tmp <[EMAIL PROTECTED]> writes: > Regarding whether it's worth the effort: In each of my three past jobs (all > using postgresql) I have met several queries that would fetch a small subset > of > a large - even huge - input. I think that types of queries are relatively > common out there, but if they are executed for e.g. a web-client it is simply > a > no-go with the current late LIMIT evaluation. > > Also, it is my impression that many people use LIMIT to minimize the > evaluation > time of sub queries from which the outer query only needs a small subset of > the > sub query output.
I've seen lots of queries which only pull a subset of the results too -- but it's always a specific subset. So that means using ORDER BY or a WHERE clause to control it. In this example the subset returned is completely arbitrary. That's a much finer slice of queries. I would tend to think it's worth it myself. I can see cases where the subset selected doesn't really matter -- for instance if you're only testing whether there are at least a certain number of distinct values. Or if you're using up some inventory and it's not important what order you use them up only that you fetch some candidate inventory and process them. But I can also see Tom's reluctance. It's a fair increase in the amount of code to maintain in that file for a pretty narrow use case. On the other hand it looks like it would be all in that file. The planner wouldn't have to do anything special to set it up which is nice. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's 24x7 Postgres support! -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
