Aleksey Plekhanov created IGNITE-20383:
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Summary: Calcite engine. Convert one input of a join to the
broadcast distribution
Key: IGNITE-20383
URL: https://issues.apache.org/jira/browse/IGNITE-20383
Project: Ignite
Issue Type: Improvement
Reporter: Aleksey Plekhanov
Assignee: Aleksey Plekhanov
Sometimes, if join inputs are not collocated it's worth to broadcast one of the
inputs, for example, query:
{code:sql}
SELECT * FROM emps WHERE emps.salary = (SELECT AVG(emps.salary) FROM emps){code}
Currently has plan:
{noformat}
IgniteProject(ID=[$0], NAME=[$1], SALARY=[$2])
IgniteNestedLoopJoin(condition=[=($2, $3)], joinType=[inner])
IgniteExchange(distribution=[single])
IgniteTableScan(table=[[PUBLIC, EMPS]])
IgniteReduceHashAggregate(group=[{}], AVG(EMPS.SALARY)=[AVG($0)])
IgniteExchange(distribution=[single])
IgniteMapHashAggregate(group=[{}], AVG(EMPS.SALARY)=[AVG($0)])
IgniteIndexScan(table=[[PUBLIC, EMPS]], index=[TST],
requiredColumns=[{2}], collation=[[2 ASC-nulls-first]])
{noformat}
But this plan is not optimal, since we should send entire table EMP from all
nodes to the single node. For such a query it's better to broadcast result of
the aggregation, in this case plan will be something like:
{noformat}
IgniteExchange(distribution=[single])
IgniteProject(ID=[$0], NAME=[$1], SALARY=[$2])
IgniteCorrelatedNestedLoopJoin(...)
IgniteExchange(distribution=[broadcast])
IgniteReduceHashAggregate(group=[{}], AVG(EMPS.SALARY)=[AVG($0)])
IgniteExchange(distribution=[single])
IgniteMapHashAggregate(group=[{}], AVG(EMPS.SALARY)=[AVG($0)])
IgniteIndexScan(table=[[PUBLIC, EMPS]], index=[SALARY_IDX])
IgniteIndexScan(table=[[PUBLIC, EMPS]], index=[SALARY_IDX])
{noformat}
But currently we don't try to convert any of the join inputs to the broadcast
distribution. We should try to do this.
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