Adding upstream version 14.2.21.upstream/14.2.21upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2974 insertions, 0 deletions

diff --git a/src/rocksdb/db/db_impl_compaction_flush.cc b/src/rocksdb/db/db_impl_compaction_flush.cc
new file mode 100644
index 00000000..f208b873
--- /dev/null
+++ b/src/rocksdb/db/db_impl_compaction_flush.cc
@@ -0,0 +1,2974 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+#include "db/db_impl.h"
+
+#ifndef __STDC_FORMAT_MACROS
+#define __STDC_FORMAT_MACROS
+#endif
+#include <inttypes.h>
+
+#include "db/builder.h"
+#include "db/error_handler.h"
+#include "db/event_helpers.h"
+#include "monitoring/iostats_context_imp.h"
+#include "monitoring/perf_context_imp.h"
+#include "monitoring/thread_status_updater.h"
+#include "monitoring/thread_status_util.h"
+#include "util/concurrent_task_limiter_impl.h"
+#include "util/sst_file_manager_impl.h"
+#include "util/sync_point.h"
+
+namespace rocksdb {
+
+bool DBImpl::EnoughRoomForCompaction(
+    ColumnFamilyData* cfd, const std::vector<CompactionInputFiles>& inputs,
+    bool* sfm_reserved_compact_space, LogBuffer* log_buffer) {
+  // Check if we have enough room to do the compaction
+  bool enough_room = true;
+#ifndef ROCKSDB_LITE
+  auto sfm = static_cast<SstFileManagerImpl*>(
+      immutable_db_options_.sst_file_manager.get());
+  if (sfm) {
+    // Pass the current bg_error_ to SFM so it can decide what checks to
+    // perform. If this DB instance hasn't seen any error yet, the SFM can be
+    // optimistic and not do disk space checks
+    enough_room =
+        sfm->EnoughRoomForCompaction(cfd, inputs, error_handler_.GetBGError());
+    if (enough_room) {
+      *sfm_reserved_compact_space = true;
+    }
+  }
+#else
+  (void)cfd;
+  (void)inputs;
+  (void)sfm_reserved_compact_space;
+#endif  // ROCKSDB_LITE
+  if (!enough_room) {
+    // Just in case tests want to change the value of enough_room
+    TEST_SYNC_POINT_CALLBACK(
+        "DBImpl::BackgroundCompaction():CancelledCompaction", &enough_room);
+    ROCKS_LOG_BUFFER(log_buffer,
+                     "Cancelled compaction because not enough room");
+    RecordTick(stats_, COMPACTION_CANCELLED, 1);
+  }
+  return enough_room;
+}
+
+bool DBImpl::RequestCompactionToken(ColumnFamilyData* cfd, bool force,
+                                    std::unique_ptr<TaskLimiterToken>* token,
+                                    LogBuffer* log_buffer) {
+  assert(*token == nullptr);
+  auto limiter = static_cast<ConcurrentTaskLimiterImpl*>(
+      cfd->ioptions()->compaction_thread_limiter.get());
+  if (limiter == nullptr) {
+    return true;
+  }
+  *token = limiter->GetToken(force);
+  if (*token != nullptr) {
+    ROCKS_LOG_BUFFER(log_buffer,
+                     "Thread limiter [%s] increase [%s] compaction task, "
+                     "force: %s, tasks after: %d",
+                     limiter->GetName().c_str(), cfd->GetName().c_str(),
+                     force ? "true" : "false", limiter->GetOutstandingTask());
+    return true;
+  }
+  return false;
+}
+
+Status DBImpl::SyncClosedLogs(JobContext* job_context) {
+  TEST_SYNC_POINT("DBImpl::SyncClosedLogs:Start");
+  mutex_.AssertHeld();
+  autovector<log::Writer*, 1> logs_to_sync;
+  uint64_t current_log_number = logfile_number_;
+  while (logs_.front().number < current_log_number &&
+         logs_.front().getting_synced) {
+    log_sync_cv_.Wait();
+  }
+  for (auto it = logs_.begin();
+       it != logs_.end() && it->number < current_log_number; ++it) {
+    auto& log = *it;
+    assert(!log.getting_synced);
+    log.getting_synced = true;
+    logs_to_sync.push_back(log.writer);
+  }
+
+  Status s;
+  if (!logs_to_sync.empty()) {
+    mutex_.Unlock();
+
+    for (log::Writer* log : logs_to_sync) {
+      ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                     "[JOB %d] Syncing log #%" PRIu64, job_context->job_id,
+                     log->get_log_number());
+      s = log->file()->Sync(immutable_db_options_.use_fsync);
+      if (!s.ok()) {
+        break;
+      }
+    }
+    if (s.ok()) {
+      s = directories_.GetWalDir()->Fsync();
+    }
+
+    mutex_.Lock();
+
+    // "number <= current_log_number - 1" is equivalent to
+    // "number < current_log_number".
+    MarkLogsSynced(current_log_number - 1, true, s);
+    if (!s.ok()) {
+      error_handler_.SetBGError(s, BackgroundErrorReason::kFlush);
+      TEST_SYNC_POINT("DBImpl::SyncClosedLogs:Failed");
+      return s;
+    }
+  }
+  return s;
+}
+
+Status DBImpl::FlushMemTableToOutputFile(
+    ColumnFamilyData* cfd, const MutableCFOptions& mutable_cf_options,
+    bool* made_progress, JobContext* job_context,
+    SuperVersionContext* superversion_context,
+    std::vector<SequenceNumber>& snapshot_seqs,
+    SequenceNumber earliest_write_conflict_snapshot,
+    SnapshotChecker* snapshot_checker, LogBuffer* log_buffer,
+    Env::Priority thread_pri) {
+  mutex_.AssertHeld();
+  assert(cfd->imm()->NumNotFlushed() != 0);
+  assert(cfd->imm()->IsFlushPending());
+
+  FlushJob flush_job(
+      dbname_, cfd, immutable_db_options_, mutable_cf_options,
+      nullptr /* memtable_id */, env_options_for_compaction_, versions_.get(),
+      &mutex_, &shutting_down_, snapshot_seqs, earliest_write_conflict_snapshot,
+      snapshot_checker, job_context, log_buffer, directories_.GetDbDir(),
+      GetDataDir(cfd, 0U),
+      GetCompressionFlush(*cfd->ioptions(), mutable_cf_options), stats_,
+      &event_logger_, mutable_cf_options.report_bg_io_stats,
+      true /* sync_output_directory */, true /* write_manifest */, thread_pri);
+
+  FileMetaData file_meta;
+
+  TEST_SYNC_POINT("DBImpl::FlushMemTableToOutputFile:BeforePickMemtables");
+  flush_job.PickMemTable();
+  TEST_SYNC_POINT("DBImpl::FlushMemTableToOutputFile:AfterPickMemtables");
+
+#ifndef ROCKSDB_LITE
+  // may temporarily unlock and lock the mutex.
+  NotifyOnFlushBegin(cfd, &file_meta, mutable_cf_options, job_context->job_id,
+                     flush_job.GetTableProperties());
+#endif  // ROCKSDB_LITE
+
+  Status s;
+  if (logfile_number_ > 0 &&
+      versions_->GetColumnFamilySet()->NumberOfColumnFamilies() > 1) {
+    // If there are more than one column families, we need to make sure that
+    // all the log files except the most recent one are synced. Otherwise if
+    // the host crashes after flushing and before WAL is persistent, the
+    // flushed SST may contain data from write batches whose updates to
+    // other column families are missing.
+    // SyncClosedLogs() may unlock and re-lock the db_mutex.
+    s = SyncClosedLogs(job_context);
+  } else {
+    TEST_SYNC_POINT("DBImpl::SyncClosedLogs:Skip");
+  }
+
+  // Within flush_job.Run, rocksdb may call event listener to notify
+  // file creation and deletion.
+  //
+  // Note that flush_job.Run will unlock and lock the db_mutex,
+  // and EventListener callback will be called when the db_mutex
+  // is unlocked by the current thread.
+  if (s.ok()) {
+    s = flush_job.Run(&logs_with_prep_tracker_, &file_meta);
+  } else {
+    flush_job.Cancel();
+  }
+
+  if (s.ok()) {
+    InstallSuperVersionAndScheduleWork(cfd, superversion_context,
+                                       mutable_cf_options);
+    if (made_progress) {
+      *made_progress = true;
+    }
+    VersionStorageInfo::LevelSummaryStorage tmp;
+    ROCKS_LOG_BUFFER(log_buffer, "[%s] Level summary: %s\n",
+                     cfd->GetName().c_str(),
+                     cfd->current()->storage_info()->LevelSummary(&tmp));
+  }
+
+  if (!s.ok() && !s.IsShutdownInProgress()) {
+    Status new_bg_error = s;
+    error_handler_.SetBGError(new_bg_error, BackgroundErrorReason::kFlush);
+  }
+  if (s.ok()) {
+#ifndef ROCKSDB_LITE
+    // may temporarily unlock and lock the mutex.
+    NotifyOnFlushCompleted(cfd, &file_meta, mutable_cf_options,
+                           job_context->job_id, flush_job.GetTableProperties());
+    auto sfm = static_cast<SstFileManagerImpl*>(
+        immutable_db_options_.sst_file_manager.get());
+    if (sfm) {
+      // Notify sst_file_manager that a new file was added
+      std::string file_path = MakeTableFileName(
+          cfd->ioptions()->cf_paths[0].path, file_meta.fd.GetNumber());
+      sfm->OnAddFile(file_path);
+      if (sfm->IsMaxAllowedSpaceReached()) {
+        Status new_bg_error =
+            Status::SpaceLimit("Max allowed space was reached");
+        TEST_SYNC_POINT_CALLBACK(
+            "DBImpl::FlushMemTableToOutputFile:MaxAllowedSpaceReached",
+            &new_bg_error);
+        error_handler_.SetBGError(new_bg_error, BackgroundErrorReason::kFlush);
+      }
+    }
+#endif  // ROCKSDB_LITE
+  }
+  return s;
+}
+
+Status DBImpl::FlushMemTablesToOutputFiles(
+    const autovector<BGFlushArg>& bg_flush_args, bool* made_progress,
+    JobContext* job_context, LogBuffer* log_buffer, Env::Priority thread_pri) {
+  if (immutable_db_options_.atomic_flush) {
+    return AtomicFlushMemTablesToOutputFiles(
+        bg_flush_args, made_progress, job_context, log_buffer, thread_pri);
+  }
+  std::vector<SequenceNumber> snapshot_seqs;
+  SequenceNumber earliest_write_conflict_snapshot;
+  SnapshotChecker* snapshot_checker;
+  GetSnapshotContext(job_context, &snapshot_seqs,
+                     &earliest_write_conflict_snapshot, &snapshot_checker);
+  Status status;
+  for (auto& arg : bg_flush_args) {
+    ColumnFamilyData* cfd = arg.cfd_;
+    MutableCFOptions mutable_cf_options = *cfd->GetLatestMutableCFOptions();
+    SuperVersionContext* superversion_context = arg.superversion_context_;
+    Status s = FlushMemTableToOutputFile(
+        cfd, mutable_cf_options, made_progress, job_context,
+        superversion_context, snapshot_seqs, earliest_write_conflict_snapshot,
+        snapshot_checker, log_buffer, thread_pri);
+    if (!s.ok()) {
+      status = s;
+      if (!s.IsShutdownInProgress()) {
+        // At this point, DB is not shutting down, nor is cfd dropped.
+        // Something is wrong, thus we break out of the loop.
+        break;
+      }
+    }
+  }
+  return status;
+}
+
+/*
+ * Atomically flushes multiple column families.
+ *
+ * For each column family, all memtables with ID smaller than or equal to the
+ * ID specified in bg_flush_args will be flushed. Only after all column
+ * families finish flush will this function commit to MANIFEST. If any of the
+ * column families are not flushed successfully, this function does not have
+ * any side-effect on the state of the database.
+ */
+Status DBImpl::AtomicFlushMemTablesToOutputFiles(
+    const autovector<BGFlushArg>& bg_flush_args, bool* made_progress,
+    JobContext* job_context, LogBuffer* log_buffer, Env::Priority thread_pri) {
+  mutex_.AssertHeld();
+
+  autovector<ColumnFamilyData*> cfds;
+  for (const auto& arg : bg_flush_args) {
+    cfds.emplace_back(arg.cfd_);
+  }
+
+#ifndef NDEBUG
+  for (const auto cfd : cfds) {
+    assert(cfd->imm()->NumNotFlushed() != 0);
+    assert(cfd->imm()->IsFlushPending());
+  }
+#endif /* !NDEBUG */
+
+  std::vector<SequenceNumber> snapshot_seqs;
+  SequenceNumber earliest_write_conflict_snapshot;
+  SnapshotChecker* snapshot_checker;
+  GetSnapshotContext(job_context, &snapshot_seqs,
+                     &earliest_write_conflict_snapshot, &snapshot_checker);
+
+  autovector<Directory*> distinct_output_dirs;
+  autovector<std::string> distinct_output_dir_paths;
+  std::vector<FlushJob> jobs;
+  std::vector<MutableCFOptions> all_mutable_cf_options;
+  int num_cfs = static_cast<int>(cfds.size());
+  all_mutable_cf_options.reserve(num_cfs);
+  for (int i = 0; i < num_cfs; ++i) {
+    auto cfd = cfds[i];
+    Directory* data_dir = GetDataDir(cfd, 0U);
+    const std::string& curr_path = cfd->ioptions()->cf_paths[0].path;
+
+    // Add to distinct output directories if eligible. Use linear search. Since
+    // the number of elements in the vector is not large, performance should be
+    // tolerable.
