Re: "JPPD bypassed: DISTINCT clause" in 19c

Hi Nenad,

Yes, JPPD doesn't work in case of table(), XMLTABLE and JSON_TABLE: http://orasql.org/2019/05/30/workarounds-for-jppd-with-view-and-tablekokbf-xmltable-or-json_table-functions/

On Fri, Sep 4, 2020 at 3:26 PM Noveljic Nenad <nenad.noveljic_at_vontobel.com> wrote:

> Believe it or not, JSON is the culprit. The problem is much more serious
> than initially reported. JSON entirely shuts off cost based JPPD in 19c!
>
>
>
> Find the queries below (the table definitions are from
> https://nenadnoveljic.com/blog/join-predicate-push-down-additional-phase/
> ):
>
>
>
> With distinct:
>
>
>
> explain plan for
>
> select /*+ qb_name(QB_MAIN) */
>
> JSON_OBJECT (
>
> 'id' VALUE 1
>
> RETURNING VARCHAR2 (10)
>
> STRICT)
>
> from t1 left outer join
>
> ( select /*+ qb_name(QB_MIDDLE) */ distinct t2.n2
>
> from
>
> t2 ,
>
> ( select /*+ qb_name(QB_INNER ) */ distinct t3.n2
>
> from t3, t4
>
> where t4.n1 = t3.n1
>
> ) v2
>
> where v2.n2(+) = t2.n1
>
> ) v1 on v1.n2 = t1.n1
>
> ;
>
>
>
> JPPD: JPPD bypassed: DISTINCT clause.
>
> JPPD: JPPD bypassed: DISTINCT clause.
>
>
>
> Without distinct:
>
>
>
> explain plan for
>
> select /*+ qb_name(QB_MAIN) */
>
> JSON_OBJECT (
>
> 'id' VALUE 1
>
> RETURNING VARCHAR2 (10)
>
> STRICT)
>
> from t1 left outer join
>
> ( select /*+ qb_name(QB_MIDDLE) */ t2.n2
>
> from
>
> t2 ,
>
> ( select /*+ qb_name(QB_INNER ) */ t3.n2
>
> from t3, t4
>
> where t4.n1 = t3.n1
>
> ) v2
>
> where v2.n2(+) = t2.n1
>
> ) v1 on v1.n2 = t1.n1
>
> ;
>
>
>
> JPPD: JPPD bypassed: View has unsupported constructs.
>
>
>
> Without JSON:
>
>
>
> explain plan for
>
> select /*+ qb_name(QB_MAIN) */
>
> 1
>
> from t1 left outer join
>
> ( select /*+ qb_name(QB_MIDDLE) */ t2.n2
>
> from
>
> t2 ,
>
> ( select /*+ qb_name(QB_INNER ) */ t3.n2
>
> from t3, t4
>
> where t4.n1 = t3.n1
>
> ) v2
>
> where v2.n2(+) = t2.n1
>
> ) v1 on v1.n2 = t1.n1
>
> ;
>
>
>
> JPPD: Considering Cost-based predicate pushdown from query block
> SEL$1A44BB0C (#1)
>
> Cost-based predicate pushdown (JPPD)
>
> JPPD: Checking validity of push-down in query block QB_MIDDLE (#2)
>
> JPPD: Checking validity of push-down from query block QB_MIDDLE (#2) to
> query block QB_INNER (#3)
>
> JPPD: Passed validity checks
>
> JPPD: JPPD: Pushdown from query block QB_MIDDLE (#2) passed validity
> checks.
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
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-- 
Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
Oracle ACE Associate
http://orasql.org

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