Fix needsScore computation in GlobalOrdCardinalityAggregator (elastic#113129)

Only use TOP_DOCS if we are going to use dynamic pruning.

Author: iverase

docs/changelog/113129.yaml

@@ -0,0 +1,6 @@
+pr: 113129
+summary: Fix `needsScore` computation in `GlobalOrdCardinalityAggregator`
+area: Aggregations
+type: bug
+issues:
+ - 112975

server/src/internalClusterTest/java/org/elasticsearch/search/aggregations/bucket/NestedIT.java

@@ -8,6 +8,7 @@
 package org.elasticsearch.search.aggregations.bucket;
 
 import org.apache.lucene.search.join.ScoreMode;
+import org.elasticsearch.action.admin.indices.delete.DeleteIndexRequest;
 import org.elasticsearch.action.index.IndexRequestBuilder;
 import org.elasticsearch.action.search.SearchRequestBuilder;
 import org.elasticsearch.index.query.InnerHitBuilder;
@@ -17,11 +18,15 @@
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.bucket.filter.Filter;
 import org.elasticsearch.search.aggregations.bucket.histogram.Histogram;
+import org.elasticsearch.search.aggregations.bucket.nested.InternalNested;
 import org.elasticsearch.search.aggregations.bucket.nested.Nested;
+import org.elasticsearch.search.aggregations.bucket.nested.NestedAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.terms.LongTerms;
 import org.elasticsearch.search.aggregations.bucket.terms.StringTerms;
 import org.elasticsearch.search.aggregations.bucket.terms.Terms;
 import org.elasticsearch.search.aggregations.bucket.terms.Terms.Bucket;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.metrics.CardinalityAggregationBuilder;
 import org.elasticsearch.search.aggregations.metrics.Max;
 import org.elasticsearch.search.aggregations.metrics.Stats;
 import org.elasticsearch.search.aggregations.metrics.Sum;
@@ -889,4 +894,87 @@ public void testSyntheticSource() throws Exception {
             assertEquals("a", nested.get("number"));
         });
     }
+
+    public void testScoring() throws Exception {
+        assertAcked(
+            prepareCreate("scoring").setMapping(
+                jsonBuilder().startObject()
+                    .startObject("properties")
+                    .startObject("tags")
+                    .field("type", "nested")
+                    .startObject("properties")
+                    .startObject("key")
+                    .field("type", "keyword")
+                    .endObject()
+                    .startObject("value")
+                    .field("type", "keyword")
+                    .endObject()
+                    .endObject()
+                    .endObject()
+                    .endObject()
+                    .endObject()
+            )
+        );
+        ensureGreen("scoring");
+
+        prepareIndex("scoring").setId("1")
+            .setSource(
+                jsonBuilder().startObject()
+                    .startArray("tags")
+                    .startObject()
+                    .field("key", "state")
+                    .field("value", "texas")
+                    .endObject()
+                    .endArray()
+                    .endObject()
+            )
+            .get();
+        refresh("scoring");
+        prepareIndex("scoring").setId("2")
+            .setSource(
+                jsonBuilder().startObject()
+                    .startArray("tags")
+                    .startObject()
+                    .field("key", "state")
+                    .field("value", "utah")
+                    .endObject()
+                    .endArray()
+                    .endObject()
+            )
+            .get();
+        refresh("scoring");
+        prepareIndex("scoring").setId("3")
+            .setSource(
+                jsonBuilder().startObject()
+                    .startArray("tags")
+                    .startObject()
+                    .field("key", "state")
+                    .field("value", "texas")
+                    .endObject()
+                    .endArray()
+                    .endObject()
+            )
+            .get();
+        refresh("scoring");
+
+        assertResponse(
+            client().prepareSearch("scoring")
+                .setSize(0)
+                .addAggregation(
+                    new NestedAggregationBuilder("tags", "tags").subAggregation(
+                        new TermsAggregationBuilder("keys").field("tags.key")
+                            .executionHint("map")
+                            .subAggregation(new TermsAggregationBuilder("values").field("tags.value"))
+                            .subAggregation(new CardinalityAggregationBuilder("values_count").field("tags.value"))
+                    )
+                ),
+            searchResponse -> {
+                InternalNested nested = searchResponse.getAggregations().get("tags");
+                assertThat(nested.getDocCount(), equalTo(3L));
+                assertThat(nested.getAggregations().asList().size(), equalTo(1));
+            }
+        );
+
+        assertAcked(indicesAdmin().delete(new DeleteIndexRequest("scoring")).get());
+    }
 }

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

@@ -92,7 +92,12 @@ public GlobalOrdCardinalityAggregator(
 
     @Override
     public ScoreMode scoreMode() {
-        if (field != null && valuesSource.needsScores() == false && maxOrd <= MAX_FIELD_CARDINALITY_FOR_DYNAMIC_PRUNING) {
+        // this check needs to line up with the dynamic pruning as it is the
+        // only case where TOP_DOCS make sense.branch
+        if (this.parent == null
+            && field != null
+            && valuesSource.needsScores() == false
+            && maxOrd <= MAX_FIELD_CARDINALITY_FOR_DYNAMIC_PRUNING) {
             return ScoreMode.TOP_DOCS;
         } else if (valuesSource.needsScores()) {
             return ScoreMode.COMPLETE;