+    bool found = false;
+    for (const auto& path : distinct_output_dir_paths) {
+      if (path == curr_path) {
+        found = true;
+        break;
+      }
+    }
+    if (!found) {
+      distinct_output_dir_paths.emplace_back(curr_path);
+      distinct_output_dirs.emplace_back(data_dir);
+    }
+
+    all_mutable_cf_options.emplace_back(*cfd->GetLatestMutableCFOptions());
+    const MutableCFOptions& mutable_cf_options = all_mutable_cf_options.back();
+    const uint64_t* max_memtable_id = &(bg_flush_args[i].max_memtable_id_);
+    jobs.emplace_back(
+        dbname_, cfd, immutable_db_options_, mutable_cf_options,
+        max_memtable_id, env_options_for_compaction_, versions_.get(), &mutex_,
+        &shutting_down_, snapshot_seqs, earliest_write_conflict_snapshot,
+        snapshot_checker, job_context, log_buffer, directories_.GetDbDir(),
+        data_dir, GetCompressionFlush(*cfd->ioptions(), mutable_cf_options),
+        stats_, &event_logger_, mutable_cf_options.report_bg_io_stats,
+        false /* sync_output_directory */, false /* write_manifest */,
+        thread_pri);
+    jobs.back().PickMemTable();
+  }
+
+  std::vector<FileMetaData> file_meta(num_cfs);
+  Status s;
+  assert(num_cfs == static_cast<int>(jobs.size()));
+
+#ifndef ROCKSDB_LITE
+  for (int i = 0; i != num_cfs; ++i) {
+    const MutableCFOptions& mutable_cf_options = all_mutable_cf_options.at(i);
+    // may temporarily unlock and lock the mutex.
+    NotifyOnFlushBegin(cfds[i], &file_meta[i], mutable_cf_options,
+                       job_context->job_id, jobs[i].GetTableProperties());
+  }
+#endif /* !ROCKSDB_LITE */
+
+  if (logfile_number_ > 0) {
+    // TODO (yanqin) investigate whether we should sync the closed logs for
+    // single column family case.
+    s = SyncClosedLogs(job_context);
+  }
+
+  // exec_status stores the execution status of flush_jobs as
+  // <bool /* executed */, Status /* status code */>
+  autovector<std::pair<bool, Status>> exec_status;
+  for (int i = 0; i != num_cfs; ++i) {
+    // Initially all jobs are not executed, with status OK.
+    exec_status.emplace_back(false, Status::OK());
+  }
+
+  if (s.ok()) {
+    // TODO (yanqin): parallelize jobs with threads.
+    for (int i = 1; i != num_cfs; ++i) {
+      exec_status[i].second =
+          jobs[i].Run(&logs_with_prep_tracker_, &file_meta[i]);
+      exec_status[i].first = true;
+    }
+    if (num_cfs > 1) {
+      TEST_SYNC_POINT(
+          "DBImpl::AtomicFlushMemTablesToOutputFiles:SomeFlushJobsComplete:1");
+      TEST_SYNC_POINT(
+          "DBImpl::AtomicFlushMemTablesToOutputFiles:SomeFlushJobsComplete:2");
+    }
+    exec_status[0].second =
+        jobs[0].Run(&logs_with_prep_tracker_, &file_meta[0]);
+    exec_status[0].first = true;
+
+    Status error_status;
+    for (const auto& e : exec_status) {
+      if (!e.second.ok()) {
+        s = e.second;
+        if (!e.second.IsShutdownInProgress()) {
+          // If a flush job did not return OK, and the CF is not dropped, and
+          // the DB is not shutting down, then we have to return this result to
+          // caller later.
+          error_status = e.second;
+        }
+      }
+    }
+
+    s = error_status.ok() ? s : error_status;
+  }
+
+  if (s.ok() || s.IsShutdownInProgress()) {
+    // Sync on all distinct output directories.
+    for (auto dir : distinct_output_dirs) {
+      if (dir != nullptr) {
+        s = dir->Fsync();
+        if (!s.ok()) {
+          break;
+        }
+      }
+    }
+  }
+
+  if (s.ok()) {
+    auto wait_to_install_func = [&]() {
+      bool ready = true;
+      for (size_t i = 0; i != cfds.size(); ++i) {
+        const auto& mems = jobs[i].GetMemTables();
+        if (cfds[i]->IsDropped()) {
+          // If the column family is dropped, then do not wait.
+          continue;
+        } else if (!mems.empty() &&
+                   cfds[i]->imm()->GetEarliestMemTableID() < mems[0]->GetID()) {
+          // If a flush job needs to install the flush result for mems and
+          // mems[0] is not the earliest memtable, it means another thread must
+          // be installing flush results for the same column family, then the
+          // current thread needs to wait.
+          ready = false;
+          break;
+        } else if (mems.empty() && cfds[i]->imm()->GetEarliestMemTableID() <=
+                                       bg_flush_args[i].max_memtable_id_) {
+          // If a flush job does not need to install flush results, then it has
+          // to wait until all memtables up to max_memtable_id_ (inclusive) are
+          // installed.
+          ready = false;
+          break;
+        }
+      }
+      return ready;
+    };
+
+    bool resuming_from_bg_err = error_handler_.IsDBStopped();
+    while ((!error_handler_.IsDBStopped() ||
+            error_handler_.GetRecoveryError().ok()) &&
+           !wait_to_install_func()) {
+      atomic_flush_install_cv_.Wait();
+    }
+
+    s = resuming_from_bg_err ? error_handler_.GetRecoveryError()
+                             : error_handler_.GetBGError();
+  }
+
+  if (s.ok()) {
+    autovector<ColumnFamilyData*> tmp_cfds;
+    autovector<const autovector<MemTable*>*> mems_list;
+    autovector<const MutableCFOptions*> mutable_cf_options_list;
+    autovector<FileMetaData*> tmp_file_meta;
+    for (int i = 0; i != num_cfs; ++i) {
+      const auto& mems = jobs[i].GetMemTables();
+      if (!cfds[i]->IsDropped() && !mems.empty()) {
+        tmp_cfds.emplace_back(cfds[i]);
+        mems_list.emplace_back(&mems);
+        mutable_cf_options_list.emplace_back(&all_mutable_cf_options[i]);
+        tmp_file_meta.emplace_back(&file_meta[i]);
+      }
+    }
+
+    s = InstallMemtableAtomicFlushResults(
+        nullptr /* imm_lists */, tmp_cfds, mutable_cf_options_list, mems_list,
+        versions_.get(), &mutex_, tmp_file_meta,
+        &job_context->memtables_to_free, directories_.GetDbDir(), log_buffer);
+  }
+
+  if (s.ok() || s.IsShutdownInProgress()) {
+    assert(num_cfs ==
+           static_cast<int>(job_context->superversion_contexts.size()));
+    for (int i = 0; i != num_cfs; ++i) {
+      if (cfds[i]->IsDropped()) {
+        continue;
+      }
+      InstallSuperVersionAndScheduleWork(cfds[i],
+                                         &job_context->superversion_contexts[i],
+                                         all_mutable_cf_options[i]);
+      VersionStorageInfo::LevelSummaryStorage tmp;
+      ROCKS_LOG_BUFFER(log_buffer, "[%s] Level summary: %s\n",
+                       cfds[i]->GetName().c_str(),
+                       cfds[i]->current()->storage_info()->LevelSummary(&tmp));
+    }
+    if (made_progress) {
+      *made_progress = true;
+    }
+#ifndef ROCKSDB_LITE
+    auto sfm = static_cast<SstFileManagerImpl*>(
+        immutable_db_options_.sst_file_manager.get());
+    for (int i = 0; i != num_cfs; ++i) {
+      if (cfds[i]->IsDropped()) {
+        continue;
+      }
+      NotifyOnFlushCompleted(cfds[i], &file_meta[i], all_mutable_cf_options[i],
+                             job_context->job_id, jobs[i].GetTableProperties());
+      if (sfm) {
+        std::string file_path = MakeTableFileName(
+            cfds[i]->ioptions()->cf_paths[0].path, file_meta[i].fd.GetNumber());
+        sfm->OnAddFile(file_path);
+        if (sfm->IsMaxAllowedSpaceReached() &&
+            error_handler_.GetBGError().ok()) {
+          Status new_bg_error =
+              Status::SpaceLimit("Max allowed space was reached");
+          error_handler_.SetBGError(new_bg_error,
+                                    BackgroundErrorReason::kFlush);
+        }
+      }
+    }
+#endif  // ROCKSDB_LITE
+  }
+
+  // Need to undo atomic flush if something went wrong, i.e. s is not OK and
+  // it is not because of CF drop.
+  if (!s.ok() && !s.IsShutdownInProgress()) {
+    // Have to cancel the flush jobs that have NOT executed because we need to
+    // unref the versions.
+    for (int i = 0; i != num_cfs; ++i) {
+      if (!exec_status[i].first) {
+        jobs[i].Cancel();
+      }
+    }
+    for (int i = 0; i != num_cfs; ++i) {
+      if (exec_status[i].first && exec_status[i].second.ok()) {
+        auto& mems = jobs[i].GetMemTables();
+        cfds[i]->imm()->RollbackMemtableFlush(mems,
+                                              file_meta[i].fd.GetNumber());
+      }
+    }
+    Status new_bg_error = s;
+    error_handler_.SetBGError(new_bg_error, BackgroundErrorReason::kFlush);
+  }
+
+  return s;
+}
+
+void DBImpl::NotifyOnFlushBegin(ColumnFamilyData* cfd, FileMetaData* file_meta,
+                                const MutableCFOptions& mutable_cf_options,
+                                int job_id, TableProperties prop) {
+#ifndef ROCKSDB_LITE
+  if (immutable_db_options_.listeners.size() == 0U) {
+    return;
+  }
+  mutex_.AssertHeld();
+  if (shutting_down_.load(std::memory_order_acquire)) {
+    return;
+  }
+  bool triggered_writes_slowdown =
+      (cfd->current()->storage_info()->NumLevelFiles(0) >=
+       mutable_cf_options.level0_slowdown_writes_trigger);
+  bool triggered_writes_stop =
+      (cfd->current()->storage_info()->NumLevelFiles(0) >=
+       mutable_cf_options.level0_stop_writes_trigger);
+  // release lock while notifying events
+  mutex_.Unlock();
+  {
+    FlushJobInfo info;
+    info.cf_id = cfd->GetID();
+    info.cf_name = cfd->GetName();
+    // TODO(yhchiang): make db_paths dynamic in case flush does not
+    //                 go to L0 in the future.
+    info.file_path = MakeTableFileName(cfd->ioptions()->cf_paths[0].path,
+                                       file_meta->fd.GetNumber());
+    info.thread_id = env_->GetThreadID();
+    info.job_id = job_id;
+    info.triggered_writes_slowdown = triggered_writes_slowdown;
+    info.triggered_writes_stop = triggered_writes_stop;
+    info.smallest_seqno = file_meta->fd.smallest_seqno;
+    info.largest_seqno = file_meta->fd.largest_seqno;
+    info.table_properties = prop;
+    info.flush_reason = cfd->GetFlushReason();
+    for (auto listener : immutable_db_options_.listeners) {
+      listener->OnFlushBegin(this, info);
+    }
+  }
+  mutex_.Lock();
+// no need to signal bg_cv_ as it will be signaled at the end of the
+// flush process.
+#else
+  (void)cfd;
+  (void)file_meta;
+  (void)mutable_cf_options;
+  (void)job_id;
+  (void)prop;
+#endif  // ROCKSDB_LITE
+}
+
+void DBImpl::NotifyOnFlushCompleted(ColumnFamilyData* cfd,
+                                    FileMetaData* file_meta,
+                                    const MutableCFOptions& mutable_cf_options,
+                                    int job_id, TableProperties prop) {
+#ifndef ROCKSDB_LITE
+  if (immutable_db_options_.listeners.size() == 0U) {
+    return;
+  }
+  mutex_.AssertHeld();
+  if (shutting_down_.load(std::memory_order_acquire)) {
+    return;
+  }
+  bool triggered_writes_slowdown =
+      (cfd->current()->storage_info()->NumLevelFiles(0) >=
+       mutable_cf_options.level0_slowdown_writes_trigger);
+  bool triggered_writes_stop =
+      (cfd->current()->storage_info()->NumLevelFiles(0) >=
+       mutable_cf_options.level0_stop_writes_trigger);
+  // release lock while notifying events
+  mutex_.Unlock();
+  {
+    FlushJobInfo info;
+    info.cf_id = cfd->GetID();
+    info.cf_name = cfd->GetName();
+    // TODO(yhchiang): make db_paths dynamic in case flush does not
+    //                 go to L0 in the future.
