Re: Performance improvement for joins where outer side is unique - Mailing list pgsql-hackers

On 13 March 2015 at 20:34, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote:

 

For all that, I agree that the opition that this kind of separate
multiple-nested loops on relations, joins or ECs and so on for
searching something should be avoided. I personally feel that
additional time to such an extent (around 1%) would be tolerable
if it affected a wide range of queries or it brought more obvious
gain.

For testing, I added some code to mark_unique_joins() to spit out a NOTICE:

if (eclassjoin_is_unique_join(root, joinlist, rtr))

{

root->simple_rel_array[rtr->rtindex]->is_unique_join = true;

elog(NOTICE, "Unique Join: Yes");

}

else

elog(NOTICE, "Unique Join: No");

and the same below for special joins too.

On running the regression tests I see:

"Unique Join: Yes"  1557 times

"Unique Join: No" 11563 times