ES|QL block type for exponential histograms

libs/exponential-histogram/src/main/java/module-info.java

@@ -0,0 +1,26 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+module org.elasticsearch.exponentialhistogram {
+    requires org.elasticsearch.xcontent;
+    requires org.apache.lucene.core;
+    requires org.elasticsearch.base;
+
+    exports org.elasticsearch.exponentialhistogram;
+}

x-pack/plugin/esql-core/src/main/java/org/elasticsearch/xpack/esql/core/plugin/EsqlCorePlugin.java

@@ -15,4 +15,5 @@ public class EsqlCorePlugin extends Plugin implements ExtensiblePlugin {
 
     public static final FeatureFlag AGGREGATE_METRIC_DOUBLE_FEATURE_FLAG = new FeatureFlag("esql_aggregate_metric_double");
     public static final FeatureFlag DENSE_VECTOR_FEATURE_FLAG = new FeatureFlag("esql_dense_vector");
+    public static final FeatureFlag EXPONENTIAL_HISTOGRAM_FEATURE_FLAG = new FeatureFlag("esql_exponential_histogram");
 }

x-pack/plugin/esql-core/src/main/java/org/elasticsearch/xpack/esql/core/type/DataType.java

@@ -307,6 +307,8 @@ public enum DataType {
 
     AGGREGATE_METRIC_DOUBLE(builder().esType("aggregate_metric_double").estimatedSize(Double.BYTES * 3 + Integer.BYTES)),
 
+    EXPONENTIAL_HISTOGRAM(builder().esType("exponential_histogram").unknownSize().docValues()),
+
     /**
      * Fields with this type are dense vectors, represented as an array of double values.
      */
@@ -320,7 +322,8 @@ public enum DataType {
      */
     public static final Map<DataType, FeatureFlag> UNDER_CONSTRUCTION = Map.ofEntries(
         Map.entry(AGGREGATE_METRIC_DOUBLE, EsqlCorePlugin.AGGREGATE_METRIC_DOUBLE_FEATURE_FLAG),
-        Map.entry(DENSE_VECTOR, EsqlCorePlugin.DENSE_VECTOR_FEATURE_FLAG)
+        Map.entry(DENSE_VECTOR, EsqlCorePlugin.DENSE_VECTOR_FEATURE_FLAG),
+        Map.entry(EXPONENTIAL_HISTOGRAM, EsqlCorePlugin.EXPONENTIAL_HISTOGRAM_FEATURE_FLAG)
     );
 
     private final String typeName;

x-pack/plugin/esql/build.gradle

@@ -42,6 +42,7 @@ dependencies {
   implementation project('compute:ann')
   implementation project(':libs:dissect')
   implementation project(':libs:grok')
+  implementation project(':libs:exponential-histogram')
   api "org.apache.lucene:lucene-spatial3d:${versions.lucene}"
   api project(":libs:h3")
   implementation project('arrow')

x-pack/plugin/esql/compute/build.gradle

@@ -16,6 +16,7 @@ dependencies {
   compileOnly project(xpackModule('ml'))
   annotationProcessor project('gen')
   implementation 'com.carrotsearch:hppc:0.8.1'
+  api project(':libs:exponential-histogram')
 
   testImplementation(project(':modules:analysis-common'))
   testImplementation(project(':test:framework'))

x-pack/plugin/esql/compute/src/main/java/module-info.java

@@ -21,6 +21,7 @@
     requires org.elasticsearch.geo;
     requires org.elasticsearch.xcore;
     requires hppc;
+    requires org.elasticsearch.exponentialhistogram;
 
     exports org.elasticsearch.compute;
     exports org.elasticsearch.compute.aggregation;

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/BlockFactory.java

@@ -14,6 +14,7 @@
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.common.util.BytesRefArray;
 import org.elasticsearch.compute.data.Block.MvOrdering;
+import org.elasticsearch.exponentialhistogram.ExponentialHistogram;
 
 import java.util.BitSet;
 
@@ -467,6 +468,19 @@ public final AggregateMetricDoubleBlock newConstantAggregateMetricDoubleBlock(
         }
     }
 
+    public ExponentialHistogramBlockBuilder newExponentialHistogramBlockBuilder(int estimatedSize) {
+        return new ExponentialHistogramBlockBuilder(estimatedSize, this);
+    }
+
+    public final ExponentialHistogramBlock newConstantExponentialHistogramBlock(ExponentialHistogram value, int positionCount) {
+        try (ExponentialHistogramBlockBuilder builder = newExponentialHistogramBlockBuilder(positionCount)) {
+            for (int i = 0; i < positionCount; i++) {
+                builder.append(value);
+            }
+            return builder.build();
+        }
+    }
+
     public final AggregateMetricDoubleBlock newAggregateMetricDoubleBlock(
         double[] minValues,
         double[] maxValues,

