db_bench: introduce --benchmark_read_rate_limit

Summary:
Add the parameter in db_bench to help users to measure latency histogram with constant read rate.
Closes https://github.com/facebook/rocksdb/pull/1683

Differential Revision: D4341387

Pulled By: siying

fbshipit-source-id: 1b4b276

tools/db_bench_tool.cc

@@ -752,6 +752,11 @@ DEFINE_uint64(
     "If non-zero, db_bench will rate-limit the writes going into RocksDB. This "
     "is the global rate in bytes/second.");
 
+DEFINE_uint64(
+    benchmark_read_rate_limit, 0,
+    "If non-zero, db_bench will rate-limit the reads from RocksDB. This "
+    "is the global rate in ops/second.");
+
 DEFINE_uint64(max_compaction_bytes, rocksdb::Options().max_compaction_bytes,
               "Max bytes allowed in one compaction");
 
@@ -1667,6 +1672,7 @@ struct SharedState {
   int total;
   int perf_level;
   std::shared_ptr<RateLimiter> write_rate_limiter;
+  std::shared_ptr<RateLimiter> read_rate_limiter;
 
   // Each thread goes through the following states:
   //    (1) initializing
@@ -1821,6 +1827,8 @@ class Benchmark {
              / 1048576.0));
     fprintf(stdout, "Write rate: %" PRIu64 " bytes/second\n",
             FLAGS_benchmark_write_rate_limit);
+    fprintf(stdout, "Read rate: %" PRIu64 " ops/second\n",
+            FLAGS_benchmark_read_rate_limit);
     if (FLAGS_enable_numa) {
       fprintf(stderr, "Running in NUMA enabled mode.\n");
 #ifndef NUMA
@@ -2478,6 +2486,10 @@ class Benchmark {
       shared.write_rate_limiter.reset(
           NewGenericRateLimiter(FLAGS_benchmark_write_rate_limit));
     }
+    if (FLAGS_benchmark_read_rate_limit > 0) {
+      shared.read_rate_limiter.reset(
+          NewGenericRateLimiter(FLAGS_benchmark_read_rate_limit));
+    }
 
     std::unique_ptr<ReporterAgent> reporter_agent;
     if (FLAGS_report_interval_seconds > 0) {
@@ -3629,7 +3641,13 @@ class Benchmark {
       bytes += iter->key().size() + iter->value().size();
       thread->stats.FinishedOps(nullptr, db, 1, kRead);
       ++i;
+
+      if (thread->shared->read_rate_limiter.get() != nullptr &&
+          i % 1024 == 1023) {
+        thread->shared->read_rate_limiter->Request(1024, Env::IO_HIGH);
+      }
     }
+
     delete iter;
     thread->stats.AddBytes(bytes);
     if (FLAGS_perf_level > rocksdb::PerfLevel::kDisable) {
@@ -3655,6 +3673,10 @@ class Benchmark {
       bytes += iter->key().size() + iter->value().size();
       thread->stats.FinishedOps(nullptr, db, 1, kRead);
       ++i;
+      if (thread->shared->read_rate_limiter.get() != nullptr &&
+          i % 1024 == 1023) {
+        thread->shared->read_rate_limiter->Request(1024, Env::IO_HIGH);
+      }
     }
     delete iter;
     thread->stats.AddBytes(bytes);
@@ -3693,6 +3715,10 @@ class Benchmark {
           ++nonexist;
         }
       }
+      if (thread->shared->read_rate_limiter.get() != nullptr) {
+        thread->shared->read_rate_limiter->Request(100, Env::IO_HIGH);
+      }
+
       thread->stats.FinishedOps(nullptr, db, 100, kRead);
     } while (!duration.Done(100));
 
@@ -3761,6 +3787,12 @@ class Benchmark {
         fprintf(stderr, "Get returned an error: %s\n", s.ToString().c_str());
         abort();
       }
+
+      if (thread->shared->read_rate_limiter.get() != nullptr &&
+          read % 256 == 255) {
+        thread->shared->read_rate_limiter->Request(256, Env::IO_HIGH);
+      }
+
       thread->stats.FinishedOps(db_with_cfh, db_with_cfh->db, 1, kRead);
     }
 
@@ -3780,6 +3812,7 @@ class Benchmark {
   // Returns the total number of keys found.
   void MultiReadRandom(ThreadState* thread) {
     int64_t read = 0;
+    int64_t num_multireads = 0;
     int64_t found = 0;
     ReadOptions options(FLAGS_verify_checksum, true);
     std::vector<Slice> keys;
@@ -3800,6 +3833,7 @@ class Benchmark {
       assert(static_cast<int64_t>(statuses.size()) == entries_per_batch_);
 
       read += entries_per_batch_;
+      num_multireads++;
       for (int64_t i = 0; i < entries_per_batch_; ++i) {
         if (statuses[i].ok()) {
           ++found;
@@ -3809,6 +3843,11 @@ class Benchmark {
           abort();
         }
       }
+      if (thread->shared->read_rate_limiter.get() != nullptr &&
+          num_multireads % 256 == 255) {
+        thread->shared->read_rate_limiter->Request(256 * entries_per_batch_,
+                                                   Env::IO_HIGH);
+      }
       thread->stats.FinishedOps(nullptr, db, entries_per_batch_, kRead);
     }
 
@@ -3902,6 +3941,11 @@ class Benchmark {
         assert(iter_to_use->status().ok());
       }
 
+      if (thread->shared->read_rate_limiter.get() != nullptr &&
+          read % 256 == 255) {
+        thread->shared->read_rate_limiter->Request(256, Env::IO_HIGH);
+      }
+
       thread->stats.FinishedOps(&db_, db_.db, 1, kSeek);
     }
     delete single_iter;
@@ -4699,6 +4743,10 @@ class Benchmark {
         }
       }
       found += key_found;
+
+      if (thread->shared->read_rate_limiter.get() != nullptr) {
+        thread->shared->read_rate_limiter->Request(1, Env::IO_HIGH);
+      }
     }
     delete iter;