Paul Rogers created IMPALA-8263:
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Summary: 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
Assignee: Paul Rogers
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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