CardinalityAggregatorFactory.java example

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package org.elasticsearch.search.aggregations.metrics.cardinality;

import org.elasticsearch.search.aggregations.Aggregator;
import org.elasticsearch.search.aggregations.bucket.SingleBucketAggregator;
import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
import org.elasticsearch.search.aggregations.support.AggregationContext;
import org.elasticsearch.search.aggregations.support.ValuesSource;
import org.elasticsearch.search.aggregations.support.ValuesSourceAggregatorFactory;
import org.elasticsearch.search.aggregations.support.ValuesSourceConfig;

import java.io.IOException;
import java.util.List;
import java.util.Map;

final class CardinalityAggregatorFactory extends ValuesSourceAggregatorFactory.LeafOnly<ValuesSource> {

    private final long precisionThreshold;

    CardinalityAggregatorFactory(String name, ValuesSourceConfig config, long precisionThreshold) {
        super(name, InternalCardinality.TYPE.name(), config);
        this.precisionThreshold = precisionThreshold;
    }

    private int precision(Aggregator parent) {
        return precisionThreshold < 0 ? defaultPrecision(parent) : HyperLogLogPlusPlus.precisionFromThreshold(precisionThreshold);
    }

    @Override
    protected Aggregator createUnmapped(AggregationContext context, Aggregator parent, List<PipelineAggregator> pipelineAggregators, Map<String, Object> metaData)
            throws IOException {
        return new CardinalityAggregator(name, null, precision(parent), config.formatter(), context, parent, pipelineAggregators, metaData);
    }

    @Override
    protected Aggregator doCreateInternal(ValuesSource valuesSource, AggregationContext context, Aggregator parent,
            boolean collectsFromSingleBucket, List<PipelineAggregator> pipelineAggregators, Map<String, Object> metaData) throws IOException {
        return new CardinalityAggregator(name, valuesSource, precision(parent), config.formatter(), context, parent, pipelineAggregators,
                metaData);
    }

    /*
     * If one of the parent aggregators is a MULTI_BUCKET one, we might want to lower the precision
     * because otherwise it might be memory-intensive. On the other hand, for top-level aggregators
     * we try to focus on accuracy.
     */
    private static int defaultPrecision(Aggregator parent) {
        int precision = HyperLogLogPlusPlus.DEFAULT_PRECISION;
        while (parent != null) {
            if (parent instanceof SingleBucketAggregator == false) {
                // if the parent creates buckets, we substract 5 to the precision,
                // which will effectively divide the memory usage of each counter by 32
                precision -= 5;
            }
            parent = parent.parent();
        }

        return Math.max(precision, HyperLogLogPlusPlus.MIN_PRECISION);
    }

}