Add multireadwhilewriting benchmark to db_bench (#10919)

Summary:
Add the new benchmark

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10919

Reviewed By: akankshamahajan15

Differential Revision: D41017025

Pulled By: anand1976

fbshipit-source-id: 5220815d66de1f689b7f09d9c5266cebf4e345d1

tools/db_bench_tool.cc

@@ -3498,6 +3498,11 @@ class Benchmark {
         fprintf(stderr, "entries_per_batch = %" PRIi64 "\n",
                 entries_per_batch_);
         method = &Benchmark::MultiReadRandom;
+      } else if (name == "multireadwhilewriting") {
+        fprintf(stderr, "entries_per_batch = %" PRIi64 "\n",
+                entries_per_batch_);
+        num_threads++;
+        method = &Benchmark::MultiReadWhileWriting;
       } else if (name == "approximatesizerandom") {
         fprintf(stderr, "entries_per_batch = %" PRIi64 "\n",
                 entries_per_batch_);
@@ -6895,6 +6900,14 @@ class Benchmark {
     }
   }
 
+  void MultiReadWhileWriting(ThreadState* thread) {
+    if (thread->tid > 0) {
+      MultiReadRandom(thread);
+    } else {
+      BGWriter(thread, kWrite);
+    }
+  }
+
   void ReadWhileMerging(ThreadState* thread) {
     if (thread->tid > 0) {
       ReadRandom(thread);