org.apache.spark.sql.connector.read

Interface SupportsPushDownAggregates

All Superinterfaces:

ScanBuilder

@Evolving
public interface SupportsPushDownAggregates
extends ScanBuilder

A mix-in interface for ScanBuilder. Data sources can implement this interface to push down aggregates.

If the data source can't fully complete the grouping work, then supportCompletePushDown(Aggregation) should return false, and Spark will group the data source output again. For queries like "SELECT min(value) AS m FROM t GROUP BY key", after pushing down the aggregate to the data source, the data source can still output data with duplicated keys, which is OK as Spark will do GROUP BY key again. The final query plan can be something like this:

   Aggregate [key#1], [min(min_value#2) AS m#3]
     +- RelationV2[key#1, min_value#2]
 

Similarly, if there is no grouping expression, the data source can still output more than one rows.

When pushing down operators, Spark pushes down filters to the data source first, then push down aggregates or apply column pruning. Depends on data source implementation, aggregates may or may not be able to be pushed down with filters. If pushed filters still need to be evaluated after scanning, aggregates can't be pushed down.

Since:

3.2.0

Method Summary

Modifier and Type	Method and Description
boolean	pushAggregation(Aggregation aggregation) Pushes down Aggregation to datasource.
default boolean	supportCompletePushDown(Aggregation aggregation) Whether the datasource support complete aggregation push-down.

Methods inherited from interface org.apache.spark.sql.connector.read.ScanBuilder

build

Method Detail

supportCompletePushDown

default boolean supportCompletePushDown(Aggregation aggregation)

Whether the datasource support complete aggregation push-down. Spark will do grouping again if this method returns false.

Parameters:

aggregation - Aggregation in SQL statement.

Returns:

true if the aggregation can be pushed down to datasource completely, false otherwise.

pushAggregation

boolean pushAggregation(Aggregation aggregation)

Pushes down Aggregation to datasource. The order of the datasource scan output columns should be: grouping columns, aggregate columns (in the same order as the aggregate functions in the given Aggregation).

Parameters:

aggregation - Aggregation in SQL statement.

Returns:

true if the aggregation can be pushed down to datasource, false otherwise.