| From: | Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> |
|---|---|
| To: | David Olbersen <dave(at)slickness(dot)org> |
| Cc: | pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: Optimization via explicit JOINs |
| Date: | 2001-03-09 22:13:35 |
| Message-ID: | Pine.BSF.4.21.0103091409300.82014-100000@megazone23.bigpanda.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-sql |
On Fri, 9 Mar 2001, David Olbersen wrote:
> Greetings,
> I've been toying aroudn with postgres 7.1beta5's ability to control the
> planner via explicitely JOINing tables. I then (just for giggles) compare the
> difference in the EXPLAIN results.
>
> I'm no super-mondo-DBA or anything, but in my two attempts so far, the numbers
> I get out of EXPLAIN have been about 1/2 as small.
>
> Below are two EXPLAIN results, am I correct in reading that one is indeed
> "twice as fast" as the other? I say twice as fast because the top-most cost in
> the first query is 58.62, but in the second one it's only 32.09. Am I reading
> this correctly?
Not entirely. Those are only estimates, so they don't entirely line up
with reality. Also, I notice the first estimates 14 rows and the second
1, which is probably why the estimate is higher. In practice it probably
won't be significantly different.
| From | Date | Subject | |
|---|---|---|---|
| Next Message | David Olbersen | 2001-03-09 22:47:08 | Re: Optimization via explicit JOINs |
| Previous Message | David Olbersen | 2001-03-09 22:00:56 | Optimization via explicit JOINs |