On 2 June 2017 at 03:46, Teodor Sigaev <teo...@sigaev.ru> wrote: > I miss here why could the presence of index influence on that? removing > index causes a good plan although it isn't used in both plans .
Unique indexes are used as proofs when deciding if a join to the relation is "inner_unique". A nested loop unique join is costed more cheaply than a non-unique one since we can skip to the next outer tuple once we've matched the current outer tuple to an inner tuple. In theory that's half as many comparisons for a non-parameterised nested loop. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
