Package org.apache.druid.query.topn

Class AggregateTopNMetricFirstAlgorithm

java.lang.Object

org.apache.druid.query.topn.AggregateTopNMetricFirstAlgorithm

All Implemented Interfaces:

TopNAlgorithm<int[],TopNParams>

public class AggregateTopNMetricFirstAlgorithm
extends Object
implements TopNAlgorithm<int[],TopNParams>

This TopNAlgorithm is tailored to processing aggregates on high cardility columns which are likely to have larger result sets. Internally it uses a 2 phase approach to compute the top-n result using the PooledTopNAlgorithm for each phase. The first phase is to process the segment with only the order-by aggregator to compute which values constitute the top 'n' results. With this information, a actual result set is computed by a second run of the PooledTopNAlgorithm, this time with all aggregators, but only considering the values from the 'n' results to avoid performing any aggregations that would have been thrown away for results that didn't make the top-n.

Field Summary

Fields inherited from interface org.apache.druid.query.topn.TopNAlgorithm

EMPTY_ARRAY, INIT_POSITION_VALUE, SKIP_POSITION_VALUE

Constructor Summary

Constructors

Constructor	Description
AggregateTopNMetricFirstAlgorithm(StorageAdapter storageAdapter, TopNQuery query, NonBlockingPool<ByteBuffer> bufferPool)

Method Summary

Modifier and Type	Method	Description
void	cleanup(TopNParams params)
TopNParams	makeInitParams(ColumnSelectorPlus selectorPlus, Cursor cursor)
void	run(TopNParams params, TopNResultBuilder resultBuilder, int[] ints, TopNQueryMetrics queryMetrics)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AggregateTopNMetricFirstAlgorithm

public AggregateTopNMetricFirstAlgorithm(StorageAdapter storageAdapter,
                                         TopNQuery query,
                                         NonBlockingPool<ByteBuffer> bufferPool)

Method Detail

makeInitParams

public TopNParams makeInitParams(ColumnSelectorPlus selectorPlus,
                                 Cursor cursor)

Specified by:

makeInitParams in interface TopNAlgorithm<int[],TopNParams>

run

public void run(TopNParams params,
                TopNResultBuilder resultBuilder,
                int[] ints,
                @Nullable
                TopNQueryMetrics queryMetrics)

Specified by:

run in interface TopNAlgorithm<int[],TopNParams>

cleanup

public void cleanup(TopNParams params)

Specified by:

cleanup in interface TopNAlgorithm<int[],TopNParams>