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https://issues.apache.org/jira/browse/TAJO-1130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14395664#comment-14395664
 ] 

ASF GitHub Bot commented on TAJO-1130:
--------------------------------------

Github user jihoonson commented on the pull request:

    https://github.com/apache/tajo/pull/423#issuecomment-89546614
  
    I run a test with TPC-H Q10, and found a problem of the wrong query result.
    Please see the following.
    ```
    default> \set QUERY_EXECUTE_PARALLEL 1
    default> select count(*) from (select c_custkey, c_name, 
sum(l_extendedprice * (1 - l_discount)) as revenue, c_acctbal, n_name, 
c_address, c_phone, c_comment from customer as c join nation as n on 
c.c_nationkey = n.n_nationkey join orders as o on c.c_custkey = o.o_custkey and 
o.o_orderdate >= '1993-10-01' and o.o_orderdate < '1994-01-01' join lineitem as 
l on l.l_orderkey = o.o_orderkey and l.l_returnflag = 'R' group by c_custkey, 
c_name, c_acctbal, c_phone, n_name, c_address, c_comment order by revenue desc) 
t;
    Progress: 16%, response time: 2.185 sec
    Progress: 16%, response time: 2.186 sec
    Progress: 16%, response time: 2.588 sec
    Progress: 16%, response time: 3.394 sec
    Progress: 37%, response time: 4.399 sec
    Progress: 100%, response time: 4.946 sec
    ?count
    -------------------------------
    37967
    (1 rows, 4.946 sec, 6 B selected)
    default> \set QUERY_EXECUTE_PARALLEL 3
    default> select count(*) from (select c_custkey, c_name, 
sum(l_extendedprice * (1 - l_discount)) as revenue, c_acctbal, n_name, 
c_address, c_phone, c_comment from customer as c join nation as n on 
c.c_nationkey = n.n_nationkey join orders as o on c.c_custkey = o.o_custkey and 
o.o_orderdate >= '1993-10-01' and o.o_orderdate < '1994-01-01' join lineitem as 
l on l.l_orderkey = o.o_orderkey and l.l_returnflag = 'R' group by c_custkey, 
c_name, c_acctbal, c_phone, n_name, c_address, c_comment order by revenue desc) 
t;
    Progress: 25%, response time: 1.627 sec
    Progress: 25%, response time: 1.628 sec
    Progress: 25%, response time: 2.034 sec
    Progress: 25%, response time: 2.837 sec
    Progress: 35%, response time: 3.841 sec
    Progress: 100%, response time: 4.398 sec
    ?count
    -------------------------------
    1159
    (1 rows, 4.398 sec, 5 B selected)
    ```


> Concurrent execution of independent execution blocks 
> -----------------------------------------------------
>
>                 Key: TAJO-1130
>                 URL: https://issues.apache.org/jira/browse/TAJO-1130
>             Project: Tajo
>          Issue Type: Improvement
>          Components: query master
>            Reporter: Jihoon Son
>            Assignee: Navis
>
> Currently, Tajo can execute ExecutionBlocks one by one even though there 
> remain enough resources to execute two or more ExecutionBlocks.
> We can improve the query processing performance by executing two or more 
> independent ExecutionBlocks if possible.



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