Star Tree Implementation [OnHeap] (opensearch-project#14512)

---------
Signed-off-by: Sarthak Aggarwal <sarthagg@amazon.com>
Signed-off-by: Kaushal Kumar <ravi.kaushal97@gmail.com>

server/src/main/java/org/opensearch/index/codec/composite/Composite99DocValuesWriter.java

@@ -14,6 +14,7 @@
 import org.apache.lucene.index.MergeState;
 import org.apache.lucene.index.SegmentWriteState;
 import org.opensearch.common.annotation.ExperimentalApi;
+import org.opensearch.index.compositeindex.datacube.startree.builder.StarTreesBuilder;
 import org.opensearch.index.mapper.CompositeMappedFieldType;
 import org.opensearch.index.mapper.MapperService;
 import org.opensearch.index.mapper.StarTreeMapper;
@@ -98,7 +99,9 @@ private void createCompositeIndicesIfPossible(DocValuesProducer valuesProducer,
         if (compositeFieldSet.isEmpty()) {
             for (CompositeMappedFieldType mappedType : compositeMappedFieldTypes) {
                 if (mappedType instanceof StarTreeMapper.StarTreeFieldType) {
-                    // TODO : Call StarTree builder
+                    try (StarTreesBuilder starTreesBuilder = new StarTreesBuilder(fieldProducerMap, state, mapperService)) {
+                        starTreesBuilder.build();
+                    }
                 }
             }
         }

server/src/main/java/org/opensearch/index/compositeindex/datacube/startree/StarTreeDocument.java

@@ -0,0 +1,34 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.index.compositeindex.datacube.startree;
+
+import org.opensearch.common.annotation.ExperimentalApi;
+
+import java.util.Arrays;
+
+/**
+ * Star tree document
+ *
+ * @opensearch.experimental
+ */
+@ExperimentalApi
+public class StarTreeDocument {
+    public final Long[] dimensions;
+    public final Object[] metrics;
+
+    public StarTreeDocument(Long[] dimensions, Object[] metrics) {
+        this.dimensions = dimensions;
+        this.metrics = metrics;
+    }
+
+    @Override
+    public String toString() {
+        return Arrays.toString(dimensions) + " | " + Arrays.toString(metrics);
+    }
+}

server/src/main/java/org/opensearch/index/compositeindex/datacube/startree/aggregators/CountValueAggregator.java

@@ -0,0 +1,66 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+package org.opensearch.index.compositeindex.datacube.startree.aggregators;
+
+import org.opensearch.index.compositeindex.datacube.MetricStat;
+import org.opensearch.index.compositeindex.datacube.startree.aggregators.numerictype.StarTreeNumericType;
+
+/**
+ * Count value aggregator for star tree
+ *
+ * @opensearch.experimental
+ */
+public class CountValueAggregator implements ValueAggregator<Long> {
+    public static final StarTreeNumericType VALUE_AGGREGATOR_TYPE = StarTreeNumericType.LONG;
+    public static final long DEFAULT_INITIAL_VALUE = 1L;
+
+    @Override
+    public MetricStat getAggregationType() {
+        return MetricStat.COUNT;
+    }
+
+    @Override
+    public StarTreeNumericType getAggregatedValueType() {
+        return VALUE_AGGREGATOR_TYPE;
+    }
+
+    @Override
+    public Long getInitialAggregatedValueForSegmentDocValue(Long segmentDocValue, StarTreeNumericType starTreeNumericType) {
+        return DEFAULT_INITIAL_VALUE;
+    }
+
+    @Override
+    public Long mergeAggregatedValueAndSegmentValue(Long value, Long segmentDocValue, StarTreeNumericType starTreeNumericType) {
+        return value + 1;
+    }
+
+    @Override
+    public Long mergeAggregatedValues(Long value, Long aggregatedValue) {
+        return value + aggregatedValue;
+    }
+
+    @Override
+    public Long getInitialAggregatedValue(Long value) {
+        return value;
+    }
+
+    @Override
+    public int getMaxAggregatedValueByteSize() {
+        return Long.BYTES;
+    }
+
+    @Override
+    public Long toLongValue(Long value) {
+        return value;
+    }
+
+    @Override
+    public Long toStarTreeNumericTypeValue(Long value, StarTreeNumericType type) {
+        return value;
+    }
+}

server/src/main/java/org/opensearch/index/compositeindex/datacube/startree/aggregators/MetricAggregatorInfo.java

