Copy metrics and default_metric properties when downsampling aggregate_metric_double

Author: jordan-powers

modules/data-streams/src/main/java/org/elasticsearch/datastreams/DataStreamFeatures.java

@@ -21,13 +21,17 @@ public class DataStreamFeatures implements FeatureSpecification {
 
     public static final NodeFeature DATA_STREAM_FAILURE_STORE_TSDB_FIX = new NodeFeature("data_stream.failure_store.tsdb_fix");
 
+    public static final NodeFeature DOWNSAMPLE_AGGREGATE_DEFAULT_METRIC_FIX = new NodeFeature(
+        "data_stream.downsample.default_aggregate_metric_fix"
+    );
+
     @Override
     public Set<NodeFeature> getFeatures() {
         return Set.of();
     }
 
     @Override
     public Set<NodeFeature> getTestFeatures() {
-        return Set.of(DATA_STREAM_FAILURE_STORE_TSDB_FIX);
+        return Set.of(DATA_STREAM_FAILURE_STORE_TSDB_FIX, DOWNSAMPLE_AGGREGATE_DEFAULT_METRIC_FIX);
     }
 }

x-pack/plugin/downsample/qa/rest/src/yamlRestTest/resources/rest-api-spec/test/downsample/80_re_downsample.yml renamed to x-pack/plugin/downsample/qa/rest/src/yamlRestTest/resources/rest-api-spec/test/downsample/80_downsample_aggregate.yml

@@ -1,7 +1,7 @@
-"Downsample index":
+"downsample aggregate field":
   - requires:
-      cluster_features: ["gte_v8.13.0"]
-      reason: _tsid hashing introduced in 8.13
+      cluster_features: ["data_stream.downsample.default_aggregate_metric_fix"]
+      reason: "#119696 fixed"
 
   - do:
       indices.create:

x-pack/plugin/downsample/src/main/java/org/elasticsearch/xpack/downsample/TransportDownsampleAction.java

@@ -91,6 +91,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -752,9 +753,22 @@ private static void addMetricFieldMapping(final XContentBuilder builder, final S
                 builder.field(fieldProperty, fieldProperties.get(fieldProperty));
             }
         } else {
-            final String[] supportedAggsArray = metricType.supportedAggs();
+            List<String> supportedAggs = List.of(metricType.supportedAggs());
             // We choose max as the default metric
-            final String defaultMetric = List.of(supportedAggsArray).contains("max") ? "max" : supportedAggsArray[0];
+            String defaultMetric = supportedAggs.contains("max") ? "max" : supportedAggs.get(0);
+
+            if (fieldProperties.get("type").equals(AggregateMetricDoubleFieldMapper.CONTENT_TYPE)) {
+                @SuppressWarnings("unchecked")
+                List<String> currentAggs = (List<String>) fieldProperties.get(AggregateMetricDoubleFieldMapper.Names.METRICS);
+                supportedAggs = supportedAggs.stream().filter(currentAggs::contains).toList();
+                defaultMetric = Objects.requireNonNullElse(
+                    (String) fieldProperties.get(AggregateMetricDoubleFieldMapper.Names.DEFAULT_METRIC),
+                    defaultMetric
+                );
+            }
+
+            String[] supportedAggsArray = supportedAggs.toArray(String[]::new);
+
             builder.field("type", AggregateMetricDoubleFieldMapper.CONTENT_TYPE)
                 .array(AggregateMetricDoubleFieldMapper.Names.METRICS, supportedAggsArray)
                 .field(AggregateMetricDoubleFieldMapper.Names.DEFAULT_METRIC, defaultMetric)