On Tue, 14 Sep 2010, Merlin Moncure wrote:
np -- this felt particularly satisfying for some reason. btw, I think you have some more low hanging optimization fruit. I think (although it would certainly have to be tested) hiding your attribute description under keyid is buying you nothing but headaches. If you used natural key style, making description primary key of key_description (or unique), and had log_details have a description column that directly referenced that column, your subquery: ( SELECT value FROM log_details d WHERE l.id = d.fk_id AND d.fk_keyid = ( SELECT keyid FROM key_description WHERE description = 'Kesselsolltemperatur' ) ) AS Kesselsolltemperatur, would look like this: ( SELECT value FROM log_details d WHERE l.id = d.fk_id AND d.description = 'Kesselsolltemperatur' ) AS Kesselsolltemperatur, your index on log_details(fk_id, description) is of course fatter, but quite precise...does require rebuilding your entire dataset however. food for thought.
I think your suggestion might be slower because the WHERE clause and possible JOINS with BIGINT is much faster (especially when a lot of data is queried) than with a VARCHAR. With the latest query plan key_description is only queried once per subselect which is perfect. I've also chosen that indirection that I can change description without changing too much in data model and all data rows on refactoring.
@Tom: Do you think of planner enhancements regarding such situations where JOINS are "converted" to subselects?
BTW: I had a small bug in the queries and in the code that one description was wrong (one space too much: 'Meldung F4 2. Zeile' => 'Meldung F4 2. Zeile'). With this indirect data model this is very easy to change: Change the view and change one code line. With your suggested data model I would have to update millions of rows ...
Ciao, Gerhard -- http://www.wiesinger.com/ -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
