Redesign pending_outputs_

Summary:
Here's a prototype of redesigning pending_outputs_. This way, we don't have to expose pending_outputs_ to other classes (CompactionJob, FlushJob, MemtableList). DBImpl takes care of it.

Still have to write some comments, but should be good enough to start the discussion.

Test Plan: make check, will also run stress test

Reviewers: ljin, sdong, rven, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28353

db/compaction_job.cc

@@ -205,10 +205,9 @@ CompactionJob::CompactionJob(
     Compaction* compaction, const DBOptions& db_options,
     const MutableCFOptions& mutable_cf_options, const EnvOptions& env_options,
     VersionSet* versions, port::Mutex* db_mutex,
-    std::atomic<bool>* shutting_down, FileNumToPathIdMap* pending_outputs,
-    LogBuffer* log_buffer, Directory* db_directory, Statistics* stats,
-    SnapshotList* snapshots, bool is_snapshot_supported,
-    std::shared_ptr<Cache> table_cache,
+    std::atomic<bool>* shutting_down, LogBuffer* log_buffer,
+    Directory* db_directory, Statistics* stats, SnapshotList* snapshots,
+    bool is_snapshot_supported, std::shared_ptr<Cache> table_cache,
     std::function<uint64_t()> yield_callback)
     : compact_(new CompactionState(compaction)),
       compaction_stats_(1),
@@ -219,7 +218,6 @@ CompactionJob::CompactionJob(
       versions_(versions),
       db_mutex_(db_mutex),
       shutting_down_(shutting_down),
-      pending_outputs_(pending_outputs),
       log_buffer_(log_buffer),
       db_directory_(db_directory),
       stats_(stats),
@@ -469,10 +467,6 @@ Status CompactionJob::Install(Status status) {
   cfd->internal_stats()->AddCompactionStats(
       compact_->compaction->output_level(), compaction_stats_);
 
-  // if there were any unused file number (mostly in case of
-  // compaction error), free up the entry from pending_putputs
-  ReleaseCompactionUnusedFileNumbers();
-
   if (status.ok()) {
     status = InstallCompactionResults();
   }
@@ -511,8 +505,6 @@ void CompactionJob::AllocateCompactionOutputFileNumbers() {
   int filesNeeded = compact_->compaction->num_input_files(1);
   for (int i = 0; i < std::max(filesNeeded, 1); i++) {
     uint64_t file_number = versions_->NewFileNumber();
-    pending_outputs_->insert(
-        {file_number, compact_->compaction->GetOutputPathId()});
     compact_->allocated_file_numbers.push_back(file_number);
   }
 }
@@ -1041,14 +1033,6 @@ void CompactionJob::RecordCompactionIOStats() {
   IOSTATS_RESET(bytes_written);
 }
 
-// Frees up unused file number.
-void CompactionJob::ReleaseCompactionUnusedFileNumbers() {
-  db_mutex_->AssertHeld();
-  for (const auto file_number : compact_->allocated_file_numbers) {
-    pending_outputs_->erase(file_number);
-  }
-}
-
 Status CompactionJob::OpenCompactionOutputFile() {
   assert(compact_ != nullptr);
   assert(compact_->builder == nullptr);
@@ -1061,9 +1045,10 @@ Status CompactionJob::OpenCompactionOutputFile() {
     compact_->allocated_file_numbers.pop_front();
   } else {
     db_mutex_->Lock();
+    // TODO(icanadi) make Versions::next_file_number_ atomic and remove db_lock
+    // around here. Once we do that, AllocateCompactionOutputFileNumbers() will
+    // not be needed.
     file_number = versions_->NewFileNumber();
-    pending_outputs_->insert(
-        {file_number, compact_->compaction->GetOutputPathId()});
     db_mutex_->Unlock();
   }
   // Make the output file
@@ -1112,7 +1097,6 @@ void CompactionJob::CleanupCompaction(Status status) {
   }
   for (size_t i = 0; i < compact_->outputs.size(); i++) {
     const CompactionState::Output& out = compact_->outputs[i];
-    pending_outputs_->erase(out.number);
 
