Fixed the db_bench MergeRandom only access CF_default (#4155)

Summary:
When running the tracing and analyzing, I found that MergeRandom benchmark in db_bench only access the default column family even the -num_column_families is specified > 1.

changes: Using the db_with_cfh as DB to randomly select the column family to execute the Merge operation if -num_column_families is specified > 1.

Tested with make asan_check and verified in tracing
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4155

Differential Revision: D8907888

Pulled By: zhichao-cao

fbshipit-source-id: 2b4bc8fe0e99c8f262f5be6b986c7025d62cf850

tools/db_bench_tool.cc

@@ -5061,17 +5061,27 @@ void VerifyDBFromDB(std::string& truth_db_name) {
     // The number of iterations is the larger of read_ or write_
     Duration duration(FLAGS_duration, readwrites_);
     while (!duration.Done(1)) {
-      DB* db = SelectDB(thread);
-      GenerateKeyFromInt(thread->rand.Next() % merge_keys_, merge_keys_, &key);
+      DBWithColumnFamilies* db_with_cfh = SelectDBWithCfh(thread);
+      int64_t key_rand = thread->rand.Next() % merge_keys_;
+      GenerateKeyFromInt(key_rand, merge_keys_, &key);
 
-      Status s = db->Merge(write_options_, key, gen.Generate(value_size_));
+      Status s;
+      if (FLAGS_num_column_families > 1) {
+        s = db_with_cfh->db->Merge(write_options_,
+                                   db_with_cfh->GetCfh(key_rand), key,
+                                   gen.Generate(value_size_));
+      } else {
+        s = db_with_cfh->db->Merge(write_options_,
+                                   db_with_cfh->db->DefaultColumnFamily(), key,
+                                   gen.Generate(value_size_));
+      }
 
       if (!s.ok()) {
         fprintf(stderr, "merge error: %s\n", s.ToString().c_str());
         exit(1);
       }
       bytes += key.size() + value_size_;
-      thread->stats.FinishedOps(nullptr, db, 1, kMerge);
+      thread->stats.FinishedOps(nullptr, db_with_cfh->db, 1, kMerge);
     }
 
     // Print some statistics