Re: POC, WIP: OR-clause support for indexes

On 29.11.2024 03:04, Alexander Korotkov wrote:
> On Thu, Nov 28, 2024 at 9:33 PM Alena Rybakina
> <a(dot)rybakina(at)postgrespro(dot)ru> wrote:
>> On 28.11.2024 22:28, Ranier Vilela wrote:
>>
>> Em qui., 28 de nov. de 2024 às 16:03, Alena Rybakina <a(dot)rybakina(at)postgrespro(dot)ru> escreveu:
>>> Hi! Thank you for the case.
>>>
>>> On 28.11.2024 21:00, Alexander Lakhin wrote:
>>>> Hello Alexander,
>>>>
>>>> 21.11.2024 09:34, Alexander Korotkov wrote:
>>>>> I'm going to push this if no objections.
>>>> Please look at the following query, which triggers an error after
>>>> ae4569161:
>>>> SET random_page_cost = 1;
>>>> CREATE TABLE tbl(u UUID);
>>>> CREATE INDEX idx ON tbl USING HASH (u);
>>>> SELECT COUNT(*) FROM tbl WHERE u = '00000000000000000000000000000000' OR
>>>> u = '11111111111111111111111111111111';
>>>>
>>>> ERROR: XX000: ScalarArrayOpExpr index qual found where not allowed
>>>> LOCATION: ExecIndexBuildScanKeys, nodeIndexscan.c:1625
>>>>
>>>>
>>> I found out what the problem is index scan method was not generated. We
>>> need to check this during OR clauses for SAOP transformation.
>>>
>>> There is a patch to fix this problem.
>> Hi.
>> Thanks for the quick fix.
>>
>> But I wonder if it is not possible to avoid all if the index is useless?
>> Maybe moving your fix to the beginning of the function?
>>
>> diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
>> index d827fc9f4d..5ea0b27d01 100644
>> --- a/src/backend/optimizer/path/indxpath.c
>> +++ b/src/backend/optimizer/path/indxpath.c
>> @@ -3248,6 +3248,10 @@ match_orclause_to_indexcol(PlannerInfo *root,
>> Assert(IsA(orclause, BoolExpr));
>> Assert(orclause->boolop == OR_EXPR);
>>
>> + /* Ignore index if it doesn't support index scans */
>> + if(!index->amsearcharray)
>> + return NULL;
>> +
>>
>> Agree. I have updated the patch
>>
>> /*
>> * Try to convert a list of OR-clauses to a single SAOP expression. Each
>> * OR entry must be in the form: (indexkey operator constant) or (constant
>>
>> The test bug:
>> EXPLAIN SELECT COUNT(*) FROM tbl WHERE u = '00000000000000000000000000000000' OR u = '11111111111111111111111111111111';
>> QUERY PLAN
>> ----------------------------------------------------------------------------------------------------------------------------------
>> Aggregate (cost=12.46..12.47 rows=1 width=8)
>> -> Bitmap Heap Scan on tbl (cost=2.14..12.41 rows=18 width=0)
>> Recheck Cond: ((u = '00000000-0000-0000-0000-000000000000'::uuid) OR (u = '11111111-1111-1111-1111-111111111111'::uuid))
>> -> BitmapOr (cost=2.14..2.14 rows=18 width=0)
>> -> Bitmap Index Scan on idx (cost=0.00..1.07 rows=9 width=0)
>> Index Cond: (u = '00000000-0000-0000-0000-000000000000'::uuid)
>> -> Bitmap Index Scan on idx (cost=0.00..1.07 rows=9 width=0)
>> Index Cond: (u = '11111111-1111-1111-1111-111111111111'::uuid)
>> (8 rows)
> I slightly revised the fix and added similar check to
> group_similar_or_args(). Could you, please, review that before
> commit?
>
I agree with changes. Thank you!

--
Regards,
Alena Rybakina
Postgres Professional