     // If this file was inserted into the table cache then remove
     // them here because this compaction was not committed.

db/compaction_job.h

@@ -57,10 +57,9 @@ class CompactionJob {
                 const MutableCFOptions& mutable_cf_options,
                 const EnvOptions& env_options, VersionSet* versions,
                 port::Mutex* db_mutex, std::atomic<bool>* shutting_down,
-                FileNumToPathIdMap* pending_outputs, LogBuffer* log_buffer,
-                Directory* db_directory, Statistics* stats,
-                SnapshotList* snapshot_list, bool is_snapshot_supported,
-                std::shared_ptr<Cache> table_cache,
+                LogBuffer* log_buffer, Directory* db_directory,
+                Statistics* stats, SnapshotList* snapshot_list,
+                bool is_snapshot_supported, std::shared_ptr<Cache> table_cache,
                 std::function<uint64_t()> yield_callback);
 
   ~CompactionJob() { assert(compact_ == nullptr); }
@@ -92,7 +91,6 @@ class CompactionJob {
       SequenceNumber in, const std::vector<SequenceNumber>& snapshots,
       SequenceNumber* prev_snapshot);
   void RecordCompactionIOStats();
-  void ReleaseCompactionUnusedFileNumbers();
   Status OpenCompactionOutputFile();
   void CleanupCompaction(Status status);
 
@@ -115,7 +113,6 @@ class CompactionJob {
   VersionSet* versions_;
   port::Mutex* db_mutex_;
   std::atomic<bool>* shutting_down_;
-  FileNumToPathIdMap* pending_outputs_;
   LogBuffer* log_buffer_;
   Directory* db_directory_;
   Statistics* stats_;

db/db_impl.cc

@@ -443,8 +443,11 @@ void DBImpl::FindObsoleteFiles(JobContext* job_context, bool force,
   }
 
   // don't delete live files
-  for (auto pair : pending_outputs_) {
-    job_context->sst_live.emplace_back(pair.first, pair.second, 0);
+  if (pending_outputs_.size()) {
+    job_context->min_pending_output = *pending_outputs_.begin();
+  } else {
+    // delete all of them
+    job_context->min_pending_output = std::numeric_limits<uint64_t>::max();
   }
   versions_->AddLiveFiles(&job_context->sst_live);
 
@@ -567,7 +570,10 @@ void DBImpl::PurgeObsoleteFiles(const JobContext& state) {
         keep = (number >= state.manifest_file_number);
         break;
       case kTableFile:
-        keep = (sst_live_map.find(number) != sst_live_map.end());
+        // If the second condition is not there, this makes
+        // DontDeletePendingOutputs fail
+        keep = (sst_live_map.find(number) != sst_live_map.end()) ||
+               number >= state.min_pending_output;
         break;
       case kTempFile:
         // Any temp files that are currently being written to must
@@ -981,7 +987,8 @@ Status DBImpl::WriteLevel0TableForRecovery(ColumnFamilyData* cfd, MemTable* mem,
   const uint64_t start_micros = env_->NowMicros();
   FileMetaData meta;
   meta.fd = FileDescriptor(versions_->NewFileNumber(), 0, 0);
-  pending_outputs_[meta.fd.GetNumber()] = 0;  // path 0 for level 0 file.
+  auto pending_outputs_inserted_elem =
+      CaptureCurrentFileNumberInPendingOutputs();
   ReadOptions ro;
   ro.total_order_seek = true;
   Arena arena;
@@ -1013,7 +1020,7 @@ Status DBImpl::WriteLevel0TableForRecovery(ColumnFamilyData* cfd, MemTable* mem,
         cfd->GetName().c_str(), meta.fd.GetNumber(), meta.fd.GetFileSize(),
         s.ToString().c_str());
   }
-  pending_outputs_.erase(meta.fd.GetNumber());
+  ReleaseFileNumberFromPendingOutputs(pending_outputs_inserted_elem);
 
