Re: generic options for explain

Greg Smith <gsmith@gregsmith.com> writes:
> On Sun, 24 May 2009, Pavel Stehule wrote:
>> we should have a secondary function explain_query(query_string,
>> option) that returns setof some.

> +1.  The incremental approach here should first be adding functions that 
> actually do the work required.  Then, if there's a set of those that look 
> to be extremely useful, maybe at that point it's worth talking about how 
> to integrate them into the parser.  Starting with the parser changes 
> rather than the parts that actually do the work is backwards.  If you do 
> it the other way around, at all times you have a patch that actually 
> provides immediate useful value were it to be committed.

> Something that returns a setof can also be easily used to implement the 
> "dump EXPLAIN to a table" feature Josh Tolley brought up (which is another 
> common request in this area).

A serious problem with EXPLAIN via a function returning set, or with
putting the result into a table, is that set results are logically
unordered, just as table contents are.  So from a strict point of view
this only makes sense when the output format is designed to not depend
on row ordering to convey information.  We could certainly invent such
a format, but I think it's a mistake to go in this direction for
EXPLAIN output that is similar to the current output.
        regards, tom lane