[DRILL-3716] Drill should push filter past aggregate in order to improve query performance.

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.2.0
• Component/s: Query Planning & Optimization
• Assignee: Jinfeng Ni
• Reporter: Jinfeng Ni
• Created: 27/Aug/15 16:37
• Updated: 18/Sep/15 16:30
• Resolved: 27/Aug/15 17:46

Description

For the following query which has a filter on top of an aggregation, Drill's currently push the filter pass through the aggregation. As a result, we may miss some optimization opportunity. For instance, such filter could potentially been pushed into scan if it qualifies for partition pruning.

For the following query:

select n_regionkey, cnt from 
     (select n_regionkey, count(*) cnt 
      from (select n.n_nationkey, n.n_regionkey, n.n_name 
               from cp.`tpch/nation.parquet` n 
                  left join 
                       cp.`tpch/region.parquet` r 
                on n.n_regionkey = r.r_regionkey) 
       group by n_regionkey) 
where n_regionkey = 2;

The current plan shows a filter (00-04) on top of aggregation(00-05). The better plan would have the filter pushed pass the aggregation.

The root cause of this problem is Drill's ruleset does not include FilterAggregateTransoposeRule from Calcite library.

00-01      Project(n_regionkey=[$0], cnt=[$1])
00-02        Project(n_regionkey=[$0], cnt=[$1])
00-03          SelectionVectorRemover
00-04            Filter(condition=[=($0, 2)])
00-05              StreamAgg(group=[{0}], cnt=[COUNT()])
00-06                Project(n_regionkey=[$0])
00-07                  MergeJoin(condition=[=($0, $1)], joinType=[left])
00-09                    SelectionVectorRemover
00-11                      Sort(sort0=[$0], dir0=[ASC])
00-13                        Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath [path=classpath:/tpch/nation.parquet]], selectionRoot=classpath:/tpch/nation.parquet, numFiles=1, columns=[`n_regionkey`]]])
00-08                    SelectionVectorRemover
00-10                      Sort(sort0=[$0], dir0=[ASC])
00-12                        Scan(groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath [path=classpath:/tpch/region.parquet]], selectionRoot=classpath:/tpch/region.parquet, numFiles=1, columns=[`r_regionkey`]]])

Issue Links

• is duplicated by: DRILL-2748 Filter is not pushed down into subquery with the group by