   // Note that if file_size is zero, the file has been deleted and
   // should not be added to the manifest.
@@ -1044,9 +1051,9 @@ Status DBImpl::FlushMemTableToOutputFile(
 
   FlushJob flush_job(dbname_, cfd, db_options_, mutable_cf_options,
                      env_options_, versions_.get(), &mutex_, &shutting_down_,
-                     &pending_outputs_, snapshots_.GetNewest(), job_context,
-                     log_buffer, db_directory_.get(),
-                     GetCompressionFlush(*cfd->ioptions()), stats_);
+                     snapshots_.GetNewest(), job_context, log_buffer,
+                     db_directory_.get(), GetCompressionFlush(*cfd->ioptions()),
+                     stats_);
 
   Status s = flush_job.Run();
 
@@ -1550,6 +1557,9 @@ void DBImpl::BackgroundCallFlush() {
   {
     MutexLock l(&mutex_);
 
+    auto pending_outputs_inserted_elem =
+        CaptureCurrentFileNumberInPendingOutputs();
+
     Status s;
     if (!shutting_down_.load(std::memory_order_acquire)) {
       s = BackgroundFlush(&madeProgress, &job_context, &log_buffer);
@@ -1573,6 +1583,8 @@ void DBImpl::BackgroundCallFlush() {
       }
     }
 
+    ReleaseFileNumberFromPendingOutputs(pending_outputs_inserted_elem);
+
     // If !s.ok(), this means that Flush failed. In that case, we want
     // to delete all obsolete files and we force FindObsoleteFiles()
     FindObsoleteFiles(&job_context, !s.ok());
@@ -1616,6 +1628,10 @@ void DBImpl::BackgroundCallCompaction() {
   LogBuffer log_buffer(InfoLogLevel::INFO_LEVEL, db_options_.info_log.get());
   {
     MutexLock l(&mutex_);
+
+    auto pending_outputs_inserted_elem =
+        CaptureCurrentFileNumberInPendingOutputs();
+
     assert(bg_compaction_scheduled_);
     Status s;
     if (!shutting_down_.load(std::memory_order_acquire)) {
@@ -1640,6 +1656,8 @@ void DBImpl::BackgroundCallCompaction() {
       }
     }
 
+    ReleaseFileNumberFromPendingOutputs(pending_outputs_inserted_elem);
+
     // If !s.ok(), this means that Compaction failed. In that case, we want
     // to delete all obsolete files we might have created and we force
     // FindObsoleteFiles(). This is because job_context does not
@@ -1848,9 +1866,9 @@ Status DBImpl::BackgroundCompaction(bool* madeProgress, JobContext* job_context,
     };
     CompactionJob compaction_job(
         c.get(), db_options_, *c->mutable_cf_options(), env_options_,
-        versions_.get(), &mutex_, &shutting_down_, &pending_outputs_,
-        log_buffer, db_directory_.get(), stats_, &snapshots_,
-        IsSnapshotSupported(), table_cache_, std::move(yield_callback));
+        versions_.get(), &mutex_, &shutting_down_, log_buffer,
+        db_directory_.get(), stats_, &snapshots_, IsSnapshotSupported(),
+        table_cache_, std::move(yield_callback));
     compaction_job.Prepare();
     mutex_.Unlock();
     status = compaction_job.Run();
@@ -2968,6 +2986,22 @@ void DBImpl::GetApproximateSizes(ColumnFamilyHandle* column_family,
   }
 }
 
