Re: Bitmap index scans use of filters on available columns

Nicolas Barbier <nicolas.barbier@gmail.com> writes:
> 2015-11-04 Antonin Houska <ah@cybertec.at>:
>> (see expand_indexqual_opclause()), I'm not sure any kind of expansion is
>> possible for '%abc%' which would result in a b-tree searchable condition.

> I think the question is not about using the b-tree for checking the
> condition, but about just retrieving the value for y from the index,
> and just using that to check the condition before fetching the
> corresponding tuple from the heap.

Bitmap index scans only return TID bitmaps, not index tuples; indeed
the underlying index may not store anything recognizable as tuples.

postgres=# explain select * from f where x=5 and y like '%abc%';

                                QUERY PLAN                                

--------------------------------------------------------------------------

 Index Scan using f_x_y_idx on f  (cost=0.42..26075.71 rows=209 width=37)
   Index Cond: (x = 5)
   Filter: (y ~~ '%abc%'::text)