Add max_background_jobs to db_bench

Summary:
As titled. Also fixed an off-by-one error causing us to add one less range deletion than the user specified.
Closes https://github.com/facebook/rocksdb/pull/2544

Differential Revision: D5383451

Pulled By: ajkr

fbshipit-source-id: cbd5890c33f09bbb5c0c1f4bb952a1add32336e0

tools/db_bench_tool.cc

@@ -313,6 +313,11 @@ DEFINE_int32(max_write_buffer_number_to_maintain,
              "after they are flushed.  If this value is set to -1, "
              "'max_write_buffer_number' will be used.");
 
+DEFINE_int32(max_background_jobs,
+             rocksdb::Options().max_background_jobs,
+             "The maximum number of concurrent background jobs that can occur "
+             "in parallel.");
+
 DEFINE_int32(max_background_compactions,
              rocksdb::Options().max_background_compactions,
              "The maximum number of concurrent background compactions"
@@ -2855,6 +2860,7 @@ void VerifyDBFromDB(std::string& truth_db_name) {
       FLAGS_min_write_buffer_number_to_merge;
     options.max_write_buffer_number_to_maintain =
         FLAGS_max_write_buffer_number_to_maintain;
+    options.max_background_jobs = FLAGS_max_background_jobs;
     options.max_background_compactions = FLAGS_max_background_compactions;
     options.max_subcompactions = static_cast<uint32_t>(FLAGS_subcompactions);
     options.max_background_flushes = FLAGS_max_background_flushes;
@@ -3494,7 +3500,7 @@ void VerifyDBFromDB(std::string& truth_db_name) {
         bytes += value_size_ + key_size_;
         ++num_written;
         if (writes_per_range_tombstone_ > 0 &&
-            num_written / writes_per_range_tombstone_ <
+            num_written / writes_per_range_tombstone_ <=
                 max_num_range_tombstones_ &&
             num_written % writes_per_range_tombstone_ == 0) {
           int64_t begin_num = key_gens[id]->Next();