+std::list<uint64_t>::iterator
+DBImpl::CaptureCurrentFileNumberInPendingOutputs() {
+  // We need to remember the iterator of our insert, because after the
+  // background job is done, we need to remove that element from
+  // pending_outputs_.
+  pending_outputs_.push_back(versions_->current_next_file_number());
+  auto pending_outputs_inserted_elem = pending_outputs_.end();
+  --pending_outputs_inserted_elem;
+  return pending_outputs_inserted_elem;
+}
+
+void DBImpl::ReleaseFileNumberFromPendingOutputs(
+    std::list<uint64_t>::iterator v) {
+  pending_outputs_.erase(v);
+}
+
 #ifndef ROCKSDB_LITE
 Status DBImpl::GetUpdatesSince(
     SequenceNumber seq, unique_ptr<TransactionLogIterator>* iter,

db/db_impl.h

@@ -12,6 +12,7 @@
 #include <deque>
 #include <limits>
 #include <set>
+#include <list>
 #include <utility>
 #include <vector>
 #include <string>
@@ -265,6 +266,24 @@ class DBImpl : public DB {
   // Delete any unneeded files and stale in-memory entries.
   void DeleteObsoleteFiles();
 
+  // Background process needs to call
+  //     auto x = CaptureCurrentFileNumberInPendingOutputs()
+  //     <do something>
+  //     ReleaseFileNumberFromPendingOutputs(x)
+  // This will protect any temporary files created while <do something> is
+  // executing from being deleted.
+  // -----------
+  // This function will capture current file number and append it to
+  // pending_outputs_. This will prevent any background process to delete any
+  // file created after this point.
+  std::list<uint64_t>::iterator CaptureCurrentFileNumberInPendingOutputs();
+  // This function should be called with the result of
+  // CaptureCurrentFileNumberInPendingOutputs(). It then marks that any file
+  // created between the calls CaptureCurrentFileNumberInPendingOutputs() and
+  // ReleaseFileNumberFromPendingOutputs() can now be deleted (if it's not live
+  // and blocked by any other pending_outputs_ calls)
+  void ReleaseFileNumberFromPendingOutputs(std::list<uint64_t>::iterator v);
+
   // Flush the in-memory write buffer to storage.  Switches to a new
   // log-file/memtable and writes a new descriptor iff successful.
   Status FlushMemTableToOutputFile(ColumnFamilyData* cfd,
@@ -390,10 +409,16 @@ class DBImpl : public DB {
 
   SnapshotList snapshots_;
 
-  // Set of table files to protect from deletion because they are
-  // part of ongoing compactions.
-  // map from pending file number ID to their path IDs.
-  FileNumToPathIdMap pending_outputs_;
+  // For each background job, pending_outputs_ keeps the current file number at
+  // the time that background job started.
+  // FindObsoleteFiles()/PurgeObsoleteFiles() never deletes any file that has
+  // number bigger than any of the file number in pending_outputs_. Since file
+  // numbers grow monotonically, this also means that pending_outputs_ is always
+  // sorted. After a background job is done executing, its file number is
+  // deleted from pending_outputs_, which allows PurgeObsoleteFiles() to clean
+  // it up.
+  // State is protected with db mutex.
+  std::list<uint64_t> pending_outputs_;
 
   // At least one compaction or flush job is pending but not yet scheduled
   // because of the max background thread limit.

db/db_test.cc

@@ -165,6 +165,8 @@ class SpecialEnv : public EnvWrapper {
 
   std::atomic<uint32_t> non_writable_count_;
 
+  std::function<void()>* table_write_callback_;
+
   explicit SpecialEnv(Env* base) : EnvWrapper(base), rnd_(301) {
     delay_sstable_sync_.store(false, std::memory_order_release);
     drop_writes_.store(false, std::memory_order_release);
@@ -181,6 +183,8 @@ class SpecialEnv : public EnvWrapper {
     non_writeable_rate_ = 0;
     new_writable_count_ = 0;
     non_writable_count_ = 0;
+    periodic_non_writable_ = 0;
+    table_write_callback_ = nullptr;
   }
 
   Status NewWritableFile(const std::string& f, unique_ptr<WritableFile>* r,
@@ -196,6 +200,9 @@ class SpecialEnv : public EnvWrapper {
             base_(std::move(base)) {
       }
       Status Append(const Slice& data) {
+        if (env_->table_write_callback_) {
+          (*env_->table_write_callback_)();
+        }
         if (env_->drop_writes_.load(std::memory_order_acquire)) {
           // Drop writes on the floor
           return Status::OK();
@@ -9042,6 +9049,38 @@ TEST(DBTest, DynamicMiscOptions) {
   assert_reseek_count(300, 1);
 }
 
