Optimize usage of Status in CompactionJob

Summary: Based on @ljin feedback

Test Plan: compiles

Reviewers: ljin, yhchiang, sdong

Reviewed By: sdong

Subscribers: ljin, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28515

db/compaction_job.cc

@@ -455,14 +455,14 @@ Status CompactionJob::Run() {
   return status;
 }
 
-Status CompactionJob::Install(Status status, port::Mutex* db_mutex) {
+void CompactionJob::Install(Status* status, port::Mutex* db_mutex) {
   db_mutex->AssertHeld();
   ColumnFamilyData* cfd = compact_->compaction->column_family_data();
   cfd->internal_stats()->AddCompactionStats(
       compact_->compaction->output_level(), compaction_stats_);
 
-  if (status.ok()) {
-    status = InstallCompactionResults(db_mutex);
+  if (status->ok()) {
+    *status = InstallCompactionResults(db_mutex);
   }
   VersionStorageInfo::LevelSummaryStorage tmp;
   const auto& stats = compaction_stats_;
@@ -483,11 +483,10 @@ Status CompactionJob::Install(Status status, port::Mutex* db_mutex) {
               (stats.bytes_written + stats.bytes_readnp1 + stats.bytes_readn) /
                   static_cast<double>(stats.bytes_readn),
               stats.bytes_written / static_cast<double>(stats.bytes_readn),
-              status.ToString().c_str(), stats.num_input_records,
+              status->ToString().c_str(), stats.num_input_records,
               stats.num_dropped_records);
 
-  CleanupCompaction(status);
-  return status;
+  CleanupCompaction(*status);
 }
 
 Status CompactionJob::ProcessKeyValueCompaction(int64_t* imm_micros,
@@ -1054,7 +1053,7 @@ Status CompactionJob::OpenCompactionOutputFile() {
   return s;
 }
 
-void CompactionJob::CleanupCompaction(Status status) {
+void CompactionJob::CleanupCompaction(const Status& status) {
   if (compact_->builder != nullptr) {
     // May happen if we get a shutdown call in the middle of compaction
     compact_->builder->Abandon();

db/compaction_job.h

@@ -75,7 +75,7 @@ class CompactionJob {
   Status Run();
   // REQUIRED: mutex held
   // status is the return of Run()
-  Status Install(Status status, port::Mutex* db_mutex);
+  void Install(Status* status, port::Mutex* db_mutex);
 
  private:
   void AllocateCompactionOutputFileNumbers();
@@ -92,7 +92,7 @@ class CompactionJob {
       SequenceNumber* prev_snapshot);
   void RecordCompactionIOStats();
   Status OpenCompactionOutputFile();
-  void CleanupCompaction(Status status);
+  void CleanupCompaction(const Status& status);
 
   // CompactionJob state
   struct CompactionState;

db/db_impl.cc

@@ -1295,13 +1295,11 @@ Status DBImpl::CompactFilesImpl(
   mutex_.Unlock();
   Status status = compaction_job.Run();
   mutex_.Lock();
-  if (status.ok()) {
-    status = compaction_job.Install(status, &mutex_);
+  compaction_job.Install(&status, &mutex_);
   if (status.ok()) {
     InstallSuperVersionBackground(c->column_family_data(), &job_context,
                                   *c->mutable_cf_options());
   }
-  }
   c->ReleaseCompactionFiles(s);
   c->ReleaseInputs();
   c.reset();
@@ -2070,7 +2068,7 @@ Status DBImpl::BackgroundCompaction(bool* madeProgress, JobContext* job_context,
     mutex_.Unlock();
     status = compaction_job.Run();
     mutex_.Lock();
-    status = compaction_job.Install(status, &mutex_);
+    compaction_job.Install(&status, &mutex_);
     if (status.ok()) {
       InstallSuperVersionBackground(c->column_family_data(), job_context,
                                     *c->mutable_cf_options());