[DRILL-7013] Hash-Join and Hash-Aggr to handle incoming with selection vectors

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 1.15.0
• Component/s: Execution - Relational Operators, Query Planning & Optimization
• Assignee: Unassigned
• Reporter: Boaz Ben-Zvi
• Created: 29/Jan/19 04:14
• Updated: 29/Jan/19 04:21

Description

  The Hash-Join and Hash-Aggr operators copy each incoming row separately. When the incoming data has a selection vector (e.g., outgoing from a Filter), a SelectionVectorRemover is added before the Hash operator, as the latter cannot handle the selection vector.  

  Thus every row is needlessly being copied twice!

Suggestion: Enhance the Hash operators to handle potential incoming selection vectors, thus eliminating  the need for the extra copy. The planner needs to be changed not to add that SelectionVectorRemover.

(Two comments:

• Note the special case of Hash-Join with num_partitions = 1, where the build side vectors are used as is, not copied.
• Conflicts with the suggestion not to copy probe vectors, in DRILL-5912 )
   

For example:

select * from cp.`tpch/lineitem.parquet` L,  cp.`tpch/orders.parquet` O where O.o_custkey > 1498 and L.l_orderkey > 58999 and O.o_orderkey = L.l_orderkey 

And the plan:

00-00 Screen : rowType = RecordType(DYNAMIC_STAR **, DYNAMIC_STAR **0):
00-01 ProjectAllowDup(=[$0], 0=[$1]) : rowType = RecordType(DYNAMIC_STAR , DYNAMIC_STAR 0):
00-02 Project(T44¦¦=[$0], T45¦¦=[$2]) : rowType = RecordType(DYNAMIC_STAR T44¦¦, DYNAMIC_STAR T45¦¦):
00-03 HashJoin(condition=[=($1, $4)], joinType=[inner], semi-join: =[false]) : rowType = RecordType(DYNAMIC_STAR T44¦¦, ANY l_orderkey, DYNAMIC_STAR T45¦¦, ANY o_custkey, ANY o_orderkey):
00-05 SelectionVectorRemover : rowType = RecordType(DYNAMIC_STAR T44¦¦, ANY l_orderkey):
00-07 Filter(condition=[>($1, 58999)]) : rowType = RecordType(DYNAMIC_STAR T44¦¦, ANY l_orderkey):
00-09 Project(T44¦¦=[$0], l_orderkey=[$1]) : rowType = RecordType(DYNAMIC_STAR T44¦¦, ANY l_orderkey):
00-11 Scan(table=[[cp, tpch/lineitem.parquet]], groupscan=[ParquetGroupScan [entries=[ReadEntryWithPath [path=classpath:/tpch/lineitem.parquet]],
00-04 SelectionVectorRemover : rowType = RecordType(DYNAMIC_STAR T45¦¦, ANY o_custkey, ANY o_orderkey):
00-06 Filter(condition=[AND(>($1, 1498), >($2, 58999))]) : rowType = RecordType(DYNAMIC_STAR T45¦¦, ANY o_custkey, ANY o_orderkey):
00-08 Project(T45¦¦**=[$0], o_custkey=[$1], o_orderkey=[$2]) : rowType = RecordType(DYNAMIC_STAR T45¦¦, ANY o_custkey, ANY o_orderkey):
00-10 Scan(table=[[cp, tpch/orders.parquet]],