+TEST(DBTest, DontDeletePendingOutputs) {
+  Options options;
+  options.env = env_;
+  options.create_if_missing = true;
+  DestroyAndReopen(options);
+
+  // Every time we write to a table file, call FOF/POF with full DB scan. This
+  // will make sure our pending_outputs_ protection work correctly
+  std::function<void()> purge_obsolete_files_function = [&]() {
+    JobContext job_context;
+    dbfull()->TEST_LockMutex();
+    dbfull()->FindObsoleteFiles(&job_context, true /*force*/);
+    dbfull()->TEST_UnlockMutex();
+    dbfull()->PurgeObsoleteFiles(job_context);
+  };
+
+  env_->table_write_callback_ = &purge_obsolete_files_function;
+
+  for (int i = 0; i < 2; ++i) {
+    ASSERT_OK(Put("a", "begin"));
+    ASSERT_OK(Put("z", "end"));
+    ASSERT_OK(Flush());
+  }
+
+  // If pending output guard does not work correctly, PurgeObsoleteFiles() will
+  // delete the file that Compaction is trying to create, causing this: error
+  // db/db_test.cc:975: IO error:
+  // /tmp/rocksdbtest-1552237650/db_test/000009.sst: No such file or directory
+  Compact("a", "b");
+}
+
+
 }  // namespace rocksdb
 
 int main(int argc, char** argv) {

db/filename.h

@@ -36,9 +36,6 @@ enum FileType {
   kIdentityFile
 };
 
-// map from file number to path ID.
-typedef std::unordered_map<uint64_t, uint32_t> FileNumToPathIdMap;
-
 // Return the name of the log file with the specified number
 // in the db named by "dbname".  The result will be prefixed with
 // "dbname".

db/flush_job.cc

@@ -55,7 +55,6 @@ FlushJob::FlushJob(const std::string& dbname, ColumnFamilyData* cfd,
                    const MutableCFOptions& mutable_cf_options,
                    const EnvOptions& env_options, VersionSet* versions,
                    port::Mutex* db_mutex, std::atomic<bool>* shutting_down,
-                   FileNumToPathIdMap* pending_outputs,
                    SequenceNumber newest_snapshot, JobContext* job_context,
                    LogBuffer* log_buffer, Directory* db_directory,
                    CompressionType output_compression, Statistics* stats)
@@ -67,7 +66,6 @@ FlushJob::FlushJob(const std::string& dbname, ColumnFamilyData* cfd,
       versions_(versions),
       db_mutex_(db_mutex),
       shutting_down_(shutting_down),
-      pending_outputs_(pending_outputs),
       newest_snapshot_(newest_snapshot),
       job_context_(job_context),
       log_buffer_(log_buffer),
@@ -107,13 +105,12 @@ Status FlushJob::Run() {
   }
 
   if (!s.ok()) {
-    cfd_->imm()->RollbackMemtableFlush(mems, file_number, pending_outputs_);
+    cfd_->imm()->RollbackMemtableFlush(mems, file_number);
   } else {
     // Replace immutable memtable with the generated Table
     s = cfd_->imm()->InstallMemtableFlushResults(
         cfd_, mutable_cf_options_, mems, versions_, db_mutex_, file_number,
-        pending_outputs_, &job_context_->memtables_to_free, db_directory_,
-        log_buffer_);
+        &job_context_->memtables_to_free, db_directory_, log_buffer_);
   }
 
   return s;
@@ -128,7 +125,6 @@ Status FlushJob::WriteLevel0Table(const autovector<MemTable*>& mems,
   meta.fd = FileDescriptor(versions_->NewFileNumber(), 0, 0);
   *filenumber = meta.fd.GetNumber();
   // path 0 for level 0 file.
-  pending_outputs_->insert({meta.fd.GetNumber(), 0});
 
   const SequenceNumber earliest_seqno_in_memtable =
       mems[0]->GetFirstSequenceNumber();
@@ -180,15 +176,6 @@ Status FlushJob::WriteLevel0Table(const autovector<MemTable*>& mems,
   // re-acquire the most current version
   base = cfd_->current();
 
