Hi!
Here's an odd thing. I use a partial index on a table:
group_data
CREATE TABLE group_data ( this_group_id integer NOT NULL, group_id integer
-- ...
);
create index foo on group_data(this_group_id) where group_id is null;
there are approx 1 million tuples where this_group_id=46, but only 4 (four)
where group_id is null. So I would expect this query to use the index:
select * from group_data where this_group_id=46 and group_id is null.
On 7.4.5, it uses the index, but on 8.0rc5, it does not:
7.4.5=# explain analyze select * from group_data where group_id is null and
this_group_id = 46; QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------Index
Scanusing foo on group_data (cost=0.00..40383.21 rows=108786
width=43) (actual time=0.154..0.176 rows=4 loops=1) Index Cond: (this_group_id = 46) Filter: (group_id IS NULL)Total
runtime:0.241 ms
(4 rows)
8.0.0rc5=# explain analyze select * from group_data where group_id is null
and this_group_id = 46; QUERY PLAN
---------------------------------------------------------------------------------------------------------------------Seq
Scanon group_data (cost=0.00..140180.91 rows=211378 width=45)
(actual time=383.689..32991.424 rows=4 loops=1) Filter: ((group_id IS NULL) AND (this_group_id = 46))Total runtime:
32991.469ms
(3 rows)
Time: 32992.812 ms
This is bad. But it gets worse:
8.0.0rc5=# explain analyze select * from group_data where group_id is null
and this_group_id = 46 and this_group_id = 46; QUERY
PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------Index
Scanusing group_data_tgid_gidnull_idx on group_data
(cost=0.00..145622.85 rows=78985 width=45) (actual time=0.033..0.039 rows=4
loops=1) Index Cond: ((this_group_id = 46) AND (this_group_id = 46)) Filter: (group_id IS NULL)Total runtime: 0.086
ms
(4 rows)
Time: 1.912 ms
Don't tell me this is not a bug?
this_group_id = 46 and
this_group_id = 46
seems like a pretty odd way to get a query to use an index?
Need more specific info, please mail me!
Regards,
Palle