@@ -0,0 +1,130 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+package org.opensearch.index.compositeindex.datacube.startree.aggregators;
+
+import org.opensearch.index.compositeindex.datacube.MetricStat;
+import org.opensearch.index.compositeindex.datacube.startree.aggregators.numerictype.StarTreeNumericType;
+import org.opensearch.index.compositeindex.datacube.startree.utils.SequentialDocValuesIterator;
+import org.opensearch.index.fielddata.IndexNumericFieldData;
+
+import java.util.Comparator;
+import java.util.Objects;
+
+/**
+ * Builds aggregation function and doc values field pair to support various aggregations
+ *
+ * @opensearch.experimental
+ */
+public class MetricAggregatorInfo implements Comparable<MetricAggregatorInfo> {
+
+    public static final String DELIMITER = "_";
+    private final String metric;
+    private final String starFieldName;
+    private final MetricStat metricStat;
+    private final String field;
+    private final ValueAggregator valueAggregators;
+    private final StarTreeNumericType starTreeNumericType;
+    private final SequentialDocValuesIterator metricStatReader;
+
+    /**
+     * Constructor for MetricAggregatorInfo
+     */
+    public MetricAggregatorInfo(
+        MetricStat metricStat,
+        String field,
+        String starFieldName,
+        IndexNumericFieldData.NumericType numericType,
+        SequentialDocValuesIterator metricStatReader
+    ) {
+        this.metricStat = metricStat;
+        this.valueAggregators = ValueAggregatorFactory.getValueAggregator(metricStat);
+        this.starTreeNumericType = StarTreeNumericType.fromNumericType(numericType);
+        this.metricStatReader = metricStatReader;
+        this.field = field;
+        this.starFieldName = starFieldName;
+        this.metric = toFieldName();
+    }
+
+    /**
+     * @return metric type
+     */
+    public MetricStat getMetricStat() {
+        return metricStat;
+    }
+
+    /**
+     * @return field Name
+     */
+    public String getField() {
+        return field;
+    }
+
+    /**
+     * @return the metric stat name
+     */
+    public String getMetric() {
+        return metric;
+    }
+
+    /**
+     * @return aggregator for the field value
+     */
+    public ValueAggregator getValueAggregators() {
+        return valueAggregators;
+    }
+
+    /**
+     * @return star tree aggregated value type
+     */
+    public StarTreeNumericType getAggregatedValueType() {
+        return starTreeNumericType;
+    }
+
+    /**
+     * @return metric value reader iterator
+     */
+    public SequentialDocValuesIterator getMetricStatReader() {
+        return metricStatReader;
+    }
+
+    /**
+     * @return field name with metric type and field
+     */
+    public String toFieldName() {
+        return starFieldName + DELIMITER + field + DELIMITER + metricStat.getTypeName();
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(toFieldName());
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj instanceof MetricAggregatorInfo) {
+            MetricAggregatorInfo anotherPair = (MetricAggregatorInfo) obj;
+            return metricStat == anotherPair.metricStat && field.equals(anotherPair.field);
+        }
+        return false;
+    }
+
+    @Override
+    public String toString() {
+        return toFieldName();
+    }
+
+    @Override
+    public int compareTo(MetricAggregatorInfo other) {
+        return Comparator.comparing((MetricAggregatorInfo o) -> o.field)
+            .thenComparing((MetricAggregatorInfo o) -> o.metricStat)
+            .compare(this, other);
+    }
+}

server/src/main/java/org/opensearch/index/compositeindex/datacube/startree/aggregators/SumValueAggregator.java

@@ -0,0 +1,97 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+package org.opensearch.index.compositeindex.datacube.startree.aggregators;
+
+import org.apache.lucene.util.NumericUtils;
+import org.opensearch.index.compositeindex.datacube.MetricStat;
+import org.opensearch.index.compositeindex.datacube.startree.aggregators.numerictype.StarTreeNumericType;
+import org.opensearch.search.aggregations.metrics.CompensatedSum;
+
+/**
+ * Sum value aggregator for star tree
+ *
+ * @opensearch.experimental
+ */
+public class SumValueAggregator implements ValueAggregator<Double> {
+
+    public static final StarTreeNumericType VALUE_AGGREGATOR_TYPE = StarTreeNumericType.DOUBLE;
+    private double sum = 0;
+    private double compensation = 0;
+    private CompensatedSum kahanSummation = new CompensatedSum(0, 0);
+
+    @Override
+    public MetricStat getAggregationType() {
+        return MetricStat.SUM;
+    }
+
+    @Override
+    public StarTreeNumericType getAggregatedValueType() {
+        return VALUE_AGGREGATOR_TYPE;
+    }
+
+    @Override
+    public Double getInitialAggregatedValueForSegmentDocValue(Long segmentDocValue, StarTreeNumericType starTreeNumericType) {
+        kahanSummation.reset(0, 0);
+        kahanSummation.add(starTreeNumericType.getDoubleValue(segmentDocValue));
+        compensation = kahanSummation.delta();
+        sum = kahanSummation.value();
+        return kahanSummation.value();
+    }
+
+    @Override
+    public Double mergeAggregatedValueAndSegmentValue(Double value, Long segmentDocValue, StarTreeNumericType starTreeNumericType) {
+        assert kahanSummation.value() == value;
+        kahanSummation.reset(sum, compensation);
+        kahanSummation.add(starTreeNumericType.getDoubleValue(segmentDocValue));
+        compensation = kahanSummation.delta();
+        sum = kahanSummation.value();
+        return kahanSummation.value();
+    }
+
+    @Override
+    public Double mergeAggregatedValues(Double value, Double aggregatedValue) {
+        assert kahanSummation.value() == aggregatedValue;
+        kahanSummation.reset(sum, compensation);
+        kahanSummation.add(value);
+        compensation = kahanSummation.delta();
+        sum = kahanSummation.value();
+        return kahanSummation.value();
+    }
+
+    @Override
+    public Double getInitialAggregatedValue(Double value) {
+        kahanSummation.reset(0, 0);
+        kahanSummation.add(value);
+        compensation = kahanSummation.delta();
+        sum = kahanSummation.value();
+        return kahanSummation.value();
+    }
+
+    @Override
+    public int getMaxAggregatedValueByteSize() {
+        return Double.BYTES;
+    }
+
+    @Override
+    public Long toLongValue(Double value) {
+        try {
+            return NumericUtils.doubleToSortableLong(value);
+        } catch (Exception e) {
+            throw new IllegalStateException("Cannot convert " + value + " to sortable long", e);
+        }
+    }
+
+    @Override
+    public Double toStarTreeNumericTypeValue(Long value, StarTreeNumericType type) {
+        try {
+            return type.getDoubleValue(value);
+        } catch (Exception e) {
+            throw new IllegalStateException("Cannot convert " + value + " to sortable aggregation type", e);
+        }
+    }
+}