+    info.file_path = MakeTableFileName(cfd->ioptions()->cf_paths[0].path,
+                                       file_meta->fd.GetNumber());
+    info.thread_id = env_->GetThreadID();
+    info.job_id = job_id;
+    info.triggered_writes_slowdown = triggered_writes_slowdown;
+    info.triggered_writes_stop = triggered_writes_stop;
+    info.smallest_seqno = file_meta->fd.smallest_seqno;
+    info.largest_seqno = file_meta->fd.largest_seqno;
+    info.table_properties = prop;
+    info.flush_reason = cfd->GetFlushReason();
+    for (auto listener : immutable_db_options_.listeners) {
+      listener->OnFlushCompleted(this, info);
+    }
+  }
+  mutex_.Lock();
+  // no need to signal bg_cv_ as it will be signaled at the end of the
+  // flush process.
+#else
+  (void)cfd;
+  (void)file_meta;
+  (void)mutable_cf_options;
+  (void)job_id;
+  (void)prop;
+#endif  // ROCKSDB_LITE
+}
+
+Status DBImpl::CompactRange(const CompactRangeOptions& options,
+                            ColumnFamilyHandle* column_family,
+                            const Slice* begin, const Slice* end) {
+  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
+  auto cfd = cfh->cfd();
+
+  if (options.target_path_id >= cfd->ioptions()->cf_paths.size()) {
+    return Status::InvalidArgument("Invalid target path ID");
+  }
+
+  bool exclusive = options.exclusive_manual_compaction;
+
+  bool flush_needed = true;
+  if (begin != nullptr && end != nullptr) {
+    // TODO(ajkr): We could also optimize away the flush in certain cases where
+    // one/both sides of the interval are unbounded. But it requires more
+    // changes to RangesOverlapWithMemtables.
+    Range range(*begin, *end);
+    SuperVersion* super_version = cfd->GetReferencedSuperVersion(&mutex_);
+    cfd->RangesOverlapWithMemtables({range}, super_version, &flush_needed);
+    CleanupSuperVersion(super_version);
+  }
+
+  Status s;
+  if (flush_needed) {
+    FlushOptions fo;
+    fo.allow_write_stall = options.allow_write_stall;
+    if (immutable_db_options_.atomic_flush) {
+      autovector<ColumnFamilyData*> cfds;
+      mutex_.Lock();
+      SelectColumnFamiliesForAtomicFlush(&cfds);
+      mutex_.Unlock();
+      s = AtomicFlushMemTables(cfds, fo, FlushReason::kManualCompaction,
+                               false /* writes_stopped */);
+    } else {
+      s = FlushMemTable(cfd, fo, FlushReason::kManualCompaction,
+                        false /* writes_stopped*/);
+    }
+    if (!s.ok()) {
+      LogFlush(immutable_db_options_.info_log);
+      return s;
+    }
+  }
+
+  int max_level_with_files = 0;
+  {
+    InstrumentedMutexLock l(&mutex_);
+    Version* base = cfd->current();
+    for (int level = 1; level < base->storage_info()->num_non_empty_levels();
+         level++) {
+      if (base->storage_info()->OverlapInLevel(level, begin, end)) {
+        max_level_with_files = level;
+      }
+    }
+  }
+
+  int final_output_level = 0;
+  if (cfd->ioptions()->compaction_style == kCompactionStyleUniversal &&
+      cfd->NumberLevels() > 1) {
+    // Always compact all files together.
+    final_output_level = cfd->NumberLevels() - 1;
+    // if bottom most level is reserved
+    if (immutable_db_options_.allow_ingest_behind) {
+      final_output_level--;
+    }
+    s = RunManualCompaction(cfd, ColumnFamilyData::kCompactAllLevels,
+                            final_output_level, options.target_path_id,
+                            options.max_subcompactions, begin, end, exclusive);
+  } else {
+    for (int level = 0; level <= max_level_with_files; level++) {
+      int output_level;
+      // in case the compaction is universal or if we're compacting the
+      // bottom-most level, the output level will be the same as input one.
+      // level 0 can never be the bottommost level (i.e. if all files are in
+      // level 0, we will compact to level 1)
+      if (cfd->ioptions()->compaction_style == kCompactionStyleUniversal ||
+          cfd->ioptions()->compaction_style == kCompactionStyleFIFO) {
+        output_level = level;
+      } else if (level == max_level_with_files && level > 0) {
+        if (options.bottommost_level_compaction ==
+            BottommostLevelCompaction::kSkip) {
+          // Skip bottommost level compaction
+          continue;
+        } else if (options.bottommost_level_compaction ==
+                       BottommostLevelCompaction::kIfHaveCompactionFilter &&
+                   cfd->ioptions()->compaction_filter == nullptr &&
+                   cfd->ioptions()->compaction_filter_factory == nullptr) {
+          // Skip bottommost level compaction since we don't have a compaction
+          // filter
+          continue;
+        }
+        output_level = level;
+      } else {
+        output_level = level + 1;
+        if (cfd->ioptions()->compaction_style == kCompactionStyleLevel &&
+            cfd->ioptions()->level_compaction_dynamic_level_bytes &&
+            level == 0) {
+          output_level = ColumnFamilyData::kCompactToBaseLevel;
+        }
+      }
+      s = RunManualCompaction(cfd, level, output_level, options.target_path_id,
+                              options.max_subcompactions, begin, end,
+                              exclusive);
+      if (!s.ok()) {
+        break;
+      }
+      if (output_level == ColumnFamilyData::kCompactToBaseLevel) {
+        final_output_level = cfd->NumberLevels() - 1;
+      } else if (output_level > final_output_level) {
+        final_output_level = output_level;
+      }
+      TEST_SYNC_POINT("DBImpl::RunManualCompaction()::1");
+      TEST_SYNC_POINT("DBImpl::RunManualCompaction()::2");
+    }
+  }
+  if (!s.ok()) {
+    LogFlush(immutable_db_options_.info_log);
+    return s;
+  }
+
+  if (options.change_level) {
+    ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                   "[RefitLevel] waiting for background threads to stop");
+    s = PauseBackgroundWork();
+    if (s.ok()) {
+      s = ReFitLevel(cfd, final_output_level, options.target_level);
+    }
+    ContinueBackgroundWork();
+  }
+  LogFlush(immutable_db_options_.info_log);
+
+  {
+    InstrumentedMutexLock l(&mutex_);
+    // an automatic compaction that has been scheduled might have been
+    // preempted by the manual compactions. Need to schedule it back.
+    MaybeScheduleFlushOrCompaction();
+  }
+
+  return s;
+}
+
+Status DBImpl::CompactFiles(const CompactionOptions& compact_options,
+                            ColumnFamilyHandle* column_family,
+                            const std::vector<std::string>& input_file_names,
+                            const int output_level, const int output_path_id,
+                            std::vector<std::string>* const output_file_names,
+                            CompactionJobInfo* compaction_job_info) {
+#ifdef ROCKSDB_LITE
+  (void)compact_options;
+  (void)column_family;
+  (void)input_file_names;
+  (void)output_level;
+  (void)output_path_id;
+  (void)output_file_names;
+  (void)compaction_job_info;
+  // not supported in lite version
+  return Status::NotSupported("Not supported in ROCKSDB LITE");
+#else
+  if (column_family == nullptr) {
+    return Status::InvalidArgument("ColumnFamilyHandle must be non-null.");
+  }
+
+  auto cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
+  assert(cfd);
+
+  Status s;
+  JobContext job_context(0, true);
+  LogBuffer log_buffer(InfoLogLevel::INFO_LEVEL,
+                       immutable_db_options_.info_log.get());
+
+  // Perform CompactFiles
+  TEST_SYNC_POINT("TestCompactFiles::IngestExternalFile2");
+  {
+    InstrumentedMutexLock l(&mutex_);
+
+    // This call will unlock/lock the mutex to wait for current running
+    // IngestExternalFile() calls to finish.
+    WaitForIngestFile();
+
+    // We need to get current after `WaitForIngestFile`, because
+    // `IngestExternalFile` may add files that overlap with `input_file_names`
+    auto* current = cfd->current();
+    current->Ref();
+
+    s = CompactFilesImpl(compact_options, cfd, current, input_file_names,
+                         output_file_names, output_level, output_path_id,
+                         &job_context, &log_buffer, compaction_job_info);
+
+    current->Unref();
+  }
+
+  // Find and delete obsolete files
+  {
+    InstrumentedMutexLock l(&mutex_);
+    // 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
+    // catch all created files if compaction failed.
+    FindObsoleteFiles(&job_context, !s.ok());
+  }  // release the mutex
+
+  // delete unnecessary files if any, this is done outside the mutex
+  if (job_context.HaveSomethingToClean() ||
+      job_context.HaveSomethingToDelete() || !log_buffer.IsEmpty()) {
+    // Have to flush the info logs before bg_compaction_scheduled_--
+    // because if bg_flush_scheduled_ becomes 0 and the lock is
+    // released, the deconstructor of DB can kick in and destroy all the
+    // states of DB so info_log might not be available after that point.
+    // It also applies to access other states that DB owns.
+    log_buffer.FlushBufferToLog();
+    if (job_context.HaveSomethingToDelete()) {
+      // no mutex is locked here.  No need to Unlock() and Lock() here.
+      PurgeObsoleteFiles(job_context);
+    }
+    job_context.Clean();
+  }
+
+  return s;
+#endif  // ROCKSDB_LITE
+}
+
+#ifndef ROCKSDB_LITE
+Status DBImpl::CompactFilesImpl(
+    const CompactionOptions& compact_options, ColumnFamilyData* cfd,
+    Version* version, const std::vector<std::string>& input_file_names,
+    std::vector<std::string>* const output_file_names, const int output_level,
+    int output_path_id, JobContext* job_context, LogBuffer* log_buffer,
+    CompactionJobInfo* compaction_job_info) {
+  mutex_.AssertHeld();
+
+  if (shutting_down_.load(std::memory_order_acquire)) {
+    return Status::ShutdownInProgress();
+  }
+
+  std::unordered_set<uint64_t> input_set;
+  for (const auto& file_name : input_file_names) {
+    input_set.insert(TableFileNameToNumber(file_name));
+  }
+
+  ColumnFamilyMetaData cf_meta;
+  // TODO(yhchiang): can directly use version here if none of the
+  // following functions call is pluggable to external developers.
+  version->GetColumnFamilyMetaData(&cf_meta);
+
+  if (output_path_id < 0) {
+    if (cfd->ioptions()->cf_paths.size() == 1U) {
+      output_path_id = 0;
+    } else {
+      return Status::NotSupported(
+          "Automatic output path selection is not "
+          "yet supported in CompactFiles()");
+    }
+  }
+
+  Status s = cfd->compaction_picker()->SanitizeCompactionInputFiles(
+      &input_set, cf_meta, output_level);
+  if (!s.ok()) {
+    return s;
+  }
+
+  std::vector<CompactionInputFiles> input_files;
+  s = cfd->compaction_picker()->GetCompactionInputsFromFileNumbers(
+      &input_files, &input_set, version->storage_info(), compact_options);
+  if (!s.ok()) {
+    return s;
+  }
+
+  for (const auto& inputs : input_files) {
+    if (cfd->compaction_picker()->AreFilesInCompaction(inputs.files)) {
+      return Status::Aborted(
+          "Some of the necessary compaction input "
+          "files are already being compacted");
+    }
+  }
+  bool sfm_reserved_compact_space = false;
+  // First check if we have enough room to do the compaction
+  bool enough_room = EnoughRoomForCompaction(
+      cfd, input_files, &sfm_reserved_compact_space, log_buffer);
+
+  if (!enough_room) {
+    // m's vars will get set properly at the end of this function,
+    // as long as status == CompactionTooLarge
+    return Status::CompactionTooLarge();
+  }
+
+  // At this point, CompactFiles will be run.
+  bg_compaction_scheduled_++;
+
+  std::unique_ptr<Compaction> c;
+  assert(cfd->compaction_picker());
+  c.reset(cfd->compaction_picker()->CompactFiles(
+      compact_options, input_files, output_level, version->storage_info(),
+      *cfd->GetLatestMutableCFOptions(), output_path_id));
+  // we already sanitized the set of input files and checked for conflicts
+  // without releasing the lock, so we're guaranteed a compaction can be formed.
+  assert(c != nullptr);
+
+  c->SetInputVersion(version);
+  // deletion compaction currently not allowed in CompactFiles.
+  assert(!c->deletion_compaction());
+
+  std::vector<SequenceNumber> snapshot_seqs;
+  SequenceNumber earliest_write_conflict_snapshot;
+  SnapshotChecker* snapshot_checker;
+  GetSnapshotContext(job_context, &snapshot_seqs,
+                     &earliest_write_conflict_snapshot, &snapshot_checker);
+
+  auto pending_outputs_inserted_elem =
+      CaptureCurrentFileNumberInPendingOutputs();
+
+  assert(is_snapshot_supported_ || snapshots_.empty());
+  CompactionJobStats compaction_job_stats;
+  CompactionJob compaction_job(
+      job_context->job_id, c.get(), immutable_db_options_,
+      env_options_for_compaction_, versions_.get(), &shutting_down_,
+      preserve_deletes_seqnum_.load(), log_buffer, directories_.GetDbDir(),
+      GetDataDir(c->column_family_data(), c->output_path_id()), stats_, &mutex_,
+      &error_handler_, snapshot_seqs, earliest_write_conflict_snapshot,
+      snapshot_checker, table_cache_, &event_logger_,
+      c->mutable_cf_options()->paranoid_file_checks,
+      c->mutable_cf_options()->report_bg_io_stats, dbname_,
+      &compaction_job_stats, Env::Priority::USER);
+
+  // Creating a compaction influences the compaction score because the score
+  // takes running compactions into account (by skipping files that are already
+  // being compacted). Since we just changed compaction score, we recalculate it
+  // here.
