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.