-  // There could be multiple threads writing to its own level-0 file.
-  // The pending_outputs cannot be cleared here, otherwise this newly
-  // created file might not be considered as a live-file by another
-  // compaction thread that is concurrently deleting obselete files.
-  // The pending_outputs can be cleared only after the new version is
-  // committed so that other threads can recognize this file as a
-  // valid one.
-  // pending_outputs_.erase(meta.number);
-
   // Note that if file_size is zero, the file has been deleted and
   // should not be added to the manifest.
   int level = 0;

db/flush_job.h

@@ -55,10 +55,9 @@ class FlushJob {
            const MutableCFOptions& mutable_cf_options,
            const EnvOptions& env_options, VersionSet* versions,
            port::Mutex* db_mutex, std::atomic<bool>* shutting_down,
-           FileNumToPathIdMap* pending_outputs, SequenceNumber newest_snapshot,
-           JobContext* job_context, LogBuffer* log_buffer,
-           Directory* db_directory, CompressionType output_compression,
-           Statistics* stats);
+           SequenceNumber newest_snapshot, JobContext* job_context,
+           LogBuffer* log_buffer, Directory* db_directory,
+           CompressionType output_compression, Statistics* stats);
   ~FlushJob() {}
 
   Status Run();
@@ -74,7 +73,6 @@ class FlushJob {
   VersionSet* versions_;
   port::Mutex* db_mutex_;
   std::atomic<bool>* shutting_down_;
-  FileNumToPathIdMap* pending_outputs_;
   SequenceNumber newest_snapshot_;
   JobContext* job_context_;
   LogBuffer* log_buffer_;

db/flush_job_test.cc

@@ -73,7 +73,6 @@ class FlushJobTest {
   std::unique_ptr<VersionSet> versions_;
   port::Mutex mutex_;
   std::atomic<bool> shutting_down_;
-  FileNumToPathIdMap pending_outputs_;
   std::shared_ptr<MockTableFactory> mock_table_factory_;
 };
 
@@ -83,8 +82,8 @@ TEST(FlushJobTest, Empty) {
   FlushJob flush_job(dbname_, versions_->GetColumnFamilySet()->GetDefault(),
                      db_options_, *cfd->GetLatestMutableCFOptions(),
                      env_options_, versions_.get(), &mutex_, &shutting_down_,
-                     &pending_outputs_, SequenceNumber(), &job_context, nullptr,
-                     nullptr, kNoCompression, nullptr);
+                     SequenceNumber(), &job_context, nullptr, nullptr,
+                     kNoCompression, nullptr);
   ASSERT_OK(flush_job.Run());
 }
 
@@ -108,8 +107,8 @@ TEST(FlushJobTest, NonEmpty) {
   FlushJob flush_job(dbname_, versions_->GetColumnFamilySet()->GetDefault(),
                      db_options_, *cfd->GetLatestMutableCFOptions(),
                      env_options_, versions_.get(), &mutex_, &shutting_down_,
-                     &pending_outputs_, SequenceNumber(), &job_context, nullptr,
-                     nullptr, kNoCompression, nullptr);
+                     SequenceNumber(), &job_context, nullptr, nullptr,
+                     kNoCompression, nullptr);
   mutex_.Lock();
   ASSERT_OK(flush_job.Run());
   mutex_.Unlock();

db/job_context.h

@@ -58,8 +58,12 @@ struct JobContext {
 
   // the current manifest_file_number, log_number and prev_log_number
   // that corresponds to the set of files in 'live'.
-  uint64_t manifest_file_number, pending_manifest_file_number, log_number,
-      prev_log_number;
+  uint64_t manifest_file_number;
+  uint64_t pending_manifest_file_number;
+  uint64_t log_number;
+  uint64_t prev_log_number;
+
+  uint64_t min_pending_output = 0;
 
