| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Nicolas Barbier <nicolas(dot)barbier(at)gmail(dot)com> |
| Cc: | Antonin Houska <ah(at)cybertec(dot)at>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
| Subject: | Re: Bitmap index scans use of filters on available columns |
| Date: | 2015-11-04 14:54:31 |
| Message-ID: | 1062.1446648871@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Nicolas Barbier <nicolas(dot)barbier(at)gmail(dot)com> writes:
> 2015-11-04 Antonin Houska <ah(at)cybertec(dot)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.
regards, tom lane
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