Re: Performance improvement for joins where outer side is unique

David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> On 24 August 2015 at 07:31, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
> wrote:
>> 2) in the explain output, there should probably be a space before the
>> '(inner unique)' text, so
>>
>> Hash Join (inner unique) ...
>>
>> instead of
>>
>> Hash Join(inner unique)
>>
>> but that's just nitpicking at this point. Otherwise the patch seems quite
>> solid to me.

> The attached fixes these two issues.

Please, no. Randomly sticking additional bits of information into Join
Type is a good way to render EXPLAIN output permanently unintelligible,
not only to humans but to whatever programs are still trying to read the
text output format (I think explain.depesz.com still does). It is also
not a great idea to put more semantic distance between the text and
non-text output representations.

I am not exactly convinced that this behavior needs to be visible in
EXPLAIN output at all, but if it does, it should be a separate field.

regards, tom lane