On Tue, Oct 13, 2009 at 10:14 AM, Kevin Grittner
<Kevin.Grittner@wicourts.gov> wrote:
> Robert Haas <robertmhaas@gmail.com> wrote:
>
>> I sometimes want to know what the planner thinks the cost of some
>> plan other than the one actually selected would be.
>
> Another DBMS I used for years had a way to turn on an *extremely*
> verbose mode for their planner; it showed everything it considered
> with its related cost information. Even a moderately complex query
> generated hundreds or thousands of lines of output, so I rarely used
> it; but for those particularly stubborn queries, where you just can't
> understand why it's picking the plan it is, a little work wading
> through the output would *always* clear up the mystery.
>
> Now that we can generate EXPLAIN output in more structured formats,
> perhaps we could think about adding an "extremely verbose" mode where
> the planner would "think out loud" as a whole separate section from
> where we show the chosen plan?
I wouldn't object to such a thing, but for simple cases I think it
would be more convenient to modify the planner's assumptions and then
try replanning. An exhaustive dump of everything the planner has
considered is going to be a LOT of data, and I don't really want to
have to set up a graphical visualization tool every time I have a
planning question. I am a command-line kind of guy...
...Robert