Boaz Ben-Zvi created DRILL-7043:
-----------------------------------
Summary: Enhance Merge-Join to support Full Outer Join
Key: DRILL-7043
URL: https://issues.apache.org/jira/browse/DRILL-7043
Project: Apache Drill
Issue Type: Improvement
Components: Execution - Relational Operators, Query Planning &
Optimization
Affects Versions: 1.15.0
Reporter: Boaz Ben-Zvi
Assignee: Boaz Ben-Zvi
Currently the Merge Join operator internally cannot support a Right Outer
Join (and thus a Full Outer Join; for ROJ alone, the planner rotates the inputs
and specifies a Left Outer Join).
The actual reason for not supporting ROJ is the current MJ implementation -
when a match is found, it puts a mark on the right side and iterates down on
the right, resetting back at the end (and on to the next left side entry).
This would create an ambiguity if the next left entry is bigger than the
previous - is this an unmatched (i.e., need to return the right entry), or
there was a prior match (i.e., just advance to the next right).
Seems that adding a relevant flag to the persisted state ({{status}}) and
some other code changes would make the operator support Right-Outer-Join as
well (and thus a Full Outer Join). The planner need an update as well - to
suggest the MJ in case of a FOJ, and maybe not to rotate the inputs in some MJ
cases.
Currently trying a FOJ with MJ (i.e. HJ disabled) produces the following "no
plan found" from Calcite:
{noformat}
0: jdbc:drill:zk=local> select * from temp t1 full outer join temp2 t2 on
t1.d_date = t2.d_date;
Error: SYSTEM ERROR: CannotPlanException: Node
[rel#2804:Subset#8.PHYSICAL.SINGLETON([]).[]] could not be implemented; planner
state:
Root: rel#2804:Subset#8.PHYSICAL.SINGLETON([]).[]
Original rel:
DrillScreenRel(subset=[rel#2804:Subset#8.PHYSICAL.SINGLETON([]).[]]): rowcount
= 6.0, cumulative cost = {0.6000000000000001 rows, 0.6000000000000001 cpu, 0.0
io, 0.0 network, 0.0 memory}, id = 2802
DrillProjectRel(subset=[rel#2801:Subset#7.LOGICAL.ANY([]).[]], **=[$0],
**0=[$2]): rowcount = 6.0, cumulative cost = {6.0 rows, 12.0 cpu, 0.0 io, 0.0
network, 0.0 memory}, id = 2800
DrillJoinRel(subset=[rel#2799:Subset#6.LOGICAL.ANY([]).[]],
condition=[=($1, $3)], joinType=[full]): rowcount = 6.0, cumulative cost =
{10.0 rows, 104.0 cpu, 0.0 io, 0.0 network, 70.4 memory}, id = 2798
{noformat}
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
