WireSpot wrote: > On Thu, Nov 20, 2008 at 15:05, Craig Ringer <craig@xxxxxxxxxxxxxxxxxxxxx> wrote: >> That's probably going to be the case. PostgreSQL won't need to read the >> redundant info in from disk each time, and relative to the image data it's >> going to be pretty small. By doing it all in one join you're avoiding the >> overhead of all those network round trips (if on a network), statement >> preparation and planning, etc etc etc. Additionally, PostgreSQL is probably >> going to be using a join plan that's much more efficient than anything >> you'll get by looping over each user and asking for images. > > How about if the subset of images for each user is randomized? As in > ORDER BY RANDOM() LIMIT 3. I'm guessing that will put somewhat of a > cramp on the big join scenario and perhaps it becomes better to have > the RANDOM() in the small individual selects? I'm not even sure how you'd achieve that (exactly 3 randomly selected images per user) in with a single query. Then again, it's stupidly late here, so my brain may not be working. Any chance you can post a query that shows what you're doing? -- Craig Ringer -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
