Re: PATCH: index-only scans with partial indexes - Mailing list pgsql-hackers

On 09/29/2015 04:57 PM, Tomas Vondra wrote:
> Hello,
>
> On 09/29/2015 12:27 PM, Kyotaro HORIGUCHI wrote:

...

>>
>> cost_index() seems to need to be fixed. It would count excluded
>> clauses in estimate.
>
> Hmm, good point. The problem is that extract_nonindex_conditions uses
> baserel->baserestrictinfo again, i.e. it does not skip the implied
> clauses. So we may either stick the filtered clauses somewhere (for
> example in the IndexPath), teach extract_nonindex_conditions to use
> predicate_implied_by. I'd say the first option is better. Agreed?

And the attached patch v4 should do the trick - it adds 'indexrinfos' to
IndexPath and uses it in cost_index().

CREATE TABLE t AS SELECT i AS a, i AS b, i AS c
                     FROM generate_series(1,1000) s(i);

CREATE INDEX idx ON t(a) WHERE b > 1000;

Then

SELECT a FROM t WHERE b > 1000 AND a < 1000; /* size(qpquals) = 0 */
SELECT a FROM t WHERE b > 1000 AND c < 1000; /* size(qpquals) = 1 */
SELECT a FROM t WHERE c > 1000 AND c < 1000; /* size(qpquals) = 2 */

and so on. Which seems correct I believe.

regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
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