+  version->storage_info()->ComputeCompactionScore(*cfd->ioptions(),
+                                                  *c->mutable_cf_options());
+
+  compaction_job.Prepare();
+
+  mutex_.Unlock();
+  TEST_SYNC_POINT("CompactFilesImpl:0");
+  TEST_SYNC_POINT("CompactFilesImpl:1");
+  compaction_job.Run();
+  TEST_SYNC_POINT("CompactFilesImpl:2");
+  TEST_SYNC_POINT("CompactFilesImpl:3");
+  mutex_.Lock();
+
+  Status status = compaction_job.Install(*c->mutable_cf_options());
+  if (status.ok()) {
+    InstallSuperVersionAndScheduleWork(c->column_family_data(),
+                                       &job_context->superversion_contexts[0],
+                                       *c->mutable_cf_options());
+  }
+  c->ReleaseCompactionFiles(s);
+#ifndef ROCKSDB_LITE
+  // Need to make sure SstFileManager does its bookkeeping
+  auto sfm = static_cast<SstFileManagerImpl*>(
+      immutable_db_options_.sst_file_manager.get());
+  if (sfm && sfm_reserved_compact_space) {
+    sfm->OnCompactionCompletion(c.get());
+  }
+#endif  // ROCKSDB_LITE
+
+  ReleaseFileNumberFromPendingOutputs(pending_outputs_inserted_elem);
+
+  if (compaction_job_info != nullptr) {
+    BuildCompactionJobInfo(cfd, c.get(), s, compaction_job_stats,
+                           job_context->job_id, version, compaction_job_info);
+  }
+
+  if (status.ok()) {
+    // Done
+  } else if (status.IsShutdownInProgress()) {
+    // Ignore compaction errors found during shutting down
+  } else {
+    ROCKS_LOG_WARN(immutable_db_options_.info_log,
+                   "[%s] [JOB %d] Compaction error: %s",
+                   c->column_family_data()->GetName().c_str(),
+                   job_context->job_id, status.ToString().c_str());
+    error_handler_.SetBGError(status, BackgroundErrorReason::kCompaction);
+  }
+
+  if (output_file_names != nullptr) {
+    for (const auto newf : c->edit()->GetNewFiles()) {
+      (*output_file_names)
+          .push_back(TableFileName(c->immutable_cf_options()->cf_paths,
+                                   newf.second.fd.GetNumber(),
+                                   newf.second.fd.GetPathId()));
+    }
+  }
+
+  c.reset();
+
+  bg_compaction_scheduled_--;
+  if (bg_compaction_scheduled_ == 0) {
+    bg_cv_.SignalAll();
+  }
+  MaybeScheduleFlushOrCompaction();
+  TEST_SYNC_POINT("CompactFilesImpl:End");
+
+  return status;
+}
+#endif  // ROCKSDB_LITE
+
+Status DBImpl::PauseBackgroundWork() {
+  InstrumentedMutexLock guard_lock(&mutex_);
+  bg_compaction_paused_++;
+  while (bg_bottom_compaction_scheduled_ > 0 || bg_compaction_scheduled_ > 0 ||
+         bg_flush_scheduled_ > 0) {
+    bg_cv_.Wait();
+  }
+  bg_work_paused_++;
+  return Status::OK();
+}
+
+Status DBImpl::ContinueBackgroundWork() {
+  InstrumentedMutexLock guard_lock(&mutex_);
+  if (bg_work_paused_ == 0) {
+    return Status::InvalidArgument();
+  }
+  assert(bg_work_paused_ > 0);
+  assert(bg_compaction_paused_ > 0);
+  bg_compaction_paused_--;
+  bg_work_paused_--;
+  // It's sufficient to check just bg_work_paused_ here since
+  // bg_work_paused_ is always no greater than bg_compaction_paused_
+  if (bg_work_paused_ == 0) {
+    MaybeScheduleFlushOrCompaction();
+  }
+  return Status::OK();
+}
+
+void DBImpl::NotifyOnCompactionBegin(ColumnFamilyData* cfd, Compaction* c,
+                                     const Status& st,
+                                     const CompactionJobStats& job_stats,
+                                     int job_id) {
+#ifndef ROCKSDB_LITE
+  if (immutable_db_options_.listeners.empty()) {
+    return;
+  }
+  mutex_.AssertHeld();
+  if (shutting_down_.load(std::memory_order_acquire)) {
+    return;
+  }
+  Version* current = cfd->current();
+  current->Ref();
+  // release lock while notifying events
+  mutex_.Unlock();
+  TEST_SYNC_POINT("DBImpl::NotifyOnCompactionBegin::UnlockMutex");
+  {
+    CompactionJobInfo info;
+    info.cf_name = cfd->GetName();
+    info.status = st;
+    info.thread_id = env_->GetThreadID();
+    info.job_id = job_id;
+    info.base_input_level = c->start_level();
+    info.output_level = c->output_level();
+    info.stats = job_stats;
+    info.table_properties = c->GetOutputTableProperties();
+    info.compaction_reason = c->compaction_reason();
+    info.compression = c->output_compression();
+    for (size_t i = 0; i < c->num_input_levels(); ++i) {
+      for (const auto fmd : *c->inputs(i)) {
+        auto fn = TableFileName(c->immutable_cf_options()->cf_paths,
+                                fmd->fd.GetNumber(), fmd->fd.GetPathId());
+        info.input_files.push_back(fn);
+        if (info.table_properties.count(fn) == 0) {
+          std::shared_ptr<const TableProperties> tp;
+          auto s = current->GetTableProperties(&tp, fmd, &fn);
+          if (s.ok()) {
+            info.table_properties[fn] = tp;
+          }
+        }
+      }
+    }
+    for (const auto newf : c->edit()->GetNewFiles()) {
+      info.output_files.push_back(TableFileName(
+          c->immutable_cf_options()->cf_paths, newf.second.fd.GetNumber(),
+          newf.second.fd.GetPathId()));
+    }
+    for (auto listener : immutable_db_options_.listeners) {
+      listener->OnCompactionBegin(this, info);
+    }
+  }
+  mutex_.Lock();
+  current->Unref();
+#else
+  (void)cfd;
+  (void)c;
+  (void)st;
+  (void)job_stats;
+  (void)job_id;
+#endif  // ROCKSDB_LITE
+}
+
+void DBImpl::NotifyOnCompactionCompleted(
+    ColumnFamilyData* cfd, Compaction* c, const Status& st,
+    const CompactionJobStats& compaction_job_stats, const int job_id) {
+#ifndef ROCKSDB_LITE
+  if (immutable_db_options_.listeners.size() == 0U) {
+    return;
+  }
+  mutex_.AssertHeld();
+  if (shutting_down_.load(std::memory_order_acquire)) {
+    return;
+  }
+  Version* current = cfd->current();
+  current->Ref();
+  // release lock while notifying events
+  mutex_.Unlock();
+  TEST_SYNC_POINT("DBImpl::NotifyOnCompactionCompleted::UnlockMutex");
+  {
+    CompactionJobInfo info;
+    BuildCompactionJobInfo(cfd, c, st, compaction_job_stats, job_id, current,
+                           &info);
+    for (auto listener : immutable_db_options_.listeners) {
+      listener->OnCompactionCompleted(this, info);
+    }
+  }
+  mutex_.Lock();
+  current->Unref();
+  // no need to signal bg_cv_ as it will be signaled at the end of the
+  // flush process.
+#else
+  (void)cfd;
+  (void)c;
+  (void)st;
+  (void)compaction_job_stats;
+  (void)job_id;
+#endif  // ROCKSDB_LITE
+}
+
+// REQUIREMENT: block all background work by calling PauseBackgroundWork()
+// before calling this function
+Status DBImpl::ReFitLevel(ColumnFamilyData* cfd, int level, int target_level) {
+  assert(level < cfd->NumberLevels());
+  if (target_level >= cfd->NumberLevels()) {
+    return Status::InvalidArgument("Target level exceeds number of levels");
+  }
+
+  SuperVersionContext sv_context(/* create_superversion */ true);
+
+  Status status;
+
+  InstrumentedMutexLock guard_lock(&mutex_);
+
+  // only allow one thread refitting
+  if (refitting_level_) {
+    ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                   "[ReFitLevel] another thread is refitting");
+    return Status::NotSupported("another thread is refitting");
+  }
+  refitting_level_ = true;
+
+  const MutableCFOptions mutable_cf_options = *cfd->GetLatestMutableCFOptions();
+  // move to a smaller level
+  int to_level = target_level;
+  if (target_level < 0) {
+    to_level = FindMinimumEmptyLevelFitting(cfd, mutable_cf_options, level);
+  }
+
+  auto* vstorage = cfd->current()->storage_info();
+  if (to_level > level) {
+    if (level == 0) {
+      return Status::NotSupported(
+          "Cannot change from level 0 to other levels.");
+    }
+    // Check levels are empty for a trivial move
+    for (int l = level + 1; l <= to_level; l++) {
+      if (vstorage->NumLevelFiles(l) > 0) {
+        return Status::NotSupported(
+            "Levels between source and target are not empty for a move.");
+      }
+    }
+  }
+  if (to_level != level) {
+    ROCKS_LOG_DEBUG(immutable_db_options_.info_log,
+                    "[%s] Before refitting:\n%s", cfd->GetName().c_str(),
+                    cfd->current()->DebugString().data());
+
+    VersionEdit edit;
+    edit.SetColumnFamily(cfd->GetID());
+    for (const auto& f : vstorage->LevelFiles(level)) {
+      edit.DeleteFile(level, f->fd.GetNumber());
+      edit.AddFile(to_level, f->fd.GetNumber(), f->fd.GetPathId(),
+                   f->fd.GetFileSize(), f->smallest, f->largest,
+                   f->fd.smallest_seqno, f->fd.largest_seqno,
+                   f->marked_for_compaction);
+    }
+    ROCKS_LOG_DEBUG(immutable_db_options_.info_log,
+                    "[%s] Apply version edit:\n%s", cfd->GetName().c_str(),
+                    edit.DebugString().data());
+
+    status = versions_->LogAndApply(cfd, mutable_cf_options, &edit, &mutex_,
+                                    directories_.GetDbDir());
+    InstallSuperVersionAndScheduleWork(cfd, &sv_context, mutable_cf_options);
+
+    ROCKS_LOG_DEBUG(immutable_db_options_.info_log, "[%s] LogAndApply: %s\n",
+                    cfd->GetName().c_str(), status.ToString().data());
+
+    if (status.ok()) {
+      ROCKS_LOG_DEBUG(immutable_db_options_.info_log,
+                      "[%s] After refitting:\n%s", cfd->GetName().c_str(),
+                      cfd->current()->DebugString().data());
+    }
+  }
+
+  sv_context.Clean();
+  refitting_level_ = false;
+
+  return status;
+}
+
+int DBImpl::NumberLevels(ColumnFamilyHandle* column_family) {
+  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
+  return cfh->cfd()->NumberLevels();
+}
+
+int DBImpl::MaxMemCompactionLevel(ColumnFamilyHandle* /*column_family*/) {
+  return 0;
+}
+
+int DBImpl::Level0StopWriteTrigger(ColumnFamilyHandle* column_family) {
+  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
+  InstrumentedMutexLock l(&mutex_);
+  return cfh->cfd()
+      ->GetSuperVersion()
+      ->mutable_cf_options.level0_stop_writes_trigger;
+}
+
+Status DBImpl::Flush(const FlushOptions& flush_options,
+                     ColumnFamilyHandle* column_family) {
+  auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
+  ROCKS_LOG_INFO(immutable_db_options_.info_log, "[%s] Manual flush start.",
+                 cfh->GetName().c_str());
+  Status s;
+  if (immutable_db_options_.atomic_flush) {
+    s = AtomicFlushMemTables({cfh->cfd()}, flush_options,
+                             FlushReason::kManualFlush);
+  } else {
+    s = FlushMemTable(cfh->cfd(), flush_options, FlushReason::kManualFlush);
+  }
+
+  ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                 "[%s] Manual flush finished, status: %s\n",
+                 cfh->GetName().c_str(), s.ToString().c_str());
+  return s;
+}
+
+Status DBImpl::Flush(const FlushOptions& flush_options,
+                     const std::vector<ColumnFamilyHandle*>& column_families) {
+  Status s;
+  if (!immutable_db_options_.atomic_flush) {
+    for (auto cfh : column_families) {
+      s = Flush(flush_options, cfh);
+      if (!s.ok()) {
+        break;
+      }
+    }
+  } else {
+    ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                   "Manual atomic flush start.\n"
+                   "=====Column families:=====");
+    for (auto cfh : column_families) {
+      auto cfhi = static_cast<ColumnFamilyHandleImpl*>(cfh);
+      ROCKS_LOG_INFO(immutable_db_options_.info_log, "%s",
+                     cfhi->GetName().c_str());
+    }
+    ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                   "=====End of column families list=====");
+    autovector<ColumnFamilyData*> cfds;
+    std::for_each(column_families.begin(), column_families.end(),
+                  [&cfds](ColumnFamilyHandle* elem) {
+                    auto cfh = static_cast<ColumnFamilyHandleImpl*>(elem);
+                    cfds.emplace_back(cfh->cfd());
+                  });
+    s = AtomicFlushMemTables(cfds, flush_options, FlushReason::kManualFlush);
+    ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                   "Manual atomic flush finished, status: %s\n"
+                   "=====Column families:=====",
+                   s.ToString().c_str());
+    for (auto cfh : column_families) {
+      auto cfhi = static_cast<ColumnFamilyHandleImpl*>(cfh);
+      ROCKS_LOG_INFO(immutable_db_options_.info_log, "%s",
+                     cfhi->GetName().c_str());
+    }
+    ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                   "=====End of column families list=====");
+  }
+  return s;
+}
+
+Status DBImpl::RunManualCompaction(ColumnFamilyData* cfd, int input_level,
+                                   int output_level, uint32_t output_path_id,
+                                   uint32_t max_subcompactions,
+                                   const Slice* begin, const Slice* end,
+                                   bool exclusive, bool disallow_trivial_move) {
+  assert(input_level == ColumnFamilyData::kCompactAllLevels ||
+         input_level >= 0);
+
+  InternalKey begin_storage, end_storage;
+  CompactionArg* ca;
+
+  bool scheduled = false;
+  bool manual_conflict = false;
+  ManualCompactionState manual;
+  manual.cfd = cfd;
+  manual.input_level = input_level;
+  manual.output_level = output_level;
+  manual.output_path_id = output_path_id;
+  manual.done = false;
+  manual.in_progress = false;
+  manual.incomplete = false;
+  manual.exclusive = exclusive;
+  manual.disallow_trivial_move = disallow_trivial_move;
+  // For universal compaction, we enforce every manual compaction to compact
+  // all files.
