SOLR-11595: optimize SolrIndexSearcher.collectionStatistics

solr/CHANGES.txt

@@ -123,6 +123,9 @@ Optimizations
 * SOLR-11641: Change `frange` to default to `cost=100` so default behavior is to PostFilter if user specifies
   `cache=false` (hossman)
 
+* SOLR-11595: SolrIndexSearcher.localCollectionStatistics is now faster by leveraging an existing
+  cached MultiFields.  Noticeable when many fields are searched.  (David Smiley)
+
 Other Changes
 ----------------------
 * SOLR-11478: Solr should remove itself from live_nodes in zk immediately on shutdown. (Cao Manh Dat)

solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java

@@ -367,7 +367,15 @@ public class SolrIndexSearcher extends IndexSearcher implements Closeable, SolrI
   }
 
   public CollectionStatistics localCollectionStatistics(String field) throws IOException {
-    return super.collectionStatistics(field);
+    // Could call super.collectionStatistics(field); but we can use a cached MultiTerms
+    assert field != null;
+    // SlowAtomicReader has a cache of MultiTerms
+    Terms terms = getSlowAtomicReader().terms(field);
+    if (terms == null) {
+      return null;
+    }
+    return new CollectionStatistics(field, reader.maxDoc(),
+        terms.getDocCount(), terms.getSumTotalTermFreq(), terms.getSumDocFreq());
   }
 
   public boolean isCachingEnabled() {