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https://issues.apache.org/jira/browse/HIVE-4506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13650371#comment-13650371
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Lianhui Wang commented on HIVE-4506:
Fern, can you provide your sql?
if these tables used the same column in join clause, it used one mr.
example:
explain
SELECT /*+mapjoin(src2,src3)*/ src1.key, src3.value FROM src src1 JOIN src src2
ON (src1.key = src2.key) JOIN src src3 ON (src1.key = src3.key);
use one map reduce to join multiple small tables
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Key: HIVE-4506
URL: https://issues.apache.org/jira/browse/HIVE-4506
Project: Hive
Issue Type: Wish
Affects Versions: 0.10.0
Reporter: Fern
Priority: Minor
I know we can use map side join for small table.
by my test, if I use HQL like this
--
select /*+mapjoin(b,c)*/...
from a
left join b
on ...
left join c
on ...
---
b and c are both small tables, I expect do the join in one map reduce using
map side join. Actually, it would generate two map-reduce jobs by sequence.
Sorry, currently I am just a user of hive and not dig into the code, so this
is what I expect but I have no idea about how to improve now.
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