+  if (begin == nullptr ||
+      cfd->ioptions()->compaction_style == kCompactionStyleUniversal ||
+      cfd->ioptions()->compaction_style == kCompactionStyleFIFO) {
+    manual.begin = nullptr;
+  } else {
+    begin_storage.SetMinPossibleForUserKey(*begin);
+    manual.begin = &begin_storage;
+  }
+  if (end == nullptr ||
+      cfd->ioptions()->compaction_style == kCompactionStyleUniversal ||
+      cfd->ioptions()->compaction_style == kCompactionStyleFIFO) {
+    manual.end = nullptr;
+  } else {
+    end_storage.SetMaxPossibleForUserKey(*end);
+    manual.end = &end_storage;
+  }
+
+  TEST_SYNC_POINT("DBImpl::RunManualCompaction:0");
+  TEST_SYNC_POINT("DBImpl::RunManualCompaction:1");
+  InstrumentedMutexLock l(&mutex_);
+
+  // When a manual compaction arrives, temporarily disable scheduling of
+  // non-manual compactions and wait until the number of scheduled compaction
+  // jobs drops to zero. This is needed to ensure that this manual compaction
+  // can compact any range of keys/files.
+  //
+  // HasPendingManualCompaction() is true when at least one thread is inside
+  // RunManualCompaction(), i.e. during that time no other compaction will
+  // get scheduled (see MaybeScheduleFlushOrCompaction).
+  //
+  // Note that the following loop doesn't stop more that one thread calling
+  // RunManualCompaction() from getting to the second while loop below.
+  // However, only one of them will actually schedule compaction, while
+  // others will wait on a condition variable until it completes.
+
+  AddManualCompaction(&manual);
+  TEST_SYNC_POINT_CALLBACK("DBImpl::RunManualCompaction:NotScheduled", &mutex_);
+  if (exclusive) {
+    while (bg_bottom_compaction_scheduled_ > 0 ||
+           bg_compaction_scheduled_ > 0) {
+      TEST_SYNC_POINT("DBImpl::RunManualCompaction:WaitScheduled");
+      ROCKS_LOG_INFO(
+          immutable_db_options_.info_log,
+          "[%s] Manual compaction waiting for all other scheduled background "
+          "compactions to finish",
+          cfd->GetName().c_str());
+      bg_cv_.Wait();
+    }
+  }
+
+  ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                 "[%s] Manual compaction starting", cfd->GetName().c_str());
+
+  LogBuffer log_buffer(InfoLogLevel::INFO_LEVEL,
+                       immutable_db_options_.info_log.get());
+  // We don't check bg_error_ here, because if we get the error in compaction,
+  // the compaction will set manual.status to bg_error_ and set manual.done to
+  // true.
+  while (!manual.done) {
+    assert(HasPendingManualCompaction());
+    manual_conflict = false;
+    Compaction* compaction = nullptr;
+    if (ShouldntRunManualCompaction(&manual) || (manual.in_progress == true) ||
+        scheduled ||
+        (((manual.manual_end = &manual.tmp_storage1) != nullptr) &&
+         ((compaction = manual.cfd->CompactRange(
+               *manual.cfd->GetLatestMutableCFOptions(), manual.input_level,
+               manual.output_level, manual.output_path_id, max_subcompactions,
+               manual.begin, manual.end, &manual.manual_end,
+               &manual_conflict)) == nullptr &&
+          manual_conflict))) {
+      // exclusive manual compactions should not see a conflict during
+      // CompactRange
+      assert(!exclusive || !manual_conflict);
+      // Running either this or some other manual compaction
+      bg_cv_.Wait();
+      if (scheduled && manual.incomplete == true) {
+        assert(!manual.in_progress);
+        scheduled = false;
+        manual.incomplete = false;
+      }
+    } else if (!scheduled) {
+      if (compaction == nullptr) {
+        manual.done = true;
+        bg_cv_.SignalAll();
+        continue;
+      }
+      ca = new CompactionArg;
+      ca->db = this;
+      ca->prepicked_compaction = new PrepickedCompaction;
+      ca->prepicked_compaction->manual_compaction_state = &manual;
+      ca->prepicked_compaction->compaction = compaction;
+      if (!RequestCompactionToken(
+              cfd, true, &ca->prepicked_compaction->task_token, &log_buffer)) {
+        // Don't throttle manual compaction, only count outstanding tasks.
+        assert(false);
+      }
+      manual.incomplete = false;
+      bg_compaction_scheduled_++;
+      env_->Schedule(&DBImpl::BGWorkCompaction, ca, Env::Priority::LOW, this,
+                     &DBImpl::UnscheduleCompactionCallback);
+      scheduled = true;
+    }
+  }
+
+  log_buffer.FlushBufferToLog();
+  assert(!manual.in_progress);
+  assert(HasPendingManualCompaction());
+  RemoveManualCompaction(&manual);
+  bg_cv_.SignalAll();
+  return manual.status;
+}
+
+void DBImpl::GenerateFlushRequest(const autovector<ColumnFamilyData*>& cfds,
+                                  FlushRequest* req) {
+  assert(req != nullptr);
+  req->reserve(cfds.size());
+  for (const auto cfd : cfds) {
+    if (nullptr == cfd) {
+      // cfd may be null, see DBImpl::ScheduleFlushes
+      continue;
+    }
+    uint64_t max_memtable_id = cfd->imm()->GetLatestMemTableID();
+    req->emplace_back(cfd, max_memtable_id);
+  }
+}
+
+Status DBImpl::FlushMemTable(ColumnFamilyData* cfd,
+                             const FlushOptions& flush_options,
+                             FlushReason flush_reason, bool writes_stopped) {
+  Status s;
+  uint64_t flush_memtable_id = 0;
+  if (!flush_options.allow_write_stall) {
+    bool flush_needed = true;
+    s = WaitUntilFlushWouldNotStallWrites(cfd, &flush_needed);
+    TEST_SYNC_POINT("DBImpl::FlushMemTable:StallWaitDone");
+    if (!s.ok() || !flush_needed) {
+      return s;
+    }
+  }
+  FlushRequest flush_req;
+  {
+    WriteContext context;
+    InstrumentedMutexLock guard_lock(&mutex_);
+
+    WriteThread::Writer w;
+    if (!writes_stopped) {
+      write_thread_.EnterUnbatched(&w, &mutex_);
+    }
+
+    if (!cfd->mem()->IsEmpty() || !cached_recoverable_state_empty_.load()) {
+      s = SwitchMemtable(cfd, &context);
+    }
+
+    if (s.ok()) {
+      if (cfd->imm()->NumNotFlushed() != 0 || !cfd->mem()->IsEmpty() ||
+          !cached_recoverable_state_empty_.load()) {
+        flush_memtable_id = cfd->imm()->GetLatestMemTableID();
+        flush_req.emplace_back(cfd, flush_memtable_id);
+      }
+    }
+
+    if (s.ok() && !flush_req.empty()) {
+      for (auto& elem : flush_req) {
+        ColumnFamilyData* loop_cfd = elem.first;
+        loop_cfd->imm()->FlushRequested();
+      }
+      SchedulePendingFlush(flush_req, flush_reason);
+      MaybeScheduleFlushOrCompaction();
+    }
+
+    if (!writes_stopped) {
+      write_thread_.ExitUnbatched(&w);
+    }
+  }
+
+  if (s.ok() && flush_options.wait) {
+    autovector<ColumnFamilyData*> cfds;
+    autovector<const uint64_t*> flush_memtable_ids;
+    for (auto& iter : flush_req) {
+      cfds.push_back(iter.first);
+      flush_memtable_ids.push_back(&(iter.second));
+    }
+    s = WaitForFlushMemTables(cfds, flush_memtable_ids,
+                              (flush_reason == FlushReason::kErrorRecovery));
+  }
+  TEST_SYNC_POINT("FlushMemTableFinished");
+  return s;
+}
+
+// Flush all elments in 'column_family_datas'
+// and atomically record the result to the MANIFEST.
+Status DBImpl::AtomicFlushMemTables(
+    const autovector<ColumnFamilyData*>& column_family_datas,
+    const FlushOptions& flush_options, FlushReason flush_reason,
+    bool writes_stopped) {
+  Status s;
+  if (!flush_options.allow_write_stall) {
+    int num_cfs_to_flush = 0;
+    for (auto cfd : column_family_datas) {
+      bool flush_needed = true;
+      s = WaitUntilFlushWouldNotStallWrites(cfd, &flush_needed);
+      if (!s.ok()) {
+        return s;
+      } else if (flush_needed) {
+        ++num_cfs_to_flush;
+      }
+    }
+    if (0 == num_cfs_to_flush) {
+      return s;
+    }
+  }
+  FlushRequest flush_req;
+  autovector<ColumnFamilyData*> cfds;
+  {
+    WriteContext context;
+    InstrumentedMutexLock guard_lock(&mutex_);
+
+    WriteThread::Writer w;
+    if (!writes_stopped) {
+      write_thread_.EnterUnbatched(&w, &mutex_);
+    }
+
+    for (auto cfd : column_family_datas) {
+      if (cfd->IsDropped()) {
+        continue;
+      }
+      if (cfd->imm()->NumNotFlushed() != 0 || !cfd->mem()->IsEmpty() ||
+          !cached_recoverable_state_empty_.load()) {
+        cfds.emplace_back(cfd);
+      }
+    }
+    for (auto cfd : cfds) {
+      if (cfd->mem()->IsEmpty() && cached_recoverable_state_empty_.load()) {
+        continue;
+      }
+      cfd->Ref();
+      s = SwitchMemtable(cfd, &context);
+      cfd->Unref();
+      if (!s.ok()) {
+        break;
+      }
+    }
+    if (s.ok()) {
+      AssignAtomicFlushSeq(cfds);
+      for (auto cfd : cfds) {
+        cfd->imm()->FlushRequested();
+      }
+      GenerateFlushRequest(cfds, &flush_req);
+      SchedulePendingFlush(flush_req, flush_reason);
+      MaybeScheduleFlushOrCompaction();
+    }
+
+    if (!writes_stopped) {
+      write_thread_.ExitUnbatched(&w);
+    }
+  }
+  TEST_SYNC_POINT("DBImpl::AtomicFlushMemTables:AfterScheduleFlush");
+
+  if (s.ok() && flush_options.wait) {
+    autovector<const uint64_t*> flush_memtable_ids;
+    for (auto& iter : flush_req) {
+      flush_memtable_ids.push_back(&(iter.second));
+    }
+    s = WaitForFlushMemTables(cfds, flush_memtable_ids,
+                              (flush_reason == FlushReason::kErrorRecovery));
+  }
+  return s;
+}
+
+// Calling FlushMemTable(), whether from DB::Flush() or from Backup Engine, can
+// cause write stall, for example if one memtable is being flushed already.
+// This method tries to avoid write stall (similar to CompactRange() behavior)
+// it emulates how the SuperVersion / LSM would change if flush happens, checks
+// it against various constrains and delays flush if it'd cause write stall.
+// Called should check status and flush_needed to see if flush already happened.