   explicit JobContext(bool create_superversion = false) {
     manifest_file_number = 0;

db/memtable_list.cc

@@ -144,8 +144,7 @@ void MemTableList::PickMemtablesToFlush(autovector<MemTable*>* ret) {
 }
 
 void MemTableList::RollbackMemtableFlush(const autovector<MemTable*>& mems,
-                                         uint64_t file_number,
-                                         FileNumToPathIdMap* pending_outputs) {
+                                         uint64_t file_number) {
   assert(!mems.empty());
 
   // If the flush was not successful, then just reset state.
@@ -159,7 +158,6 @@ void MemTableList::RollbackMemtableFlush(const autovector<MemTable*>& mems,
     m->edit_.Clear();
     num_flush_not_started_++;
   }
-  pending_outputs->erase(file_number);
   imm_flush_needed.store(true, std::memory_order_release);
 }
 
@@ -167,9 +165,8 @@ void MemTableList::RollbackMemtableFlush(const autovector<MemTable*>& mems,
 Status MemTableList::InstallMemtableFlushResults(
     ColumnFamilyData* cfd, const MutableCFOptions& mutable_cf_options,
     const autovector<MemTable*>& mems, VersionSet* vset, port::Mutex* mu,
-    uint64_t file_number, FileNumToPathIdMap* pending_outputs,
-    autovector<MemTable*>* to_delete, Directory* db_directory,
-    LogBuffer* log_buffer) {
+    uint64_t file_number, autovector<MemTable*>* to_delete,
+    Directory* db_directory, LogBuffer* log_buffer) {
   mu->AssertHeld();
 
   // flush was sucessful
@@ -220,11 +217,6 @@ Status MemTableList::InstallMemtableFlushResults(
         current_->Remove(m);
         assert(m->file_number_ > 0);
 
-        // pending_outputs can be cleared only after the newly created file
-        // has been written to a committed version so that other concurrently
-        // executing compaction threads do not mistakenly assume that this
-        // file is not live.
-        pending_outputs->erase(m->file_number_);
         if (m->Unref() != nullptr) {
           to_delete->push_back(m);
         }
@@ -237,7 +229,6 @@ Status MemTableList::InstallMemtableFlushResults(
         m->flush_in_progress_ = false;
         m->edit_.Clear();
         num_flush_not_started_++;
-        pending_outputs->erase(m->file_number_);
         m->file_number_ = 0;
         imm_flush_needed.store(true, std::memory_order_release);
       }

db/memtable_list.h

@@ -108,16 +108,14 @@ class MemTableList {
   // Reset status of the given memtable list back to pending state so that
   // they can get picked up again on the next round of flush.
   void RollbackMemtableFlush(const autovector<MemTable*>& mems,
-                             uint64_t file_number,
-                             FileNumToPathIdMap* pending_outputs);
+                             uint64_t file_number);
 
   // Commit a successful flush in the manifest file
   Status InstallMemtableFlushResults(
       ColumnFamilyData* cfd, const MutableCFOptions& mutable_cf_options,
       const autovector<MemTable*>& m, VersionSet* vset, port::Mutex* mu,
-      uint64_t file_number, FileNumToPathIdMap* pending_outputs,
-      autovector<MemTable*>* to_delete, Directory* db_directory,
-      LogBuffer* log_buffer);
+      uint64_t file_number, autovector<MemTable*>* to_delete,
+      Directory* db_directory, LogBuffer* log_buffer);
 
   // New memtables are inserted at the front of the list.
   // Takes ownership of the referenced held on *m by the caller of Add().

db/version_set.h

@@ -530,6 +530,9 @@ class VersionSet {
     return pending_manifest_file_number_;
   }
 
+  // REQUIRED: mutex locked
+  uint64_t current_next_file_number() const { return next_file_number_; }
+
   // Allocate and return a new file number
   uint64_t NewFileNumber() { return next_file_number_++; }