On Tue, Apr 3, 2012 at 12:30 PM, Jon Nelson <jnelson+pgsql@xxxxxxxxxxx> wrote: > On Tue, Apr 3, 2012 at 12:16 PM, Merlin Moncure <mmoncure@xxxxxxxxx> wrote: >> On Tue, Apr 3, 2012 at 12:01 PM, Jon Nelson <jnelson+pgsql@xxxxxxxxxxx> wrote: >>> I have a situation that I'd like some help resolving. >>> Using PostgreSQL 8.4.<reasonably recent> on Linux, I have three things >>> coming together that cause me pain. I have a VIEW used by a bunch of >>> queries. Usually, these queries are fairly short (subsecond) but >>> sometimes they can be very long (days). I also update this view with >>> CREATE OR REPLACE VIEW every 15-30 minutes. What I observe, sometimes, >>> is this: >>> >>> 1. query A comes in. It's a big one. >>> 2. another process comes along, needs to update the view definition. >>> It issues create or replace view. It blocks on [1]. >>> 3. queries B through N come in, are blocked by [2], which is blocked by [1]. >>> 4. pandemonium! >>> >>> I can reduce (some) but not eliminate the need to update the view >>> multiple times a day. What might be some good ways to prevent queries >>> B through N blocking? >>> >>> Addendum: I can work around the issue by timing out and failing the >>> CREATE OR REPLACE VIEW (by canceling the query) after a short >>> duration, but is there a better way? >> >> Yeah -- this is just asking for trouble. Why do you have to replace >> the view every 30 minutes? Your solution is probably going to involve >> not doing that. > > As I said, I can reduce the frequency, but not eliminate it. I'm > curious - if views are little more than sql macros, by the time the > query has begun to execute why is a lock still needed on the view > definition? Generally speaking, in SQL, locks are held until the transaction commits; there are tons of reasons why things have to work that way. Anyways, I'm betting your requirement to have to re-CREATE the view can be abstracted out somehow. I'm guessing you have some type of table rotation going on? merlin -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
