makes sense. Thanks.
Collin On Sunday, December 21, 2014 5:41:34 PM UTC-6, Russell Keith-Magee wrote: > > > On Sun, Dec 21, 2014 at 12:55 PM, Collin Anderson <[email protected] > <javascript:>> wrote: >> >> Hi Erik, >> >> If you want a nicer interface, I just ran manage.py inspecdb on one of my >> databases and got this for the cache table. Not sure why django still does >> it by hand. >> > > Gather `round, children, and let Grandpa fill you in on the details... :-) > > Although it isn't huge, Django's ORM does have an overhead. If you're > looking for the general capability to query rows on a database, this > overhead is a reasonable price to pay - you have a little overhead, but > it's a lot easier to express complex queries. However, in the case of a > cache table, you need to issue exactly 2 queries: > > 1) Get me the object with key X. > > 2) Set the value of key X. > > These two queries are trivial to write -- so trivial in fact, that they > don't even need to rewritten as they move across database backends. They're > as "vanilla" as a query can get in SQL. > > So - this becomes a case study in when *not* to use the ORM. We know the 2 > queries that need to be issued. That SQL isn't hard to write or maintain. > And using the ORM would impose a non-trivial runtime overhead - and by > definition, a cache backend is supposed to be as efficient as possible. Raw > SQL is the "right" answer here. > > (well.... not using a database backed cache backend is the *really* right > answer, but I'll let that slide for the moment...) > > If you *do* want to do complex queries on the database cache table, the > approach suggested by Collin is as good an approach as any. A managed table > will give you ORM operations over an arbitrary table - include Django's own > internal tables. > > That said, I'll also concur that the database cache backend is the wrong > answer here. If you're writing a cron script, the approach I've always used > is PIDfile based lock: > > > http://unix.stackexchange.com/questions/12815/what-are-pid-and-lock-files-for > > Yours, > Russ Magee %-) > -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/d3674731-8421-4ec8-a208-8290e7486330%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
