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@xxxxxxxxxxxx>
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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