add ff creation benchmark

src/fastfield/multivalued/mod.rs

@@ -428,7 +428,7 @@ mod bench {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
             let mut serializer = CompositeFastFieldSerializer::from_write(write).unwrap();
             let mut fast_field_writers = FastFieldsWriter::from_schema(&schema);
-            for block in &multi_values(num_docs, 1) {
+            for block in &multi_values(num_docs, 3) {
                 let mut doc = Document::new();
                 for val in block {
                     doc.add_u64(field, *val);
@@ -469,4 +469,34 @@ mod bench {
             });
         }
     }
+
+    #[bench]
+    fn bench_multi_value_ff_creation(b: &mut Bencher) {
+        // 3 million ff entries
+        let num_docs = 1_000_000;
+        let multi_values = multi_values(num_docs, 3);
+
+        b.iter(|| {
+            let directory: RamDirectory = RamDirectory::create();
+            let options = NumericOptions::default().set_fast(Cardinality::MultiValues);
+            let mut schema_builder = Schema::builder();
+            let field = schema_builder.add_u64_field("field", options);
+            let schema = schema_builder.build();
+
+            let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
+            let mut serializer = CompositeFastFieldSerializer::from_write(write).unwrap();
+            let mut fast_field_writers = FastFieldsWriter::from_schema(&schema);
+            for block in &multi_values {
+                let mut doc = Document::new();
+                for val in block {
+                    doc.add_u64(field, *val);
+                }
+                fast_field_writers.add_document(&doc);
+            }
+            fast_field_writers
+                .serialize(&mut serializer, &HashMap::new(), None)
+                .unwrap();
+            serializer.close().unwrap();
+        });
+    }
 }