+Status DBImpl::WaitUntilFlushWouldNotStallWrites(ColumnFamilyData* cfd,
+                                                 bool* flush_needed) {
+  {
+    *flush_needed = true;
+    InstrumentedMutexLock l(&mutex_);
+    uint64_t orig_active_memtable_id = cfd->mem()->GetID();
+    WriteStallCondition write_stall_condition = WriteStallCondition::kNormal;
+    do {
+      if (write_stall_condition != WriteStallCondition::kNormal) {
+        // Same error handling as user writes: Don't wait if there's a
+        // background error, even if it's a soft error. We might wait here
+        // indefinitely as the pending flushes/compactions may never finish
+        // successfully, resulting in the stall condition lasting indefinitely
+        if (error_handler_.IsBGWorkStopped()) {
+          return error_handler_.GetBGError();
+        }
+
+        TEST_SYNC_POINT("DBImpl::WaitUntilFlushWouldNotStallWrites:StallWait");
+        ROCKS_LOG_INFO(immutable_db_options_.info_log,
+                       "[%s] WaitUntilFlushWouldNotStallWrites"
+                       " waiting on stall conditions to clear",
+                       cfd->GetName().c_str());
+        bg_cv_.Wait();
+      }
+      if (cfd->IsDropped() || shutting_down_.load(std::memory_order_acquire)) {
+        return Status::ShutdownInProgress();
+      }
+
+      uint64_t earliest_memtable_id =
+          std::min(cfd->mem()->GetID(), cfd->imm()->GetEarliestMemTableID());
+      if (earliest_memtable_id > orig_active_memtable_id) {
+        // We waited so long that the memtable we were originally waiting on was
+        // flushed.
+        *flush_needed = false;
+        return Status::OK();
+      }
+
+      const auto& mutable_cf_options = *cfd->GetLatestMutableCFOptions();
+      const auto* vstorage = cfd->current()->storage_info();
+
+      // Skip stalling check if we're below auto-flush and auto-compaction
+      // triggers. If it stalled in these conditions, that'd mean the stall
+      // triggers are so low that stalling is needed for any background work. In
+      // that case we shouldn't wait since background work won't be scheduled.
+      if (cfd->imm()->NumNotFlushed() <
+              cfd->ioptions()->min_write_buffer_number_to_merge &&
+          vstorage->l0_delay_trigger_count() <
+              mutable_cf_options.level0_file_num_compaction_trigger) {
+        break;
+      }
+
+      // check whether one extra immutable memtable or an extra L0 file would
+      // cause write stalling mode to be entered. It could still enter stall
+      // mode due to pending compaction bytes, but that's less common
+      write_stall_condition =
+          ColumnFamilyData::GetWriteStallConditionAndCause(
+              cfd->imm()->NumNotFlushed() + 1,
+              vstorage->l0_delay_trigger_count() + 1,
+              vstorage->estimated_compaction_needed_bytes(), mutable_cf_options)
+              .first;
+    } while (write_stall_condition != WriteStallCondition::kNormal);
+  }
+  return Status::OK();
+}
+
+// Wait for memtables to be flushed for multiple column families.
+// let N = cfds.size()
+// for i in [0, N),
+//  1) if flush_memtable_ids[i] is not null, then the memtables with lower IDs
+//     have to be flushed for THIS column family;
+//  2) if flush_memtable_ids[i] is null, then all memtables in THIS column
+//     family have to be flushed.
+// Finish waiting when ALL column families finish flushing memtables.
+// resuming_from_bg_err indicates whether the caller is trying to resume from
+// background error or in normal processing.
+Status DBImpl::WaitForFlushMemTables(
+    const autovector<ColumnFamilyData*>& cfds,
+    const autovector<const uint64_t*>& flush_memtable_ids,
+    bool resuming_from_bg_err) {
+  int num = static_cast<int>(cfds.size());
+  // Wait until the compaction completes
+  InstrumentedMutexLock l(&mutex_);
+  // If the caller is trying to resume from bg error, then
+  // error_handler_.IsDBStopped() is true.
+  while (resuming_from_bg_err || !error_handler_.IsDBStopped()) {
+    if (shutting_down_.load(std::memory_order_acquire)) {
+      return Status::ShutdownInProgress();
+    }
+    // If an error has occurred during resumption, then no need to wait.
+    if (!error_handler_.GetRecoveryError().ok()) {
+      break;
+    }
+    // Number of column families that have been dropped.
+    int num_dropped = 0;
+    // Number of column families that have finished flush.
+    int num_finished = 0;
+    for (int i = 0; i < num; ++i) {
+      if (cfds[i]->IsDropped()) {
+        ++num_dropped;
+      } else if (cfds[i]->imm()->NumNotFlushed() == 0 ||
+                 (flush_memtable_ids[i] != nullptr &&
+                  cfds[i]->imm()->GetEarliestMemTableID() >
+                      *flush_memtable_ids[i])) {
+        ++num_finished;
+      }
+    }
+    if (1 == num_dropped && 1 == num) {
+      return Status::InvalidArgument("Cannot flush a dropped CF");
+    }
+    // Column families involved in this flush request have either been dropped
+    // or finished flush. Then it's time to finish waiting.
+    if (num_dropped + num_finished == num) {
+      break;
+    }
+    bg_cv_.Wait();
+  }
+  Status s;
+  // If not resuming from bg error, and an error has caused the DB to stop,
+  // then report the bg error to caller.
+  if (!resuming_from_bg_err && error_handler_.IsDBStopped()) {
+    s = error_handler_.GetBGError();
+  }
+  return s;
+}
+
+Status DBImpl::EnableAutoCompaction(
+    const std::vector<ColumnFamilyHandle*>& column_family_handles) {
+  Status s;
+  for (auto cf_ptr : column_family_handles) {
+    Status status =
+        this->SetOptions(cf_ptr, {{"disable_auto_compactions", "false"}});
+    if (!status.ok()) {
+      s = status;
+    }
+  }
+
+  return s;
+}
+
+void DBImpl::MaybeScheduleFlushOrCompaction() {
+  mutex_.AssertHeld();
+  if (!opened_successfully_) {
+    // Compaction may introduce data race to DB open
+    return;
+  }
+  if (bg_work_paused_ > 0) {
+    // we paused the background work
+    return;
+  } else if (error_handler_.IsBGWorkStopped() &&
+             !error_handler_.IsRecoveryInProgress()) {
+    // There has been a hard error and this call is not part of the recovery
+    // sequence. Bail out here so we don't get into an endless loop of
+    // scheduling BG work which will again call this function
+    return;
+  } else if (shutting_down_.load(std::memory_order_acquire)) {
+    // DB is being deleted; no more background compactions
+    return;
+  }
+  auto bg_job_limits = GetBGJobLimits();
+  bool is_flush_pool_empty =
+      env_->GetBackgroundThreads(Env::Priority::HIGH) == 0;
+  while (!is_flush_pool_empty && unscheduled_flushes_ > 0 &&
+         bg_flush_scheduled_ < bg_job_limits.max_flushes) {
+    bg_flush_scheduled_++;
+    FlushThreadArg* fta = new FlushThreadArg;
+    fta->db_ = this;
+    fta->thread_pri_ = Env::Priority::HIGH;
+    env_->Schedule(&DBImpl::BGWorkFlush, fta, Env::Priority::HIGH, this,
+                   &DBImpl::UnscheduleFlushCallback);
+  }
+
+  // special case -- if high-pri (flush) thread pool is empty, then schedule
+  // flushes in low-pri (compaction) thread pool.
+  if (is_flush_pool_empty) {
+    while (unscheduled_flushes_ > 0 &&
+           bg_flush_scheduled_ + bg_compaction_scheduled_ <
+               bg_job_limits.max_flushes) {
+      bg_flush_scheduled_++;
+      FlushThreadArg* fta = new FlushThreadArg;
+      fta->db_ = this;
+      fta->thread_pri_ = Env::Priority::LOW;
+      env_->Schedule(&DBImpl::BGWorkFlush, fta, Env::Priority::LOW, this,
+                     &DBImpl::UnscheduleFlushCallback);
+    }
+  }
+
+  if (bg_compaction_paused_ > 0) {
+    // we paused the background compaction
+    return;
+  } else if (error_handler_.IsBGWorkStopped()) {
+    // Compaction is not part of the recovery sequence from a hard error. We
+    // might get here because recovery might do a flush and install a new
+    // super version, which will try to schedule pending compactions. Bail
+    // out here and let the higher level recovery handle compactions
+    return;
+  }
+
+  if (HasExclusiveManualCompaction()) {
+    // only manual compactions are allowed to run. don't schedule automatic
+    // compactions
+    TEST_SYNC_POINT("DBImpl::MaybeScheduleFlushOrCompaction:Conflict");
+    return;
+  }
+
+  while (bg_compaction_scheduled_ < bg_job_limits.max_compactions &&
+         unscheduled_compactions_ > 0) {
+    CompactionArg* ca = new CompactionArg;
+    ca->db = this;
+    ca->prepicked_compaction = nullptr;
+    bg_compaction_scheduled_++;
+    unscheduled_compactions_--;
+    env_->Schedule(&DBImpl::BGWorkCompaction, ca, Env::Priority::LOW, this,
+                   &DBImpl::UnscheduleCompactionCallback);
+  }
+}
+
+DBImpl::BGJobLimits DBImpl::GetBGJobLimits() const {
+  mutex_.AssertHeld();
+  return GetBGJobLimits(immutable_db_options_.max_background_flushes,
+                        mutable_db_options_.max_background_compactions,
+                        mutable_db_options_.max_background_jobs,
+                        write_controller_.NeedSpeedupCompaction());
+}
+
+DBImpl::BGJobLimits DBImpl::GetBGJobLimits(int max_background_flushes,
+                                           int max_background_compactions,
+                                           int max_background_jobs,
+                                           bool parallelize_compactions) {
+  BGJobLimits res;
+  if (max_background_flushes == -1 && max_background_compactions == -1) {
+    // for our first stab implementing max_background_jobs, simply allocate a
+    // quarter of the threads to flushes.
+    res.max_flushes = std::max(1, max_background_jobs / 4);
+    res.max_compactions = std::max(1, max_background_jobs - res.max_flushes);
+  } else {
+    // compatibility code in case users haven't migrated to max_background_jobs,
+    // which automatically computes flush/compaction limits
+    res.max_flushes = std::max(1, max_background_flushes);
+    res.max_compactions = std::max(1, max_background_compactions);
+  }
+  if (!parallelize_compactions) {
+    // throttle background compactions until we deem necessary
+    res.max_compactions = 1;
+  }
+  return res;
+}
+
+void DBImpl::AddToCompactionQueue(ColumnFamilyData* cfd) {
+  assert(!cfd->queued_for_compaction());
+  cfd->Ref();
+  compaction_queue_.push_back(cfd);
+  cfd->set_queued_for_compaction(true);
+}
+
+ColumnFamilyData* DBImpl::PopFirstFromCompactionQueue() {
+  assert(!compaction_queue_.empty());
+  auto cfd = *compaction_queue_.begin();
+  compaction_queue_.pop_front();
+  assert(cfd->queued_for_compaction());
+  cfd->set_queued_for_compaction(false);
+  return cfd;
+}
+
+DBImpl::FlushRequest DBImpl::PopFirstFromFlushQueue() {
+  assert(!flush_queue_.empty());
+  FlushRequest flush_req = flush_queue_.front();
+  assert(unscheduled_flushes_ >= static_cast<int>(flush_req.size()));
+  unscheduled_flushes_ -= static_cast<int>(flush_req.size());
+  flush_queue_.pop_front();
+  // TODO: need to unset flush reason?
+  return flush_req;
+}
+
+ColumnFamilyData* DBImpl::PickCompactionFromQueue(
+    std::unique_ptr<TaskLimiterToken>* token, LogBuffer* log_buffer) {
+  assert(!compaction_queue_.empty());
+  assert(*token == nullptr);
+  autovector<ColumnFamilyData*> throttled_candidates;
+  ColumnFamilyData* cfd = nullptr;
+  while (!compaction_queue_.empty()) {
+    auto first_cfd = *compaction_queue_.begin();
+    compaction_queue_.pop_front();
+    assert(first_cfd->queued_for_compaction());
+    if (!RequestCompactionToken(first_cfd, false, token, log_buffer)) {
+      throttled_candidates.push_back(first_cfd);
+      continue;
+    }
+    cfd = first_cfd;
+    cfd->set_queued_for_compaction(false);
+    break;
+  }
+  // Add throttled compaction candidates back to queue in the original order.
