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From "Vladimir Ozerov (JIRA)" <j...@apache.org>
Subject [jira] [Created] (IGNITE-8732) SQL: REPLICATED cache cannot be left-joined to PARTITIONED
Date Thu, 07 Jun 2018 09:44:00 GMT
Vladimir Ozerov created IGNITE-8732:
---------------------------------------

             Summary: SQL: REPLICATED cache cannot be left-joined to PARTITIONED
                 Key: IGNITE-8732
                 URL: https://issues.apache.org/jira/browse/IGNITE-8732
             Project: Ignite
          Issue Type: Bug
          Components: sql
    Affects Versions: 2.5
            Reporter: Vladimir Ozerov


*Steps to reproduce*
# Run {{org.apache.ignite.sqltests.ReplicatedSqlTest#testLeftJoinReplicatedPartitioned}}
# Observe that we have 2x results on 2-node cluster

*Root Cause*
{{left LEFT JOIN right ON cond}} operation assumes full scan of of a left expression. Currently
we perform this scan on every node and then simply merge results on reducer. Two nodes, two
scans of {{REPLICATED}} cache, 2x results.

*Solution*
We may consider several solutions. Deeper analysis is required to understand which is the
right one.

# Perform deduplication on reducer
# Treat {{REPLICATED}} cache as {{PARTITIONED}}. Essentially, we just need to pass proper
backup filter. But what if {{REPLICATED}} cache spans more nodes than {{PARTITIONED}}? We
cannot rely on primary/backup in this case
# Implement additional execution phase as follows: 
{code}
SELECT left.cols, right.cols FROM left INNER JOIN right ON cond; // Get common part
UNION
SELECT left.cols, [NULL].cols FROM left WHERE left.id NOT IN ([ids from the first phase])
{code}




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