Aman Sinha has posted comments on this change. ( http://gerrit.cloudera.org:8080/19682 )
Change subject: IMPALA-12006: Improve cardinality estimation for joins involving multiple conjuncts ...................................................................... Patch Set 3: (1 comment) http://gerrit.cloudera.org:8080/#/c/19682/3//COMMIT_MSG Commit Message: http://gerrit.cloudera.org:8080/#/c/19682/3//COMMIT_MSG@30 PS3, Line 30: consider per join hints but in a complex query (or a view that is > It might also be hard to tune the query option when the query has hundreds Yes, there are tradeoffs in both the query option approach and the hints approach. Join cardinality estimation is a hard problem and we do need to look at better ways of doing this in the future using learning models or other techniques. Of course, better stats will always help. In terms of hints, couple of things to point out: 1. In a lot of cases, the queries may come from a BI tool and are generated queries instead of hand written and users may not have control over setting the hints. 2. For views: CREATE VIEW v1 AS …. t1 inner join t2 on a1 = a2 AND b1 = b2 q1: select * from v1 WHERE <predicate p1> q2: select * from v1 WHERE <predicate p2> The predicates p1, p2 may be pushed down below the join/one side of the join or both sides .. also the behavior of pushdown depends on inner vs outer joins. The static hints at the join level level will not be aware of such transformations. We could use both the query option and hints for more flexibility. -- To view, visit http://gerrit.cloudera.org:8080/19682 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: Impala-ASF Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: I845d778a58404af834f7501fc8157a5a4b4bcc35 Gerrit-Change-Number: 19682 Gerrit-PatchSet: 3 Gerrit-Owner: Aman Sinha <[email protected]> Gerrit-Reviewer: Aman Sinha <[email protected]> Gerrit-Reviewer: Csaba Ringhofer <[email protected]> Gerrit-Reviewer: Impala Public Jenkins <[email protected]> Gerrit-Reviewer: Kurt Deschler <[email protected]> Gerrit-Reviewer: Quanlong Huang <[email protected]> Gerrit-Comment-Date: Fri, 07 Apr 2023 03:42:30 +0000 Gerrit-HasComments: Yes