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/BlockUtils.java

@@ -12,6 +12,8 @@
 import org.elasticsearch.compute.data.AggregateMetricDoubleBlockBuilder.AggregateMetricDoubleLiteral;
 import org.elasticsearch.core.Releasable;
 import org.elasticsearch.core.Releasables;
+import org.elasticsearch.exponentialhistogram.ExponentialHistogram;
+import org.elasticsearch.exponentialhistogram.ExponentialHistogramCircuitBreaker;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -217,6 +219,7 @@ public static void appendValue(Block.Builder builder, Object val, ElementType ty
             case FLOAT -> ((FloatBlock.Builder) builder).appendFloat((Float) val);
             case DOUBLE -> ((DoubleBlock.Builder) builder).appendDouble((Double) val);
             case BOOLEAN -> ((BooleanBlock.Builder) builder).appendBoolean((Boolean) val);
+            case EXPONENTIAL_HISTOGRAM -> ((ExponentialHistogramBlockBuilder) builder).append((ExponentialHistogram) val);
             default -> throw new UnsupportedOperationException("unsupported element type [" + type + "]");
         }
     }
@@ -246,6 +249,7 @@ private static Block constantBlock(BlockFactory blockFactory, ElementType type,
             case BOOLEAN -> blockFactory.newConstantBooleanBlockWith((boolean) val, size);
             case AGGREGATE_METRIC_DOUBLE -> blockFactory.newConstantAggregateMetricDoubleBlock((AggregateMetricDoubleLiteral) val, size);
             case FLOAT -> blockFactory.newConstantFloatBlockWith((float) val, size);
+            case EXPONENTIAL_HISTOGRAM -> blockFactory.newConstantExponentialHistogramBlock((ExponentialHistogram) val, size);
             default -> throw new UnsupportedOperationException("unsupported element type [" + type + "]");
         };
     }
@@ -299,6 +303,11 @@ yield new AggregateMetricDoubleLiteral(
                     aggBlock.countBlock().getInt(offset)
                 );
             }
+            case EXPONENTIAL_HISTOGRAM -> {
+                ExponentialHistogram histogram = ((ExponentialHistogramArrayBlock) block).getExponentialHistogram(offset);
+                // return a copy so that the returned value is not bound to the lifetime of the block
+                yield ExponentialHistogram.builder(histogram, ExponentialHistogramCircuitBreaker.noop()).build();
+            }
             case UNKNOWN -> throw new IllegalArgumentException("can't read values from [" + block + "]");
         };
     }

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/ConstantNullBlock.java

@@ -12,6 +12,7 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.core.ReleasableIterator;
+import org.elasticsearch.exponentialhistogram.ExponentialHistogram;
 
 import java.io.IOException;
 
@@ -26,7 +27,8 @@ public final class ConstantNullBlock extends AbstractNonThreadSafeRefCounted
         FloatBlock,
         DoubleBlock,
         BytesRefBlock,
-        AggregateMetricDoubleBlock {
+        AggregateMetricDoubleBlock,
+        ExponentialHistogramBlock {
 
     private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(ConstantNullBlock.class);
     private final int positionCount;
@@ -292,6 +294,12 @@ public long getLong(int valueIndex) {
         throw new UnsupportedOperationException("null block");
     }
 
+    @Override
+    public ExponentialHistogram getExponentialHistogram(int valueIndex) {
+        assert false : "null block";
+        throw new UnsupportedOperationException("null block");
+    }
+
     @Override
     public int getTotalValueCount() {
         return 0;

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/data/ElementType.java

@@ -11,6 +11,7 @@
 import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.exponentialhistogram.ExponentialHistogram;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -64,6 +65,16 @@ public enum ElementType {
         "AggregateMetricDouble",
         BlockFactory::newAggregateMetricDoubleBlockBuilder,
         AggregateMetricDoubleArrayBlock::readFrom
+    ),
+
+    /**
+     * Blocks that contain exponential_histograms.
+     */
+    EXPONENTIAL_HISTOGRAM(
+        11,
+        "ExponentialHistogram",
+        BlockFactory::newExponentialHistogramBlockBuilder,
+        ExponentialHistogramArrayBlock::readFrom
     );
 
     private interface BuilderSupplier {
@@ -111,6 +122,8 @@ public static ElementType fromJava(Class<?> type) {
             elementType = BOOLEAN;
         } else if (type == AggregateMetricDoubleBlockBuilder.AggregateMetricDoubleLiteral.class) {
             elementType = AGGREGATE_METRIC_DOUBLE;
+        } else if (type != null && ExponentialHistogram.class.isAssignableFrom(type)) {
+            elementType = EXPONENTIAL_HISTOGRAM;
         } else if (type == null || type == Void.class) {
             elementType = NULL;
         } else {