[jira] [Created] (IGNITE-20383) Calcite engine. Convert one input of a join to the broadcast distribution

["Aleksey Plekhanov (Jira)" <ji...@apache.org>]

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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