[jira] [Assigned] (IMPALA-8263) Planner failed to flip build/probe side of join

["Paul Rogers (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-8263?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Paul Rogers reassigned IMPALA-8263:
-----------------------------------

    Assignee:     (was: Paul Rogers)

> Planner failed to flip build/probe side of join
> -----------------------------------------------
>
>                 Key: IMPALA-8263
>                 URL: https://issues.apache.org/jira/browse/IMPALA-8263
>             Project: IMPALA
>          Issue Type: Bug
>          Components: Frontend
>    Affects Versions: Impala 3.1.0
>            Reporter: Paul Rogers
>            Priority: Major
>
> TPC-H query 8 was reviewed after applying the changes proposed for DRILL-8014. (See {{tpch-all.test}}.) The revised plan has better cardinality number, but contains this odd structure:
> {noformat}
> 11:HASH JOIN [INNER JOIN]
> |  hash predicates: o_custkey = c_custkey
> |  row-size=139B cardinality=39.66K
> |
> |--04:SCAN HDFS [tpch.customer]
> |     row-size=10B cardinality=150.00K
> |
> 10:HASH JOIN [INNER JOIN]
> |  hash predicates: o_orderkey = l_orderkey
> |  row-size=129B cardinality=39.66K
> {noformat}
> As I understand it, the planner should flip the left and right sides of an inner join if the right side (the 04 scan) has a larger cardinality than the left (join 10) side. That flip did not happen in this case, causing the join to build a hash table about 4 times larger than necessary.
> Perhaps there is some other constraint. Investigate to determine if the behavior is correct (and if so why), or the source of incorrect behavior.



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