Aman Sinha created DRILL-885:
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Summary: Handle project pushdown for constant expressions
Key: DRILL-885
URL: https://issues.apache.org/jira/browse/DRILL-885
Project: Apache Drill
Issue Type: Bug
Reporter: Aman Sinha
In the following query, notice in the Explain plan that the node
Project($f0=[0]) is projecting a constant, so ideally we should not have to
produce a whole bunch of columns from either side of the join unless those
columns are needed for the join condition. However, currently we do produce
those unnecessary columns from the Scan below (see the Customer parquet scan on
the left side of the HashJoin). This hurts performance.
0: jdbc:drill:zk=local> explain plan for select count(*) from (select
c.c_custkey, c.c_name, c.c_address, c.c_nationkey, c.c_phone, c.c_acctbal,
c.c_mktsegment, c.c_comment, n.n_nationkey, n.n_name, n.n_nationkey,
n.n_comment from cp.`tpch/customer.parquet` c JOIN cp.`tpch/nation.parquet` n
ON (c.c_nationkey = n.n_nationkey));
+------------+------------+
| text | json |
+------------+------------+
| 00-00 Screen
00-01 StreamAgg(group=[{}], EXPR$0=[SUM($0)])
00-02 UnionExchange
01-01 StreamAgg(group=[{}], EXPR$0=[COUNT()])
01-02 Project($f0=[0])
01-03 HashJoin(condition=[=($1, $10)], joinType=[inner])
01-05 HashToRandomExchange(dist0=[[$1]])
02-01 Scan(groupscan=[ParquetGroupScan
[entries=[ReadEntryWithPath [path=/tpch/customer.parquet]],
selectionRoot=/tpch/customer.parquet, columns=[SchemaPath [`c_nationkey`],
SchemaPath [`c_custkey`], SchemaPath [`c_name`], SchemaPath [`c_address`],
SchemaPath [`c_phone`], SchemaPath [`c_acctbal`], SchemaPath [`c_mktsegment`],
SchemaPath [`c_comment`]]]])
01-04 Project(*0=[$0], n_nationkey=[$1], n_name=[$2],
n_comment=[$3])
01-06 HashToRandomExchange(dist0=[[$1]])
03-01 Scan(groupscan=[ParquetGroupScan
[entries=[ReadEntryWithPath [path=/tpch/nation.parquet]],
selectionRoot=/tpch/nation.parquet, columns=[SchemaPath [`n_nationkey`],
SchemaPath [`n_name`], SchemaPath [`n_comment`]]]])
Here's the Drill Logical plan for the same query:
| DrillScreenRel
DrillAggregateRel(group=[{}], EXPR$0=[COUNT()])
DrillProjectRel($f0=[0])
DrillJoinRel(condition=[=($1, $10)], joinType=[inner])
DrillScanRel(table=[[cp, tpch/customer.parquet]])
DrillScanRel(table=[[cp, tpch/nation.parquet]])
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