+  for (auto iter = throttled_candidates.rbegin();
+       iter != throttled_candidates.rend(); ++iter) {
+    compaction_queue_.push_front(*iter);
+  }
+  return cfd;
+}
+
+void DBImpl::SchedulePendingFlush(const FlushRequest& flush_req,
+                                  FlushReason flush_reason) {
+  if (flush_req.empty()) {
+    return;
+  }
+  for (auto& iter : flush_req) {
+    ColumnFamilyData* cfd = iter.first;
+    cfd->Ref();
+    cfd->SetFlushReason(flush_reason);
+  }
+  unscheduled_flushes_ += static_cast<int>(flush_req.size());
+  flush_queue_.push_back(flush_req);
+}
+
+void DBImpl::SchedulePendingCompaction(ColumnFamilyData* cfd) {
+  if (!cfd->queued_for_compaction() && cfd->NeedsCompaction()) {
+    AddToCompactionQueue(cfd);
+    ++unscheduled_compactions_;
+  }
+}
+
+void DBImpl::SchedulePendingPurge(std::string fname, std::string dir_to_sync,
+                                  FileType type, uint64_t number, int job_id) {
+  mutex_.AssertHeld();
+  PurgeFileInfo file_info(fname, dir_to_sync, type, number, job_id);
+  purge_queue_.push_back(std::move(file_info));
+}
+
+void DBImpl::BGWorkFlush(void* arg) {
+  FlushThreadArg fta = *(reinterpret_cast<FlushThreadArg*>(arg));
+  delete reinterpret_cast<FlushThreadArg*>(arg);
+
+  IOSTATS_SET_THREAD_POOL_ID(fta.thread_pri_);
+  TEST_SYNC_POINT("DBImpl::BGWorkFlush");
+  reinterpret_cast<DBImpl*>(fta.db_)->BackgroundCallFlush(fta.thread_pri_);
+  TEST_SYNC_POINT("DBImpl::BGWorkFlush:done");
+}
+
+void DBImpl::BGWorkCompaction(void* arg) {
+  CompactionArg ca = *(reinterpret_cast<CompactionArg*>(arg));
+  delete reinterpret_cast<CompactionArg*>(arg);
+  IOSTATS_SET_THREAD_POOL_ID(Env::Priority::LOW);
+  TEST_SYNC_POINT("DBImpl::BGWorkCompaction");
+  auto prepicked_compaction =
+      static_cast<PrepickedCompaction*>(ca.prepicked_compaction);
+  reinterpret_cast<DBImpl*>(ca.db)->BackgroundCallCompaction(
+      prepicked_compaction, Env::Priority::LOW);
+  delete prepicked_compaction;
+}
+
+void DBImpl::BGWorkBottomCompaction(void* arg) {
+  CompactionArg ca = *(static_cast<CompactionArg*>(arg));
+  delete static_cast<CompactionArg*>(arg);
+  IOSTATS_SET_THREAD_POOL_ID(Env::Priority::BOTTOM);
+  TEST_SYNC_POINT("DBImpl::BGWorkBottomCompaction");
+  auto* prepicked_compaction = ca.prepicked_compaction;
+  assert(prepicked_compaction && prepicked_compaction->compaction &&
+         !prepicked_compaction->manual_compaction_state);
+  ca.db->BackgroundCallCompaction(prepicked_compaction, Env::Priority::BOTTOM);
+  delete prepicked_compaction;
+}
+
+void DBImpl::BGWorkPurge(void* db) {
+  IOSTATS_SET_THREAD_POOL_ID(Env::Priority::HIGH);
+  TEST_SYNC_POINT("DBImpl::BGWorkPurge:start");
+  reinterpret_cast<DBImpl*>(db)->BackgroundCallPurge();
+  TEST_SYNC_POINT("DBImpl::BGWorkPurge:end");
+}
+
+void DBImpl::UnscheduleCompactionCallback(void* arg) {
+  CompactionArg ca = *(reinterpret_cast<CompactionArg*>(arg));
+  delete reinterpret_cast<CompactionArg*>(arg);
+  if (ca.prepicked_compaction != nullptr) {
+    if (ca.prepicked_compaction->compaction != nullptr) {
+      delete ca.prepicked_compaction->compaction;
+    }
+    delete ca.prepicked_compaction;
+  }
+  TEST_SYNC_POINT("DBImpl::UnscheduleCompactionCallback");
+}
+
+void DBImpl::UnscheduleFlushCallback(void* arg) {
+  delete reinterpret_cast<FlushThreadArg*>(arg);
+  TEST_SYNC_POINT("DBImpl::UnscheduleFlushCallback");
+}
+
+Status DBImpl::BackgroundFlush(bool* made_progress, JobContext* job_context,
+                               LogBuffer* log_buffer, FlushReason* reason,
+                               Env::Priority thread_pri) {
+  mutex_.AssertHeld();
+
+  Status status;
+  *reason = FlushReason::kOthers;
+  // If BG work is stopped due to an error, but a recovery is in progress,
+  // that means this flush is part of the recovery. So allow it to go through
+  if (!error_handler_.IsBGWorkStopped()) {
+    if (shutting_down_.load(std::memory_order_acquire)) {
+      status = Status::ShutdownInProgress();
+    }
+  } else if (!error_handler_.IsRecoveryInProgress()) {
+    status = error_handler_.GetBGError();
+  }
+
+  if (!status.ok()) {
+    return status;
+  }
+
+  autovector<BGFlushArg> bg_flush_args;
+  std::vector<SuperVersionContext>& superversion_contexts =
+      job_context->superversion_contexts;
+  while (!flush_queue_.empty()) {
+    // This cfd is already referenced
+    const FlushRequest& flush_req = PopFirstFromFlushQueue();
+    superversion_contexts.clear();
+    superversion_contexts.reserve(flush_req.size());
+
+    for (const auto& iter : flush_req) {
+      ColumnFamilyData* cfd = iter.first;
+      if (cfd->IsDropped() || !cfd->imm()->IsFlushPending()) {
+        // can't flush this CF, try next one
+        if (cfd->Unref()) {
+          delete cfd;
+        }
+        continue;
+      }
+      superversion_contexts.emplace_back(SuperVersionContext(true));
+      bg_flush_args.emplace_back(cfd, iter.second,
+                                 &(superversion_contexts.back()));
+    }
+    if (!bg_flush_args.empty()) {
+      break;
+    }
+  }
+
+  if (!bg_flush_args.empty()) {
+    auto bg_job_limits = GetBGJobLimits();
+    for (const auto& arg : bg_flush_args) {
+      ColumnFamilyData* cfd = arg.cfd_;
+      ROCKS_LOG_BUFFER(
+          log_buffer,
+          "Calling FlushMemTableToOutputFile with column "
+          "family [%s], flush slots available %d, compaction slots available "
+          "%d, "
+          "flush slots scheduled %d, compaction slots scheduled %d",
+          cfd->GetName().c_str(), bg_job_limits.max_flushes,
+          bg_job_limits.max_compactions, bg_flush_scheduled_,
+          bg_compaction_scheduled_);
+    }
+    status = FlushMemTablesToOutputFiles(bg_flush_args, made_progress,
+                                         job_context, log_buffer, thread_pri);
+    // All the CFDs in the FlushReq must have the same flush reason, so just
+    // grab the first one
+    *reason = bg_flush_args[0].cfd_->GetFlushReason();
+    for (auto& arg : bg_flush_args) {
+      ColumnFamilyData* cfd = arg.cfd_;
+      if (cfd->Unref()) {
+        delete cfd;
+        arg.cfd_ = nullptr;
+      }
+    }
+  }
+  return status;
+}
+
+void DBImpl::BackgroundCallFlush(Env::Priority thread_pri) {
+  bool made_progress = false;
+  JobContext job_context(next_job_id_.fetch_add(1), true);
+
+  TEST_SYNC_POINT("DBImpl::BackgroundCallFlush:start");
+
+  LogBuffer log_buffer(InfoLogLevel::INFO_LEVEL,
+                       immutable_db_options_.info_log.get());
+  {
+    InstrumentedMutexLock l(&mutex_);
+    assert(bg_flush_scheduled_);
+    num_running_flushes_++;
+
+    auto pending_outputs_inserted_elem =
+        CaptureCurrentFileNumberInPendingOutputs();
+    FlushReason reason;
+
+    Status s = BackgroundFlush(&made_progress, &job_context, &log_buffer,
+                               &reason, thread_pri);
+    if (!s.ok() && !s.IsShutdownInProgress() &&
+        reason != FlushReason::kErrorRecovery) {
+      // Wait a little bit before retrying background flush in
+      // case this is an environmental problem and we do not want to
+      // chew up resources for failed flushes for the duration of
+      // the problem.
+      uint64_t error_cnt =
+          default_cf_internal_stats_->BumpAndGetBackgroundErrorCount();
+      bg_cv_.SignalAll();  // In case a waiter can proceed despite the error
+      mutex_.Unlock();
+      ROCKS_LOG_ERROR(immutable_db_options_.info_log,
+                      "Waiting after background flush error: %s"
+                      "Accumulated background error counts: %" PRIu64,
+                      s.ToString().c_str(), error_cnt);
+      log_buffer.FlushBufferToLog();
+      LogFlush(immutable_db_options_.info_log);
+      env_->SleepForMicroseconds(1000000);
+      mutex_.Lock();
+    }
+
+    TEST_SYNC_POINT("DBImpl::BackgroundCallFlush:FlushFinish:0");
+    ReleaseFileNumberFromPendingOutputs(pending_outputs_inserted_elem);
+
+    // If flush failed, we want to delete all temporary files that we might have
+    // created. Thus, we force full scan in FindObsoleteFiles()
+    FindObsoleteFiles(&job_context, !s.ok() && !s.IsShutdownInProgress());
+    // delete unnecessary files if any, this is done outside the mutex
+    if (job_context.HaveSomethingToClean() ||
+        job_context.HaveSomethingToDelete() || !log_buffer.IsEmpty()) {
+      mutex_.Unlock();
+      TEST_SYNC_POINT("DBImpl::BackgroundCallFlush:FilesFound");
+      // Have to flush the info logs before bg_flush_scheduled_--
+      // because if bg_flush_scheduled_ becomes 0 and the lock is
+      // released, the deconstructor of DB can kick in and destroy all the
+      // states of DB so info_log might not be available after that point.
+      // It also applies to access other states that DB owns.
+      log_buffer.FlushBufferToLog();
+      if (job_context.HaveSomethingToDelete()) {
+        PurgeObsoleteFiles(job_context);
+      }
+      job_context.Clean();
+      mutex_.Lock();
+    }
+    TEST_SYNC_POINT("DBImpl::BackgroundCallFlush:ContextCleanedUp");
+
+    assert(num_running_flushes_ > 0);
+    num_running_flushes_--;
+    bg_flush_scheduled_--;
+    // See if there's more work to be done
+    MaybeScheduleFlushOrCompaction();
+    atomic_flush_install_cv_.SignalAll();
+    bg_cv_.SignalAll();
+    // IMPORTANT: there should be no code after calling SignalAll. This call may
+    // signal the DB destructor that it's OK to proceed with destruction. In
+    // that case, all DB variables will be dealloacated and referencing them
+    // will cause trouble.
+  }
+}
+
+void DBImpl::BackgroundCallCompaction(PrepickedCompaction* prepicked_compaction,
+                                      Env::Priority bg_thread_pri) {
+  bool made_progress = false;
+  JobContext job_context(next_job_id_.fetch_add(1), true);
+  TEST_SYNC_POINT("BackgroundCallCompaction:0");
+  LogBuffer log_buffer(InfoLogLevel::INFO_LEVEL,
+                       immutable_db_options_.info_log.get());
+  {
+    InstrumentedMutexLock l(&mutex_);
+
+    // This call will unlock/lock the mutex to wait for current running
+    // IngestExternalFile() calls to finish.
+    WaitForIngestFile();
+
+    num_running_compactions_++;
+
+    auto pending_outputs_inserted_elem =
+        CaptureCurrentFileNumberInPendingOutputs();
+
+    assert((bg_thread_pri == Env::Priority::BOTTOM &&
+            bg_bottom_compaction_scheduled_) ||
+           (bg_thread_pri == Env::Priority::LOW && bg_compaction_scheduled_));
+    Status s = BackgroundCompaction(&made_progress, &job_context, &log_buffer,
+                                    prepicked_compaction, bg_thread_pri);
+    TEST_SYNC_POINT("BackgroundCallCompaction:1");
+    if (s.IsBusy()) {
+      bg_cv_.SignalAll();  // In case a waiter can proceed despite the error
+      mutex_.Unlock();
+      env_->SleepForMicroseconds(10000);  // prevent hot loop
+      mutex_.Lock();
+    } else if (!s.ok() && !s.IsShutdownInProgress()) {
+      // Wait a little bit before retrying background compaction in
+      // case this is an environmental problem and we do not want to
+      // chew up resources for failed compactions for the duration of
+      // the problem.
+      uint64_t error_cnt =
+          default_cf_internal_stats_->BumpAndGetBackgroundErrorCount();
+      bg_cv_.SignalAll();  // In case a waiter can proceed despite the error
+      mutex_.Unlock();
+      log_buffer.FlushBufferToLog();
+      ROCKS_LOG_ERROR(immutable_db_options_.info_log,
+                      "Waiting after background compaction error: %s, "
+                      "Accumulated background error counts: %" PRIu64,
+                      s.ToString().c_str(), error_cnt);
+      LogFlush(immutable_db_options_.info_log);
+      env_->SleepForMicroseconds(1000000);
+      mutex_.Lock();
+    }
+
+    ReleaseFileNumberFromPendingOutputs(pending_outputs_inserted_elem);
+
+    // If compaction failed, we want to delete all temporary files that we might
+    // have created (they might not be all recorded in job_context in case of a
+    // failure). Thus, we force full scan in FindObsoleteFiles()
+    FindObsoleteFiles(&job_context, !s.ok() && !s.IsShutdownInProgress());
+    TEST_SYNC_POINT("DBImpl::BackgroundCallCompaction:FoundObsoleteFiles");
+
+    // delete unnecessary files if any, this is done outside the mutex
+    if (job_context.HaveSomethingToClean() ||
+        job_context.HaveSomethingToDelete() || !log_buffer.IsEmpty()) {
+      mutex_.Unlock();
+      // Have to flush the info logs before bg_compaction_scheduled_--
+      // because if bg_flush_scheduled_ becomes 0 and the lock is
+      // released, the deconstructor of DB can kick in and destroy all the
+      // states of DB so info_log might not be available after that point.
