Fixed the tsan failure in util/compaction_job_stats_impl.cc

Summary:
The type of smallest_output_key_prefix and largest_output_key_prefix
have been changed to std::string in https://reviews.facebook.net/D39537.
As a result, we shouldn't do smallest_output_key_prefix[0] = 0 in the
initialization.

Test Plan: compile db_test with tsan enabled and repeat DBTest.CompactionDeletionTrigger test to verify the tsan issue has been gone.

Reviewers: igor, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D39645

db/db_impl.cc

@@ -1736,6 +1736,9 @@ Status DBImpl::ReFitLevel(ColumnFamilyData* cfd, int level, int target_level) {
     to_level = FindMinimumEmptyLevelFitting(cfd, mutable_cf_options, level);
   }
 
+  printf("level %d, to_level %d\n", level, to_level);
+  assert(to_level <= level);
+
   Status status;
   auto* vstorage = cfd->current()->storage_info();
   if (to_level > level) {

db/db_test.cc

@@ -13238,6 +13238,57 @@ TEST_F(DBTest, FlushesInParallelWithCompactRange) {
     rocksdb::SyncPoint::GetInstance()->DisableProcessing();
   }
 }
+TEST_F(DBTest, TrivialMoveTargetLevel) {
+  int32_t trivial_move = 0;
+  int32_t non_trivial_move = 0;
+/*
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "DBImpl::BackgroundCompaction:TrivialMove",
+      [&](void* arg) { trivial_move++;printf("trivial\n"); });
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "DBImpl::BackgroundCompaction:NonTrivial",
+      [&](void* arg) { non_trivial_move++;printf("non-trivial\n"); });
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+*/
+  Options options = CurrentOptions();
+  options.disable_auto_compactions = true;
+  options.write_buffer_size = 10 * 1024 * 1024;
+  options.num_levels = 5;
+
+  DestroyAndReopen(options);
+  int32_t value_size = 10 * 1024;  // 10 KB
+
+  // Add 2 non-overlapping files
+  Random rnd(301);
+  std::map<int32_t, std::string> values;
+  for (int32_t i = 0; i <= 100; i++) {
+    values[i] = RandomString(&rnd, value_size);
+    ASSERT_OK(Put(Key(i), values[i]));
+  }
+  ASSERT_OK(Flush());
+
+  for (int32_t i = 300; i <= 700; i++) {
+    values[i] = RandomString(&rnd, value_size);
+    ASSERT_OK(Put(Key(i), values[i]));
+  }
+  ASSERT_OK(Flush());
+
+  ASSERT_EQ("2", FilesPerLevel(0));
+  printf("Compact\n");
+  db_->CompactRange(db_->DefaultColumnFamily(), nullptr, nullptr, true, 1, 0);
+  printf("Done\n");
+  ASSERT_EQ("0,0,0,2", FilesPerLevel(0));
+
+  ASSERT_EQ(trivial_move, 3);
+  ASSERT_EQ(non_trivial_move, 0);
+
+  for (int32_t i = 0; i <= 100; i++) {
+    ASSERT_EQ(Get(Key(i)), values[i]);
+  }
+  for (int32_t i = 300; i <= 700; i++) {
+    ASSERT_EQ(Get(Key(i)), values[i]);
+  }
+}
 
 }  // namespace rocksdb
 

util/compaction_job_stats_impl.cc

@@ -29,9 +29,6 @@ void CompactionJobStats::Reset() {
   num_records_replaced = 0;
 
   is_manual_compaction = 0;
-
-  smallest_output_key_prefix[0] = 0;
-  largest_output_key_prefix[0] = 0;
 }
 
 #else