fix ThreadStatus for bottom-pri compaction threads

Summary:
added `ThreadType::BOTTOM_PRIORITY` which is used in the `ThreadStatus` object to indicate the thread is used for bottom-pri compactions. Previously there was a bug where we mislabeled such threads as `ThreadType::LOW_PRIORITY`.
Closes https://github.com/facebook/rocksdb/pull/3270

Differential Revision: D6559428

Pulled By: ajkr

fbshipit-source-id: 96b1a50a9c19492b1a5fd1b77cf7061a6f9f1d1c

db/db_test.cc

@@ -3488,12 +3488,16 @@ TEST_F(DBTest, GetThreadStatus) {
     const int kTestCount = 3;
     const unsigned int kHighPriCounts[kTestCount] = {3, 2, 5};
     const unsigned int kLowPriCounts[kTestCount] = {10, 15, 3};
+    const unsigned int kBottomPriCounts[kTestCount] = {2, 1, 4};
     for (int test = 0; test < kTestCount; ++test) {
       // Change the number of threads in high / low priority pool.
       env_->SetBackgroundThreads(kHighPriCounts[test], Env::HIGH);
       env_->SetBackgroundThreads(kLowPriCounts[test], Env::LOW);
+      env_->SetBackgroundThreads(kBottomPriCounts[test], Env::BOTTOM);
       // Wait to ensure the all threads has been registered
       unsigned int thread_type_counts[ThreadStatus::NUM_THREAD_TYPES];
+      // TODO(ajkr): it'd be better if SetBackgroundThreads returned only after
+      // all threads have been registered.
       // Try up to 60 seconds.
       for (int num_try = 0; num_try < 60000; num_try++) {
         env_->SleepForMicroseconds(1000);
@@ -3508,20 +3512,21 @@ TEST_F(DBTest, GetThreadStatus) {
         if (thread_type_counts[ThreadStatus::HIGH_PRIORITY] ==
                 kHighPriCounts[test] &&
             thread_type_counts[ThreadStatus::LOW_PRIORITY] ==
-                kLowPriCounts[test]) {
+                kLowPriCounts[test] &&
+            thread_type_counts[ThreadStatus::BOTTOM_PRIORITY] ==
+                kBottomPriCounts[test]) {
           break;
         }
       }
-      // Verify the total number of threades
-      ASSERT_EQ(thread_type_counts[ThreadStatus::HIGH_PRIORITY] +
-                    thread_type_counts[ThreadStatus::LOW_PRIORITY],
-                kHighPriCounts[test] + kLowPriCounts[test]);
       // Verify the number of high-priority threads
       ASSERT_EQ(thread_type_counts[ThreadStatus::HIGH_PRIORITY],
                 kHighPriCounts[test]);
       // Verify the number of low-priority threads
       ASSERT_EQ(thread_type_counts[ThreadStatus::LOW_PRIORITY],
                 kLowPriCounts[test]);
+      // Verify the number of bottom-priority threads
+      ASSERT_EQ(thread_type_counts[ThreadStatus::BOTTOM_PRIORITY],
+                kBottomPriCounts[test]);
     }
     if (i == 0) {
       // repeat the test with multiple column families

include/rocksdb/thread_status.h

@@ -45,6 +45,7 @@ struct ThreadStatus {
     HIGH_PRIORITY = 0,  // RocksDB BG thread in high-pri thread pool
     LOW_PRIORITY,  // RocksDB BG thread in low-pri thread pool
     USER,  // User thread (Non-RocksDB BG thread)
+    BOTTOM_PRIORITY,  // RocksDB BG thread in bottom-pri thread pool
     NUM_THREAD_TYPES
   };
 
@@ -163,7 +164,7 @@ struct ThreadStatus {
   // The followings are a set of utility functions for interpreting
   // the information of ThreadStatus
 
-  static const std::string& GetThreadTypeName(ThreadType thread_type);
+  static std::string GetThreadTypeName(ThreadType thread_type);
 
   // Obtain the name of an operation given its type.
   static const std::string& GetOperationName(OperationType op_type);

monitoring/thread_status_impl.cc

@@ -14,14 +14,21 @@
 namespace rocksdb {
 
 #ifdef ROCKSDB_USING_THREAD_STATUS
-const std::string& ThreadStatus::GetThreadTypeName(
+std::string ThreadStatus::GetThreadTypeName(
     ThreadStatus::ThreadType thread_type) {
-  static std::string thread_type_names[NUM_THREAD_TYPES + 1] = {
-      "High Pri", "Low Pri", "User", "Unknown"};
-  if (thread_type < 0 || thread_type >= NUM_THREAD_TYPES) {
-    return thread_type_names[NUM_THREAD_TYPES];  // "Unknown"
+  switch (thread_type) {
+    case ThreadStatus::ThreadType::HIGH_PRIORITY:
+      return "High Pri";
+    case ThreadStatus::ThreadType::LOW_PRIORITY:
+      return "Low Pri";
+    case ThreadStatus::ThreadType::USER:
+      return "User";
+    case ThreadStatus::ThreadType::BOTTOM_PRIORITY:
+      return "Bottom Pri";
+    case ThreadStatus::ThreadType::NUM_THREAD_TYPES:
+      assert(false);
   }
-  return thread_type_names[thread_type];
+  return "Unknown";
 }
 
 const std::string& ThreadStatus::GetOperationName(
@@ -120,7 +127,7 @@ std::map<std::string, uint64_t>
 
 #else
 
-const std::string& ThreadStatus::GetThreadTypeName(
+std::string ThreadStatus::GetThreadTypeName(
     ThreadStatus::ThreadType thread_type) {
   static std::string dummy_str = "";
   return dummy_str;

util/threadpool_imp.cc

@@ -254,11 +254,25 @@ void* ThreadPoolImpl::Impl::BGThreadWrapper(void* arg) {
   size_t thread_id = meta->thread_id_;
   ThreadPoolImpl::Impl* tp = meta->thread_pool_;
 #ifdef ROCKSDB_USING_THREAD_STATUS
-  // for thread-status
-  ThreadStatusUtil::RegisterThread(
-      tp->GetHostEnv(), (tp->GetThreadPriority() == Env::Priority::HIGH
-                             ? ThreadStatus::HIGH_PRIORITY
-                             : ThreadStatus::LOW_PRIORITY));
+  // initialize it because compiler isn't good enough to see we don't use it
+  // uninitialized
+  ThreadStatus::ThreadType thread_type = ThreadStatus::NUM_THREAD_TYPES;
+  switch (tp->GetThreadPriority()) {
+    case Env::Priority::HIGH:
+      thread_type = ThreadStatus::HIGH_PRIORITY;
+      break;
+    case Env::Priority::LOW:
+      thread_type = ThreadStatus::LOW_PRIORITY;
+      break;
+    case Env::Priority::BOTTOM:
+      thread_type = ThreadStatus::BOTTOM_PRIORITY;
+      break;
+    case Env::Priority::TOTAL:
+      assert(false);
+      return nullptr;
+  }
+  assert(thread_type != ThreadStatus::NUM_THREAD_TYPES);
+  ThreadStatusUtil::RegisterThread(tp->GetHostEnv(), thread_type);
 #endif
   delete meta;
   tp->BGThread(thread_id);