Add cluster setting for TDigestExecutionHint

docs/changelog/96914.yaml

@@ -0,0 +1,5 @@
+pr: 96914
+summary: Add cluster setting for TDigestExecutionHint
+area: Aggregations
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java

@@ -110,6 +110,7 @@
 import org.elasticsearch.search.SearchModule;
 import org.elasticsearch.search.SearchService;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService;
+import org.elasticsearch.search.aggregations.metrics.TDigestExecutionHint;
 import org.elasticsearch.search.fetch.subphase.highlight.FastVectorHighlighter;
 import org.elasticsearch.snapshots.InternalSnapshotsInfoService;
 import org.elasticsearch.snapshots.RestoreService;
@@ -576,7 +577,8 @@ public void apply(Settings value, Settings current, Settings previous) {
         IndicesClusterStateService.SHARD_LOCK_RETRY_INTERVAL_SETTING,
         IndicesClusterStateService.SHARD_LOCK_RETRY_TIMEOUT_SETTING,
         IngestSettings.GROK_WATCHDOG_INTERVAL,
-        IngestSettings.GROK_WATCHDOG_MAX_EXECUTION_TIME
+        IngestSettings.GROK_WATCHDOG_MAX_EXECUTION_TIME,
+        TDigestExecutionHint.SETTING
     ).filter(Objects::nonNull).collect(Collectors.toSet());
 
     static List<SettingUpgrader<?>> BUILT_IN_SETTING_UPGRADERS = Collections.emptyList();

server/src/main/java/org/elasticsearch/search/SearchService.java

@@ -74,6 +74,7 @@
 import org.elasticsearch.search.aggregations.AggregatorFactories;
 import org.elasticsearch.search.aggregations.MultiBucketConsumerService;
 import org.elasticsearch.search.aggregations.SearchContextAggregations;
+import org.elasticsearch.search.aggregations.metrics.TDigestExecutionHint;
 import org.elasticsearch.search.aggregations.support.AggregationContext;
 import org.elasticsearch.search.aggregations.support.AggregationContext.ProductionAggregationContext;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
@@ -329,6 +330,9 @@ public SearchService(
         enableRewriteAggsToFilterByFilter = ENABLE_REWRITE_AGGS_TO_FILTER_BY_FILTER.get(settings);
         clusterService.getClusterSettings()
             .addSettingsUpdateConsumer(ENABLE_REWRITE_AGGS_TO_FILTER_BY_FILTER, this::setEnableRewriteAggsToFilterByFilter);
+
+        TDigestExecutionHint.SETTING.get(settings);
+        clusterService.getClusterSettings().addSettingsUpdateConsumer(TDigestExecutionHint.SETTING, TDigestExecutionHint::setDefaultValue);
     }
 
     private static void validateKeepAlives(TimeValue defaultKeepAlive, TimeValue maxKeepAlive) {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/TDigestExecutionHint.java

@@ -11,6 +11,7 @@
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
+import org.elasticsearch.common.settings.Setting;
 
 import java.io.IOException;
 
@@ -21,6 +22,24 @@ public enum TDigestExecutionHint implements Writeable {
     DEFAULT(0),        // Use a TDigest that is optimized for performance, with a small penalty in accuracy.
     HIGH_ACCURACY(1);  // Use a TDigest that is optimize for accuracy, at the expense of performance.
 
+    public static final Setting<String> SETTING = Setting.simpleString(
+        "search.aggs.tdigest_execution_hint",
+        "",
+        TDigestExecutionHint::parse,
+        Setting.Property.NodeScope,
+        Setting.Property.Dynamic
+    );
+
+    private static volatile TDigestExecutionHint defaultHint = DEFAULT;
+
+    public static TDigestExecutionHint getDefaultValue() {
+        return defaultHint;
+    }
+
+    public static void setDefaultValue(String value) {
+        defaultHint = parse(value);
+    }
+
     TDigestExecutionHint(int id) {
         this.id = id;
     }

server/src/main/java/org/elasticsearch/search/aggregations/metrics/TDigestState.java

@@ -76,6 +76,10 @@ public static TDigestState createOptimizedForAccuracy(double compression) {
      * @return a TDigestState object
      */
     public static TDigestState create(double compression, TDigestExecutionHint executionHint) {
+        if (executionHint == TDigestExecutionHint.DEFAULT) {
+            // Check for overrides through cluster settings.
+            executionHint = TDigestExecutionHint.getDefaultValue();
+        }
         return switch (executionHint) {
             case HIGH_ACCURACY -> createOptimizedForAccuracy(compression);
             case DEFAULT -> create(compression);

server/src/test/java/org/elasticsearch/search/aggregations/metrics/TDigestExecutionHintTests.java

@@ -32,6 +32,17 @@ public void testParsing() {
         expectThrows(IllegalArgumentException.class, () -> TDigestExecutionHint.parse("NO SUCH HINT"));
     }
 
+    public void testDefaultValue() {
+        assertEquals(TDigestExecutionHint.DEFAULT, TDigestExecutionHint.getDefaultValue());
+
+        TDigestExecutionHint.setDefaultValue(TDigestExecutionHint.HIGH_ACCURACY.toString());
+        assertEquals(TDigestExecutionHint.HIGH_ACCURACY, TDigestExecutionHint.getDefaultValue());
+
+        TDigestExecutionHint hint = randomFrom(TDigestExecutionHint.values());
+        TDigestExecutionHint.setDefaultValue(hint.toString());
+        assertEquals(hint, TDigestExecutionHint.getDefaultValue());
+    }
+
     private static TDigestExecutionHint writeToAndReadFrom(TDigestExecutionHint state) throws IOException {
         try (BytesStreamOutput out = new BytesStreamOutput()) {
             state.writeTo(out);

server/src/test/java/org/elasticsearch/search/aggregations/metrics/TDigestStateTests.java

@@ -162,6 +162,29 @@ public void testFactoryMethods() {
         assertNotEquals(anotherFast, anotherAccurate);
     }
 
+    public void testOverrideDefaultType() {
+        TDigestState fast = TDigestState.create(100);
+        TDigestState accurate = TDigestState.createOptimizedForAccuracy(100);
+
+        TDigestExecutionHint.setDefaultValue(TDigestExecutionHint.HIGH_ACCURACY.toString());
+        TDigestState anotherAccurate = TDigestState.create(100, TDigestExecutionHint.DEFAULT);
+
+        TDigestExecutionHint.setDefaultValue(TDigestExecutionHint.DEFAULT.toString());
+        TDigestState anotherFast = TDigestState.create(100, TDigestExecutionHint.DEFAULT);
+
+        for (int i = 0; i < 100; i++) {
+            fast.add(i);
+            anotherFast.add(i);
+            accurate.add(i);
+            anotherAccurate.add(i);
+        }
+
+        assertEquals(fast, anotherFast);
+        assertEquals(accurate, anotherAccurate);
+        assertNotEquals(fast, accurate);
+        assertNotEquals(anotherFast, anotherAccurate);
+    }
+
     private static TDigestState writeToAndReadFrom(TDigestState state, TransportVersion version) throws IOException {
         BytesRef serializedAggs = serialize(state, version);
         try (