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

On Wed, Jan 31, 2024 at 7:10 PM Alena Rybakina
<a.rybakina@postgrespro.ru> wrote:
>
> Hi, thank you for your review and interest in this subject.
>
> On 31.01.2024 13:15, jian he wrote:
>
> On Wed, Jan 31, 2024 at 10:55 AM jian he <jian.universality@gmail.com> wrote:
>
> based on my understanding of
> https://www.postgresql.org/docs/current/xoper-optimization.html#XOPER-COMMUTATOR
> I think you need move commutator check right after the `if
> (get_op_rettype(opno) != BOOLOID)` branch
>
> I was wrong about this part. sorry for the noise.
>
>
> I have made some changes (attachment).
> * if the operator expression left or right side type category is
> {array | domain | composite}, then don't do the transformation.
> (i am not 10% sure with composite)
>
> To be honest, I'm not sure about this check, because we check the type of variable there:
>
> if (!IsA(orqual, OpExpr))
>         {
>             or_list = lappend(or_list, orqual);
>             continue;
>         }
> And below:
> if (IsA(leftop, Const))
>         {
>             opno = get_commutator(opno);
>
>             if (!OidIsValid(opno))
>             {
>                 /* Commuter doesn't exist, we can't reverse the order */
>                 or_list = lappend(or_list, orqual);
>                 continue;
>             }
>
>             nconst_expr = get_rightop(orqual);
>             const_expr = get_leftop(orqual);
>         }
>         else if (IsA(rightop, Const))
>         {
>             const_expr = get_rightop(orqual);
>             nconst_expr = get_leftop(orqual);
>         }
>         else
>         {
>             or_list = lappend(or_list, orqual);
>             continue;
>         }
>
> Isn't that enough?

alter table tenk1 add column arr int[];
set enable_or_transformation to on;
EXPLAIN (COSTS OFF)
SELECT count(*) FROM tenk1
WHERE arr = '{1,2,3}' or arr = '{1,2}';

the above query will not do the OR transformation. because array type
doesn't have array type.
`
scalar_type = entry->key.exprtype;
if (scalar_type != RECORDOID && OidIsValid(scalar_type))
array_type = get_array_type(scalar_type);
else
array_type = InvalidOid;
`

If either side of the operator expression is array or array related type,
we can be sure it cannot do the transformation
(get_array_type will return InvalidOid for anyarray type).
we can check it earlier, so hash related code will not be invoked for
array related types.


> Besides, some of examples (with ARRAY) works fine:
>
> postgres=# CREATE TABLE sal_emp (
>     pay_by_quarter  integer[],
>     pay_by_quater1 integer[]
> );
> CREATE TABLE
> postgres=# INSERT INTO sal_emp
>     VALUES (
>     '{10000, 10000, 10000, 10000}',
>     '{1,2,3,4}');
> INSERT 0 1
> postgres=# select * from sal_emp where pay_by_quarter[1] = 10000 or pay_by_quarter[1]=2;
>       pay_by_quarter       | pay_by_quater1
> ---------------------------+----------------
>  {10000,10000,10000,10000} | {1,2,3,4}
> (1 row)
>
> postgres=# explain select * from sal_emp where pay_by_quarter[1] = 10000 or pay_by_quarter[1]=2;
>                           QUERY PLAN
> --------------------------------------------------------------
>  Seq Scan on sal_emp  (cost=0.00..21.00 rows=9 width=64)
>    Filter: (pay_by_quarter[1] = ANY ('{10000,2}'::integer[]))
> (2 rows)
>
> * if the left side of the operator expression node contains volatile
> functions, then don't do the transformation.
>
> I'm also not sure about the volatility check function, because we perform such a conversion at the parsing stage, and
atthis stage we don't have a RelOptInfo variable and especially a RestictInfo such as PathTarget. 
>
 see the example in here:
https://www.postgresql.org/message-id/CACJufxGXhJ823cdAdp2Ho7qC-HZ3_-dtdj-myaAi_u9RQLn45g%40mail.gmail.com

set enable_or_transformation to on;
create or replace function retint(int) returns int as
$func$
begin raise notice 'hello';
        return $1 + round(10 * random()); end
$func$ LANGUAGE plpgsql;

SELECT count(*) FROM tenk1 WHERE thousand = 42;
will return 10 rows.

SELECT count(*) FROM tenk1 WHERE thousand = 42 AND (retint(1) = 4 OR
retint(1) = 3);
this query I should return 20 notices 'hello', but now only 10.

EXPLAIN (COSTS OFF)
SELECT count(*) FROM tenk1
WHERE thousand = 42 AND (retint(1) = 4 OR  retint(1) = 3);
                                  QUERY PLAN
------------------------------------------------------------------------------
 Aggregate
   ->  Seq Scan on tenk1
         Filter: ((thousand = 42) AND (retint(1) = ANY ('{4,3}'::integer[])))
(3 rows)