ChooseBestMatchIndexQueryStrategy.java example

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geowave-master
package mil.nga.giat.geowave.adapter.vector.index;

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

import mil.nga.giat.geowave.core.index.ByteArrayId;
import mil.nga.giat.geowave.core.index.ByteArrayRange;
import mil.nga.giat.geowave.core.index.IndexUtils;
import mil.nga.giat.geowave.core.index.sfc.data.MultiDimensionalNumericData;
import mil.nga.giat.geowave.core.store.CloseableIterator;
import mil.nga.giat.geowave.core.store.adapter.statistics.DataStatistics;
import mil.nga.giat.geowave.core.store.adapter.statistics.RowRangeHistogramStatistics;
import mil.nga.giat.geowave.core.store.index.Index;
import mil.nga.giat.geowave.core.store.index.PrimaryIndex;
import mil.nga.giat.geowave.core.store.query.BasicQuery;
import mil.nga.giat.geowave.core.store.query.ConstraintsQuery;
import mil.nga.giat.geowave.core.store.util.DataStoreUtils;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.opengis.feature.simple.SimpleFeature;

public class ChooseBestMatchIndexQueryStrategy implements
		IndexQueryStrategySPI
{
	public static final String NAME = "Best Match";
	private final static Logger LOGGER = LoggerFactory.getLogger(ChooseBestMatchIndexQueryStrategy.class);

	@Override
	public String toString() {
		return NAME;
	}

	@Override
	public CloseableIterator<Index<?, ?>> getIndices(
			final Map<ByteArrayId, DataStatistics<SimpleFeature>> stats,
			final BasicQuery query,
			final PrimaryIndex[] indices ) {
		return new CloseableIterator<Index<?, ?>>() {
			PrimaryIndex nextIdx = null;
			boolean done = false;
			int i = 0;

			@Override
			public boolean hasNext() {
				long min = Long.MAX_VALUE;
				PrimaryIndex bestIdx = null;

				while (!done && i < indices.length) {
					nextIdx = (PrimaryIndex) indices[i++];
					if (nextIdx.getIndexStrategy().getOrderedDimensionDefinitions().length == 0) continue;
					final List<MultiDimensionalNumericData> constraints = query.getIndexConstraints(nextIdx
							.getIndexStrategy());
					if (!stats.containsKey(RowRangeHistogramStatistics.composeId(nextIdx.getId()))) {
						LOGGER
								.warn("Best Match Heuristic requires statistic RowRangeHistogramStatistics for each index to properly choose an index.");
					}

					if (IndexUtils.isFullTableScan(constraints)) {
						// keep this is as a default in case all indices
						// result in a full table scan
						if (bestIdx == null) {
							bestIdx = nextIdx;
						}
					}
					else {
						final List<ByteArrayRange> ranges = DataStoreUtils.constraintsToByteArrayRanges(
								constraints,
								nextIdx.getIndexStrategy(),
								ConstraintsQuery.MAX_RANGE_DECOMPOSITION);
						final long temp = DataStoreUtils.cardinality(
								nextIdx,
								stats,
								ranges);
						if (temp < min) {
							bestIdx = nextIdx;
							min = temp;
						}
					}

				}
				nextIdx = bestIdx;
				done = true;
				return nextIdx != null;
			}

			@Override
			public Index<?, ?> next()
					throws NoSuchElementException {
				if (nextIdx == null) {
					throw new NoSuchElementException();
				}
				final Index<?, ?> returnVal = nextIdx;
				nextIdx = null;
				return returnVal;
			}

			@Override
			public void remove() {}

			@Override
			public void close()
					throws IOException {}
		};
	}
}