That looks really useful - for future reference, great! Sadly my webhost is still bundling Django 1.2.3 :(
In general, though, these issues still come down to the fact that a SQL query as executed by Django takes several times longer than going directly to the DB. Is this down to my use of dictfetchall() or something more low level? On Tuesday, January 22, 2013 12:09:50 PM UTC, Jani Tiainen wrote: > > Hi, > > I see that you had quite a bunch of m2m keys. > > Have you tried recent version of Django (1.4+) with prefetch_related() [1] > ? > > > [1] > < > https://docs.djangoproject.com/en/1.4/ref/models/querysets/#prefetch-related> > > > > 22.1.2013 13:57, Matt Andrews kirjoitti: > > Hi Jani, > > > > I made a StackOverflow post last year with an example of the ORM stuff I > > tried and the poor queries it produced: > > > http://stackoverflow.com/questions/5843457/django-objects-all-making-360-queries-how-can-i-optimise-this-manytomany > > > > > There's also this discussion about how using the same queryset in two > > places in the template caused Django to request its data twice: > > > http://stackoverflow.com/questions/9447053/best-way-to-slice-a-django-queryset-without-hitting-the-database-more-than-once(this > > > was easily fixed, but again, not very intuitive and frustrated me) > > > > I don't have the data to hand currently but I also remember seeing weird > > things happen where queries would end with stuff like "... LIMIT > > 234423445" (or some crazy number which I'd never entered and was orders > > of magnitude bigger than the number of rows in the table). > > > > I'm aware these are probably edge cases that are down to my own novice > > status, but even using things like select_related(), it wasn't doing > > what I wanted. I just felt it easier to use my existing SQL (I'm > > converting a PHP app over to Django) and I'm not concerned about > > database portability (switching to postgres or whatever). > > > > Nik: just realised I missed your final question. For the SQL posted > > above, the numbers are approximately: 12,000 rows in the `news` table, > > maybe 10 `news_category` rows, about 100 `writers` and around 3000 > > `images`. All properly indexed and with sensible column types. > > > > On Tuesday, January 22, 2013 10:53:40 AM UTC, Jani Tiainen wrote: > > > > Hi, > > > > From your raw SQL I saw you're doing few joins. So I suppose you > do > > quite a few foreign key fetches. > > > > You didn't mention anything how you originally tried to solve case > with > > ORM. Could you please publish what you had when things were slow? > > > > 22.1.2013 12:26, Matt Andrews kirjoitti: > > > Hi Nik, > > > > > > Thanks - I do feel like by circumventing the ORM I've just "given > > up" > > > and perhaps I'll reconsider -- none of my queries are > particularly > > > "specialist" (as the sample above indicates) - I just found > Django > > > generating odd things. > > > > > > To answer your questions: > > > > > > 1. Yes, reloading the page sees the same time for the queries (it > > just > > > feels as though the entire process takes a second or two to > > start, which > > > is perhaps not related to SQL itself). > > > > > > 2. I believe so, yes (it's shared hosting...). > > > > > > If you're curious, you can see a sample of the app at > > > http://beta.scenepointblank.com <http://beta.scenepointblank.com> > > > (obviously you won't see the SQL, but > > > the "delay" between pages, even though these pages are all cached > > for > > > 2hrs+, is partly my concern here). > > > > > > On Tuesday, January 22, 2013 4:24:09 AM UTC, Nikolas > > Stevenson-Molnar wrote: > > > > > > Hi Matt, > > > > > > Firstly, I encourage you to have another crack a the ORM. It > can > > > certainly seem a bit aggravating at times if you're coming > > from a > > > SQL mindset, but really pays off down the road in terms of > > > maintainability and readability. Typically you should only > > need raw > > > queries in Django in cases where you have super-specialized > > (that > > > uses views or non-standard functions) queries or need some > > specific > > > optimization. If there's really no way to perform many of > your > > > "day-to-day" queries with the ORM then that's an indication > > that a > > > different database design may fit your data model better. I > > > understand that you may have a unique situation, but I just > > wanted > > > to throw that out there as I personally find the ORM to be a > > huge > > > time saver. > > > > > > Now, with that out of the way... a couple of considerations: > > 1) you > > > say it's a slow "startup"; if you refresh the page do the > > queries > > > run just as slow the second time around? and 2) are your > > Django app > > > and phpMyAdmin running on the same machine? If not, could > > transit > > > time be an issue? > > > > > > Finally, can you give an idea about the size of the tables in > > > question? How many rows in each? > > > > > > _Nik > > > > > > On 1/21/2013 3:25 PM, Matt Andrews wrote: > > >> Hi all, > > >> > > >> Fairly new to Django. I ended up pulling out all of the > > >> ORM-generated queries and writing my own SQL directly (I got > > fed > > >> up trying to work out how to achieve the kind of things I > > needed > > >> without Django adding in extra joins or unintended WHERE > > clauses > > >> etc). All my app's SQL uses cursor.execute() and the > > >> dictfetchall() method as referenced here > > >> > > < > https://docs.djangoproject.com/en/dev/topics/db/sql/#django.db.models.Manager.raw > > > < > https://docs.djangoproject.com/en/dev/topics/db/sql/#django.db.models.Manager.raw>>. > > > > > > >> > > >> > > >> I've found that my app incurs a couple of seconds load time > in > > >> production, with CPU time at 2532ms and overall time 4684ms > > >> (according to the debug toolbar). I'm seeing 8 SQL queries > take > > >> 380ms, and each one seems to be several times slower when > > made by > > >> Django versus hitting the database through phpMyAdmin or > > >> something: eg, this query: > > >> > > >> SELECT * FROM news > > >> JOIN news_categories ON news.news_category_id = > > >> news_categories.id <http://news_categories.id> > > <http://news_categories.id> > > >> LEFT JOIN writers ON news.writer_id = writers.id > > <http://writers.id> > > >> <http://writers.id> > > >> LEFT JOIN images ON news.image_id = images.id > > <http://images.id> <http://images.id> > > >> ORDER BY news.is_sticky DESC, news.date_posted DESC > > >> LIMIT 10 > > >> > > >> > > >> This takes 14.8ms when run in phpMyAdmin (against the > > production > > >> database) but Django reports it as 85.2ms. The same ratios > are > > >> true for all my other queries. > > >> > > >> All I can think of is the note on the dictfetchall() method > > in the > > >> Django docs which describes a "small performance hit". Is > > this it?! > > >> > > >> I've profiled the app too, although I'm a bit hazy about > > what it > > >> all means. Here's a dump of the result: > > >> http://pastebin.com/raw.php?i=UHE9edVC > > <http://pastebin.com/raw.php?i=UHE9edVC> > > >> <http://pastebin.com/raw.php?i=UHE9edVC > > <http://pastebin.com/raw.php?i=UHE9edVC>> (this is from running on > > >> my local server rather than production but performance is > > broadly > > >> similar). > > >> > > >> Can anyone help me? I realise I've perhaps gone off-piste by > > >> writing raw SQL but I feel it was justified. > > >> > > >> thanks, > > >> Matt > > >> > > > > -- > > Jani Tiainen > > > > - Well planned is half done and a half done has been sufficient > > before... > > > > -- > > You received this message because you are subscribed to the Google > > Groups "Django users" group. > > To view this discussion on the web visit > > https://groups.google.com/d/msg/django-users/-/H1vytr_AuFIJ. > > To post to this group, send email to > > django...@googlegroups.com<javascript:>. > > > To unsubscribe from this group, send email to > > django-users...@googlegroups.com <javascript:>. > > For more options, visit this group at > > http://groups.google.com/group/django-users?hl=en. > > > -- > Jani Tiainen > > - Well planned is half done and a half done has been sufficient before... > -- You received this message because you are subscribed to the Google Groups "Django users" group. 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