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From "Hanumath Rao Maduri (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-6159) No need to offset rows if order by is not specified in the query.
Date Wed, 14 Feb 2018 22:48:00 GMT
Hanumath Rao Maduri created DRILL-6159:
------------------------------------------

             Summary: No need to offset rows if order by is not specified in the query.
                 Key: DRILL-6159
                 URL: https://issues.apache.org/jira/browse/DRILL-6159
             Project: Apache Drill
          Issue Type: Bug
          Components: Query Planning &amp; Optimization
    Affects Versions: 1.12.0
            Reporter: Hanumath Rao Maduri
            Assignee: Hanumath Rao Maduri
             Fix For: Future


For the queries which have offset and limit and no order by no need to add the offset to limit
during pushdown of the limit.

Sql doesn't guarantee order in the output if no order by is specified in the query. It is
observed that for the queries with offset and limit and no order by, current optimizer is
adding the offset and limit and limiting those many rows. Doing so will not early exit the
query.

Here is an example for a query.

{code}
select zz1,zz2,a11 from dfs.tmp.viewtmp limit 100000 offset 10000000


00-00    Screen : rowType = RecordType(ANY zz1, ANY zz2, ANY a11): rowcount = 1.01E7, cumulative
cost = {1.06048844E8 rows, 5.54015404E8 cpu, 0.0 io, 1.56569100288E11 network, 4.64926176E7
memory}, id = 787
00-01      Project(zz1=[$0], zz2=[$1], a11=[$2]) : rowType = RecordType(ANY zz1, ANY zz2,
ANY a11): rowcount = 1.01E7, cumulative cost = {1.05038844E8 rows, 5.53005404E8 cpu, 0.0 io,
1.56569100288E11 network, 4.64926176E7 memory}, id = 786
00-02        SelectionVectorRemover : rowType = RecordType(ANY zz1, ANY zz2, ANY a11): rowcount
= 1.01E7, cumulative cost = {1.05038844E8 rows, 5.53005404E8 cpu, 0.0 io, 1.56569100288E11
network, 4.64926176E7 memory}, id = 785
00-03          Limit(offset=[10000000], fetch=[100000]) : rowType = RecordType(ANY zz1, ANY
zz2, ANY a11): rowcount = 1.01E7, cumulative cost = {9.4938844E7 rows, 5.42905404E8 cpu, 0.0
io, 1.56569100288E11 network, 4.64926176E7 memory}, id = 784
00-04            UnionExchange : rowType = RecordType(ANY zz1, ANY zz2, ANY a11): rowcount
= 1.01E7, cumulative cost = {8.4838844E7 rows, 5.02505404E8 cpu, 0.0 io, 1.56569100288E11
network, 4.64926176E7 memory}, id = 783
01-01              SelectionVectorRemover : rowType = RecordType(ANY zz1, ANY zz2, ANY a11):
rowcount = 1.01E7, cumulative cost = {7.4738844E7 rows, 4.21705404E8 cpu, 0.0 io, 3.2460300288E10
network, 4.64926176E7 memory}, id = 782
01-02                Limit(fetch=[10100000]) : rowType = RecordType(ANY zz1, ANY zz2, ANY
a11): rowcount = 1.01E7, cumulative cost = {6.4638844E7 rows, 4.11605404E8 cpu, 0.0 io, 3.2460300288E10
network, 4.64926176E7 memory}, id = 781
01-03                  Project(zz1=[$0], zz2=[$2], a11=[$1]) : rowType = RecordType(ANY zz1,
ANY zz2, ANY a11): rowcount = 2.3306983E7, cumulative cost = {5.4538844E7 rows, 3.71205404E8
cpu, 0.0 io, 3.2460300288E10 network, 4.64926176E7 memory}, id = 780
01-04                    HashJoin(condition=[=($0, $2)], joinType=[left]) : rowType = RecordType(ANY
ZZ1, ANY A, ANY ZZ2): rowcount = 2.3306983E7, cumulative cost = {5.4538844E7 rows, 3.71205404E8
cpu, 0.0 io, 3.2460300288E10 network, 4.64926176E7 memory}, id = 779
01-06                      Scan(groupscan=[EasyGroupScan [selectionRoot=maprfs:/tmp/csvd1,
numFiles=3, columns=[`ZZ1`, `A`], files=[maprfs:/tmp/csvd1/D1111aamulti11random2.csv, maprfs:/tmp/csvd1/D1111aamulti11random21.csv,
maprfs:/tmp/csvd1/D1111aamulti11random211.csv]]]) : rowType = RecordType(ANY ZZ1, ANY A):
rowcount = 2.3306983E7, cumulative cost = {2.3306983E7 rows, 4.6613966E7 cpu, 0.0 io, 0.0
network, 0.0 memory}, id = 776
01-05                      BroadcastExchange : rowType = RecordType(ANY ZZ2): rowcount = 2641626.0,
cumulative cost = {5283252.0 rows, 2.3774634E7 cpu, 0.0 io, 3.2460300288E10 network, 0.0 memory},
id = 778
02-01                        Scan(groupscan=[EasyGroupScan [selectionRoot=maprfs:/tmp/csvd2,
numFiles=1, columns=[`ZZ2`], files=[maprfs:/tmp/csvd2/D222random2.csv]]]) : rowType = RecordType(ANY
ZZ2): rowcount = 2641626.0, cumulative cost = {2641626.0 rows, 2641626.0 cpu, 0.0 io, 0.0
network, 0.0 memory}, id = 777
{code}

The limit pushed down is  Limit(fetch=[10100000]) instead it should be  Limit(fetch=[100000])
 



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