Hi Robert,
On 05/24/2009 02:47 AM, Robert Haas wrote:
Well, here we are! Yet another thread about some piece of information
that's omitted from EXPLAIN and can't easily be added because there
are a zillion things we want to add to EXPLAIN and it's not OK to bury
the user[1]! I've long been of the opinion that the right way to fix
this problem is to extend the syntax with some sort of extensible
options syntax[2]. The current "EXPLAIN [ANALYZE] [VERBOSE]<query>"
syntax does not scale to large numbers of options - it requires that
the options occur in a fixed order, and that the option names all be
keywords. Having gotten throughly fed up with having this
conversation for the ump-teenth time, I wrote a patch to introduce
just such a syntax. See attached.
What I did is borrowed the generic options stuff that Peter Eisentraut
introduced for FOREIGN DATA WRAPPER et. al, so you can write:
EXPLAIN (option_name1 "option_value1", option_name2 "option_value2") query
e.g. EXPLAIN (ANALYZE "on") query
Beeing the latest cause for the frustration leading to this patch I
obviously would like something like that - and I would gladly implement
some additional stats suggested by others(if implementable in a
reasonable timeframe) if this approach is agreed uppon.
- I noticed that we currently acce pt as a top-level SQL command an
arbitrarily parenthesized SELECT statement, like ((SELECT 3)). But
you can't put parentheses around any other type of statement. Even
more oddly, we also accept things like (SELECT 3) ORDER BY 1, which to
me makes no sense at all.
I would guess that stems from supporting syntax like:
(SELECT 1)
UNION
(SELECT 2)
ORDER BY
and not wanting to introduce a special path for
(SELECT 1)
ORDER BY
For additional stats to be kept another discussion about appropriate,
extensible representation suitable for different output formats probably
would be needed - but thats a discussion for another day.
Andres
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