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From "Rahul Challapalli (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-5148) Replace hash-distribution with a simple round-robin distribution for a simple order by query
Date Wed, 21 Dec 2016 21:37:58 GMT
Rahul Challapalli created DRILL-5148:
----------------------------------------

             Summary: Replace hash-distribution with a simple round-robin distribution for
a simple order by query
                 Key: DRILL-5148
                 URL: https://issues.apache.org/jira/browse/DRILL-5148
             Project: Apache Drill
          Issue Type: Bug
          Components: Execution - Relational Operators, Query Planning & Optimization
    Affects Versions: 1.10.0
            Reporter: Rahul Challapalli


git.commit.id.abbrev=cf2b7c7

The below plan indicates that we use hash-distribution to avoid data skew. However in the
below case a simple round-robin approach would be sufficient

{code}
explain plan for select * from dfs.`/drill/testdata/resource-manager/5kwidecolumns_500k.tbl`
order by columns[0];
+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      Project(*=[$0])
00-02        Project(T2¦¦*=[$0])
00-03          SingleMergeExchange(sort0=[1 ASC])
01-01            SelectionVectorRemover
01-02              Sort(sort0=[$1], dir0=[ASC])
01-03                Project(T2¦¦*=[$0], EXPR$1=[$1])
01-04                  HashToRandomExchange(dist0=[[$1]])
02-01                    UnorderedMuxExchange
03-01                      Project(T2¦¦*=[$0], EXPR$1=[$1], E_X_P_R_H_A_S_H_F_I_E_L_D=[hash32AsDouble($1)])
03-02                        Project(T2¦¦*=[$0], EXPR$1=[ITEM($1, 0)])
03-03                          Project(T2¦¦*=[$0], columns=[$1])
03-04                            Scan(groupscan=[EasyGroupScan [selectionRoot=maprfs:/drill/testdata/resource-manager/5kwidecolumns_500k.tbl,
numFiles=1, columns=[`*`], files=[maprfs:///drill/testdata/resource-manager/5kwidecolumns_500k.tbl]]])
{code}



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