Hi!
To be fair, I fixed this before [0] by selecting the appropriate group
of "or" expressions to transform them to "ANY" expression and then
checking for compatibility with the index column. maybe we should try
this too? I can think about it.
[0]
https://www.postgresql.org/message-id/531fc0ab-371e-4235-97e3-dd2d077b6995%40postgrespro.ru
On 23.08.2024 15:58, Alexander Korotkov wrote:
Hi!
Thank you for your feedback.
On Fri, Aug 23, 2024 at 1:23 PM Andrei Lepikhov <lepi...@gmail.com> wrote:
On 21/8/2024 16:52, Alexander Korotkov wrote:
/* Only operator clauses scan match */
Should it be:
/* Only operator clauses can match */
?
Corrected, thanks.
I found one more: /* Only operator clauses scan match */ - in the
second patch.
Also I propose:
- “might match to the index as whole” -> “might match the index as a whole“
- Group similar OR-arguments intro dedicated RestrictInfos -> ‘into’
Fixed.
The second one:
When creating IndexClause, we assign the original and derived clauses to
the new, containing transformed array. But logically, we should set the
clause with a list of ORs as the original. Why did you do so?
I actually didn't notice that. Corrected to set the OR clause as the
original. That change turned recheck to use original OR clauses,
probably better this way. Also, that change spotted misuse of
RestrictInfo.clause and RestrictInfo.orclause in the second patch.
Corrected this too.
New findings:
=============
1)
if (list_length(clause->args) != 2)
return NULL;
I guess, above we can 'continue' the process.
2) Calling the match_index_to_operand in three nested cycles you could
break the search on first successful match, couldn't it? At least, the
comment "just stop with first matching index key" say so.
Fixed.
3) I finally found the limit of this feature: the case of two partial
indexes on the same column. Look at the example below:
SET enable_indexscan = 'off';
SET enable_seqscan = 'off';
DROP TABLE IF EXISTS test CASCADE;
CREATE TABLE test (x int);
INSERT INTO test (x) SELECT * FROM generate_series(1,100);
CREATE INDEX ON test (x) WHERE x < 80;
CREATE INDEX ON test (x) WHERE x > 80;
VACUUM ANALYZE test;
EXPLAIN (ANALYZE, COSTS OFF, TIMING OFF)
SELECT * FROM test WHERE x=1 OR x = 79;
EXPLAIN (ANALYZE, COSTS OFF, TIMING OFF)
SELECT * FROM test WHERE x=91 OR x = 81;
EXPLAIN (ANALYZE, COSTS OFF, TIMING OFF)
SELECT * FROM test WHERE x=1 OR x = 81 OR x = 83;
The last query doesn't group clauses into two indexes. The reason is in
match_index_to_operand which classifies all 'x=' to one class. I'm not
sure because of overhead, but it may be resolved by using
predicate_implied_by to partial indexes.
Yes, this is the conscious limitation of my patch: to consider similar
OR arguments altogether and one-by-one, not in arbitrary groups. The
important thing here is that we still generating BitmapOR patch as we
do without the patch. So, there is no regression. I would leave this
as is to not make this feature too complicated. This could be improved
in future though.
------
Regards,
Alexander Korotkov
Supabase
--
Regards,
Alena Rybakina
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
