[HIVE-15493] Wrong result for LEFT outer join in Tez using MapJoinOperator

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.2.0
• Fix Version/s: 2.2.0
• Assignee: Jesús Camacho Rodríguez
• Reporter: Jesús Camacho Rodríguez
• Created: 22/Dec/16 00:31
• Updated: 27/Feb/24 22:24
• Resolved: 29/Dec/16 20:56

Description

To reproduce, we can run in Tez:

set hive.auto.convert.join=true;

DROP TABLE IF EXISTS test_1; 
CREATE TABLE test_1 
( 
member BIGINT 
, age VARCHAR (100) 
) 
STORED AS TEXTFILE 
; 

DROP TABLE IF EXISTS test_2; 
CREATE TABLE test_2 
( 
member BIGINT 
) 
STORED AS TEXTFILE 
; 

INSERT INTO test_1 VALUES (1, '20'), (2, '30'), (3, '40'); 
INSERT INTO test_2 VALUES (1), (2), (3); 

SELECT 
t2.member 
, t1.age_1 
, t1.age_2 
FROM 
test_2 t2 
LEFT JOIN ( 
SELECT 
member 
, age as age_1 
, age as age_2 
FROM 
test_1 
) t1 
ON t2.member = t1.member 
;

Result is:

1	20	NULL
3	40	NULL
2	30	NULL

Correct result is:

1	20	20
3	40	40
2	30	30

Bug was introduced by HIVE-10582. Though the fix in HIVE-10582 does not contain tests, it does look legit. In fact, the problem seems to be in the MapJoinOperator itself. It only happens for LEFT outer join (not with RIGHT outer or FULL outer). Although I am still trying to understand part of the MapJoinOperator code path, the bug could be in the initialization of the operator. It only happens when we have duplicate values in the right part of the output.

Till we have more time to study the problem in detail and fix the MapJoinOperator, I will submit a fix that removes the code in SemanticAnalyzer that reuses duplicated value expressions from RS to create multiple columns in the join output (this is equivalent to reverting HIVE-10582).

Once this is pushed, I will create a follow-up issue to take this code back and tackle the problem in the MapJoinOperator.

Issue Links

• is related to: HIVE-15524 Wrong result for LEFT outer join in Tez using MapJoinOperator