Re: Problem with default partition pruning - Mailing list pgsql-hackers

Le 19/03/2019 à 08:01, Yuzuko Hosoya a écrit :
> Hi Amit-san,
>
> From: Amit Langote [mailto:Langote_Amit_f8@lab.ntt.co.jp]
> Sent: Monday, March 18, 2019 6:44 PM
>  
>> Hosoya-san,
>>
>> On 2019/03/15 15:05, Yuzuko Hosoya wrote:
>>> Indeed, it's problematic.  I also did test and I found that this
>>> problem was occurred when any partition didn't match WHERE clauses.
>>> So following query didn't work correctly.
>>>
>>> # explain select * from test1_3 where (id > 0 and id < 30);
>>>                            QUERY PLAN
>>> -----------------------------------------------------------------
>>>  Append  (cost=0.00..58.16 rows=12 width=36)
>>>    ->  Seq Scan on test1_3_1  (cost=0.00..29.05 rows=6 width=36)
>>>          Filter: ((id > 0) AND (id < 30))
>>>    ->  Seq Scan on test1_3_2  (cost=0.00..29.05 rows=6 width=36)
>>>          Filter: ((id > 0) AND (id < 30))
>>> (5 rows)
>>>
>>> I created a new patch to handle this problem, and confirmed the query
>>> you mentioned works as expected
>>>
>>> # explain select * from test1 where (id > 0 and id < 30) or (id > 220 and id < 230);
>>>                                 QUERY PLAN
>>> ----------------------------------------------------------------------
>>> -----  Append  (cost=0.00..70.93 rows=26 width=36)
>>>    ->  Seq Scan on test1_1_1  (cost=0.00..35.40 rows=13 width=36)
>>>          Filter: (((id > 0) AND (id < 30)) OR ((id > 220) AND (id < 230)))
>>>    ->  Seq Scan on test1_3_1  (cost=0.00..35.40 rows=13 width=36)
>>>          Filter: (((id > 0) AND (id < 30)) OR ((id > 220) AND (id <
>>> 230)))
>>> (5 rows)
>>>
>>> v2 patch attached.
>>> Could you please check it again?
>> I think the updated patch breaks the promise that get_matching_range_bounds won't set scan_default
>> based on individual pruning value comparisons.  How about the attached delta patch that applies on
>> top of your earlier v1 patch, which fixes the issue reported by Thibaut?
>>
> Indeed.  I agreed with your proposal.
> Also, I confirmed your patch works correctly.
>
> Best regards,
> Yuzuko Hosoya

I kept on testing with sub-partitioning.
I found a case, using 2 default partitions, where a default partition is
not pruned:

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

create table test2(id int, val text) partition by range (id);
create table test2_20_plus_def partition of test2 default;
create table test2_0_20 partition of test2 for values from (0) to (20)
  partition by range (id);
create table test2_0_10 partition of test2_0_20 for values from (0) to (10);
create table test2_10_20_def partition of test2_0_20 default;

# explain (costs off) select * from test2 where id=5 or id=25;
               QUERY PLAN               
-----------------------------------------
 Append
   ->  Seq Scan on test2_0_10
         Filter: ((id = 5) OR (id = 25))
   ->  Seq Scan on test2_10_20_def
         Filter: ((id = 5) OR (id = 25))
   ->  Seq Scan on test2_20_plus_def
         Filter: ((id = 5) OR (id = 25))
(7 rows)

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

I have the same output using Amit's v1-delta.patch or Hosoya's
v2_default_partition_pruning.patch.