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https://issues.apache.org/jira/browse/DRILL-1846?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14243404#comment-14243404
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Aman Sinha commented on DRILL-1846:
-----------------------------------
Here's the plan. Note the SingleMergeExchange operator 02-02 expects the
output degree of parallelism to be exactly 1. However, it appears that when we
determine the parallelism for fragment 02 we use a higher value.
{code}
0: jdbc:drill:zk=local> explain plan for select n_nationkey from (select
n_nationkey, n_regionkey from cp.`tpch/nation.parquet` order by n_regionkey) n
order by n.n_nationkey;
+------------+------------+
| text | json |
+------------+------------+
| 00-00 Screen
00-01 SingleMergeExchange(sort0=[0 ASC])
01-01 SelectionVectorRemover
01-02 Sort(sort0=[$0], dir0=[ASC])
01-03 HashToRandomExchange(dist0=[[$0]])
02-01 Project(n_nationkey=[$0])
02-02 SingleMergeExchange(sort0=[1 ASC])
03-01 SelectionVectorRemover
03-02 Sort(sort0=[$1], dir0=[ASC])
03-03 HashToRandomExchange(dist0=[[$1]])
04-01 Project(n_nationkey=[$1], n_regionkey=[$0])
04-02 Scan(groupscan=[ParquetGroupScan
[entries=[ReadEntryWithPath [path=/tpch/nation.parquet]],
selectionRoot=/tpch/nation.parquet, numFiles=1, columns=[`n_nationkey`,
`n_regionkey`]]])
{code}
> Re-ordering output of a subquery on a different column causes error
> -------------------------------------------------------------------
>
> Key: DRILL-1846
> URL: https://issues.apache.org/jira/browse/DRILL-1846
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Aman Sinha
> Assignee: Aman Sinha
>
> In the following the subquery does an order by on n_regionkey and the outer
> query does another order-by on n_nationkey. I have to set the slice_target =
> 1 for this particular data set but for the general case it is not needed.
> This query errors out:
> {code}
> alter session set `planner.slice_target` = 1
> select n.n_nationkey
> from (select n_nationkey, n_regionkey from cp.`tpch/nation.parquet`
> order by n_regionkey) n
> order by n.n_nationkey;
> Query failed: Query failed: Unexpected exception during fragment
> initialization: SingleMergeExchange only supports a single receiver endpoint
> {code}
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