AggregateOptimizer

java.lang.Object
- simpledb.parallel.ParallelQueryPlanOptimizer
- - simpledb.parallel.AggregateOptimizer

```
public class AggregateOptimizer
extends ParallelQueryPlanOptimizer
```
Optimize aggregate operators of a parallel queryplan. Each aggregate operator within an un-optimized parallel query plan will be replaced by two aggregate operators, a down-stream aggregate operator and an up-stream aggregate operator. For example, max(column) will be replace by max(column) -> (shuffle/collect) -> max(column) In this way, the amount of data that need to be transmitted though network will be minimized.

Field Summary
- Fields inherited from class simpledb.parallel.ParallelQueryPlanOptimizer
  next

Constructors
Constructor and Description
`AggregateOptimizer()`
`AggregateOptimizer(ParallelQueryPlanOptimizer next)`

Methods
Modifier and Type	Method and Description
`protected void`	`doMyOptimization(TransactionId tid, ParallelQueryPlan plan)` Sub classes should implement this method to do the actual optimization
`protected DbIterator`	`parallelizeAggregate(DbIterator root)` Replace the aggregate operators in the local query plan with parallelized aggregate

Methods inherited from class simpledb.parallel.ParallelQueryPlanOptimizer
optimize

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Class AggregateOptimizer