+      // It also applies to access other states that DB owns.
+      log_buffer.FlushBufferToLog();
+      if (job_context.HaveSomethingToDelete()) {
+        PurgeObsoleteFiles(job_context);
+        TEST_SYNC_POINT("DBImpl::BackgroundCallCompaction:PurgedObsoleteFiles");
+      }
+      job_context.Clean();
+      mutex_.Lock();
+    }
+
+    assert(num_running_compactions_ > 0);
+    num_running_compactions_--;
+    if (bg_thread_pri == Env::Priority::LOW) {
+      bg_compaction_scheduled_--;
+    } else {
+      assert(bg_thread_pri == Env::Priority::BOTTOM);
+      bg_bottom_compaction_scheduled_--;
+    }
+
+    versions_->GetColumnFamilySet()->FreeDeadColumnFamilies();
+
+    // See if there's more work to be done
+    MaybeScheduleFlushOrCompaction();
+    if (made_progress ||
+        (bg_compaction_scheduled_ == 0 &&
+         bg_bottom_compaction_scheduled_ == 0) ||
+        HasPendingManualCompaction() || unscheduled_compactions_ == 0) {
+      // signal if
+      // * made_progress -- need to wakeup DelayWrite
+      // * bg_{bottom,}_compaction_scheduled_ == 0 -- need to wakeup ~DBImpl
+      // * HasPendingManualCompaction -- need to wakeup RunManualCompaction
+      // If none of this is true, there is no need to signal since nobody is
+      // waiting for it
+      bg_cv_.SignalAll();
+    }
+    // IMPORTANT: there should be no code after calling SignalAll. This call may
+    // signal the DB destructor that it's OK to proceed with destruction. In
+    // that case, all DB variables will be dealloacated and referencing them
+    // will cause trouble.
+  }
+}
+
+Status DBImpl::BackgroundCompaction(bool* made_progress,
+                                    JobContext* job_context,
+                                    LogBuffer* log_buffer,
+                                    PrepickedCompaction* prepicked_compaction,
+                                    Env::Priority thread_pri) {
+  ManualCompactionState* manual_compaction =
+      prepicked_compaction == nullptr
+          ? nullptr
+          : prepicked_compaction->manual_compaction_state;
+  *made_progress = false;
+  mutex_.AssertHeld();
+  TEST_SYNC_POINT("DBImpl::BackgroundCompaction:Start");
+
+  bool is_manual = (manual_compaction != nullptr);
+  std::unique_ptr<Compaction> c;
+  if (prepicked_compaction != nullptr &&
+      prepicked_compaction->compaction != nullptr) {
+    c.reset(prepicked_compaction->compaction);
+  }
+  bool is_prepicked = is_manual || c;
+
+  // (manual_compaction->in_progress == false);
+  bool trivial_move_disallowed =
+      is_manual && manual_compaction->disallow_trivial_move;
+
+  CompactionJobStats compaction_job_stats;
+  Status status;
+  if (!error_handler_.IsBGWorkStopped()) {
+    if (shutting_down_.load(std::memory_order_acquire)) {
+      status = Status::ShutdownInProgress();
+    }
+  } else {
+    status = error_handler_.GetBGError();
+    // If we get here, it means a hard error happened after this compaction
+    // was scheduled by MaybeScheduleFlushOrCompaction(), but before it got
+    // a chance to execute. Since we didn't pop a cfd from the compaction
+    // queue, increment unscheduled_compactions_
+    unscheduled_compactions_++;
+  }
+
+  if (!status.ok()) {
+    if (is_manual) {
+      manual_compaction->status = status;
+      manual_compaction->done = true;
+      manual_compaction->in_progress = false;
+      manual_compaction = nullptr;
+    }
+    if (c) {
+      c->ReleaseCompactionFiles(status);
+      c.reset();
+    }
+    return status;
+  }
+
+  if (is_manual) {
+    // another thread cannot pick up the same work
+    manual_compaction->in_progress = true;
+  }
+
+  std::unique_ptr<TaskLimiterToken> task_token;
+
+  // InternalKey manual_end_storage;
+  // InternalKey* manual_end = &manual_end_storage;
+  bool sfm_reserved_compact_space = false;
+  if (is_manual) {
+    ManualCompactionState* m = manual_compaction;
+    assert(m->in_progress);
+    if (!c) {
+      m->done = true;
+      m->manual_end = nullptr;
+      ROCKS_LOG_BUFFER(log_buffer,
+                       "[%s] Manual compaction from level-%d from %s .. "
+                       "%s; nothing to do\n",
+                       m->cfd->GetName().c_str(), m->input_level,
+                       (m->begin ? m->begin->DebugString().c_str() : "(begin)"),
+                       (m->end ? m->end->DebugString().c_str() : "(end)"));
+    } else {
+      // First check if we have enough room to do the compaction
+      bool enough_room = EnoughRoomForCompaction(
+          m->cfd, *(c->inputs()), &sfm_reserved_compact_space, log_buffer);
+
+      if (!enough_room) {
+        // Then don't do the compaction
+        c->ReleaseCompactionFiles(status);
+        c.reset();
+        // m's vars will get set properly at the end of this function,
+        // as long as status == CompactionTooLarge
+        status = Status::CompactionTooLarge();
+      } else {
+        ROCKS_LOG_BUFFER(
+            log_buffer,
+            "[%s] Manual compaction from level-%d to level-%d from %s .. "
+            "%s; will stop at %s\n",
+            m->cfd->GetName().c_str(), m->input_level, c->output_level(),
+            (m->begin ? m->begin->DebugString().c_str() : "(begin)"),
+            (m->end ? m->end->DebugString().c_str() : "(end)"),
+            ((m->done || m->manual_end == nullptr)
+                 ? "(end)"
+                 : m->manual_end->DebugString().c_str()));
+      }
+    }
+  } else if (!is_prepicked && !compaction_queue_.empty()) {
+    if (HasExclusiveManualCompaction()) {
+      // Can't compact right now, but try again later
+      TEST_SYNC_POINT("DBImpl::BackgroundCompaction()::Conflict");
+
+      // Stay in the compaction queue.
+      unscheduled_compactions_++;
+
+      return Status::OK();
+    }
+
+    auto cfd = PickCompactionFromQueue(&task_token, log_buffer);
+    if (cfd == nullptr) {
+      // Can't find any executable task from the compaction queue.
+      // All tasks have been throttled by compaction thread limiter.
+      ++unscheduled_compactions_;
+      return Status::Busy();
+    }
+
+    // We unreference here because the following code will take a Ref() on
+    // this cfd if it is going to use it (Compaction class holds a
+    // reference).
+    // This will all happen under a mutex so we don't have to be afraid of
+    // somebody else deleting it.
+    if (cfd->Unref()) {
+      // This was the last reference of the column family, so no need to
+      // compact.
+      delete cfd;
+      return Status::OK();
+    }
+
+    // Pick up latest mutable CF Options and use it throughout the
+    // compaction job
+    // Compaction makes a copy of the latest MutableCFOptions. It should be used
+    // throughout the compaction procedure to make sure consistency. It will
+    // eventually be installed into SuperVersion
+    auto* mutable_cf_options = cfd->GetLatestMutableCFOptions();
+    if (!mutable_cf_options->disable_auto_compactions && !cfd->IsDropped()) {
+      // NOTE: try to avoid unnecessary copy of MutableCFOptions if
+      // compaction is not necessary. Need to make sure mutex is held
+      // until we make a copy in the following code
+      TEST_SYNC_POINT("DBImpl::BackgroundCompaction():BeforePickCompaction");
+      c.reset(cfd->PickCompaction(*mutable_cf_options, log_buffer));
+      TEST_SYNC_POINT("DBImpl::BackgroundCompaction():AfterPickCompaction");
+
+      if (c != nullptr) {
+        bool enough_room = EnoughRoomForCompaction(
+            cfd, *(c->inputs()), &sfm_reserved_compact_space, log_buffer);
+
+        if (!enough_room) {
+          // Then don't do the compaction
+          c->ReleaseCompactionFiles(status);
+          c->column_family_data()
+              ->current()
+              ->storage_info()
+              ->ComputeCompactionScore(*(c->immutable_cf_options()),
+                                       *(c->mutable_cf_options()));
+          AddToCompactionQueue(cfd);
+          ++unscheduled_compactions_;
+
+          c.reset();
+          // Don't need to sleep here, because BackgroundCallCompaction
+          // will sleep if !s.ok()
+          status = Status::CompactionTooLarge();
+        } else {
+          // update statistics
+          RecordInHistogram(stats_, NUM_FILES_IN_SINGLE_COMPACTION,
+                            c->inputs(0)->size());
+          // There are three things that can change compaction score:
+          // 1) When flush or compaction finish. This case is covered by
+          // InstallSuperVersionAndScheduleWork
+          // 2) When MutableCFOptions changes. This case is also covered by
+          // InstallSuperVersionAndScheduleWork, because this is when the new
+          // options take effect.
+          // 3) When we Pick a new compaction, we "remove" those files being
+          // compacted from the calculation, which then influences compaction
+          // score. Here we check if we need the new compaction even without the
+          // files that are currently being compacted. If we need another
+          // compaction, we might be able to execute it in parallel, so we add
+          // it to the queue and schedule a new thread.
+          if (cfd->NeedsCompaction()) {
+            // Yes, we need more compactions!
+            AddToCompactionQueue(cfd);
+            ++unscheduled_compactions_;
+            MaybeScheduleFlushOrCompaction();
+          }
+        }
+      }
+    }
+  }
+
+  if (!c) {
+    // Nothing to do
+    ROCKS_LOG_BUFFER(log_buffer, "Compaction nothing to do");
+  } else if (c->deletion_compaction()) {
+    // TODO(icanadi) Do we want to honor snapshots here? i.e. not delete old
+    // file if there is alive snapshot pointing to it
+    TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:BeforeCompaction",
+                             c->column_family_data());
+    assert(c->num_input_files(1) == 0);
+    assert(c->level() == 0);
+    assert(c->column_family_data()->ioptions()->compaction_style ==
+           kCompactionStyleFIFO);
+
+    compaction_job_stats.num_input_files = c->num_input_files(0);
+
+    NotifyOnCompactionBegin(c->column_family_data(), c.get(), status,
+                            compaction_job_stats, job_context->job_id);
+
+    for (const auto& f : *c->inputs(0)) {
+      c->edit()->DeleteFile(c->level(), f->fd.GetNumber());
+    }
+    status = versions_->LogAndApply(c->column_family_data(),
+                                    *c->mutable_cf_options(), c->edit(),
+                                    &mutex_, directories_.GetDbDir());
+    InstallSuperVersionAndScheduleWork(c->column_family_data(),
+                                       &job_context->superversion_contexts[0],
+                                       *c->mutable_cf_options());
+    ROCKS_LOG_BUFFER(log_buffer, "[%s] Deleted %d files\n",
+                     c->column_family_data()->GetName().c_str(),
+                     c->num_input_files(0));
+    *made_progress = true;
+    TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:AfterCompaction",
+                             c->column_family_data());
+  } else if (!trivial_move_disallowed && c->IsTrivialMove()) {
+    TEST_SYNC_POINT("DBImpl::BackgroundCompaction:TrivialMove");
+    TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:BeforeCompaction",
+                             c->column_family_data());
+    // Instrument for event update
+    // TODO(yhchiang): add op details for showing trivial-move.
+    ThreadStatusUtil::SetColumnFamily(
+        c->column_family_data(), c->column_family_data()->ioptions()->env,
+        immutable_db_options_.enable_thread_tracking);
+    ThreadStatusUtil::SetThreadOperation(ThreadStatus::OP_COMPACTION);
+
+    compaction_job_stats.num_input_files = c->num_input_files(0);
+
+    NotifyOnCompactionBegin(c->column_family_data(), c.get(), status,
+                            compaction_job_stats, job_context->job_id);
+
+    // Move files to next level
+    int32_t moved_files = 0;
+    int64_t moved_bytes = 0;
+    for (unsigned int l = 0; l < c->num_input_levels(); l++) {
+      if (c->level(l) == c->output_level()) {
+        continue;
+      }
+      for (size_t i = 0; i < c->num_input_files(l); i++) {
+        FileMetaData* f = c->input(l, i);
+        c->edit()->DeleteFile(c->level(l), f->fd.GetNumber());
+        c->edit()->AddFile(c->output_level(), f->fd.GetNumber(),
+                           f->fd.GetPathId(), f->fd.GetFileSize(), f->smallest,
+                           f->largest, f->fd.smallest_seqno,
+                           f->fd.largest_seqno, f->marked_for_compaction);
+
+        ROCKS_LOG_BUFFER(
+            log_buffer,
+            "[%s] Moving #%" PRIu64 " to level-%d %" PRIu64 " bytes\n",
+            c->column_family_data()->GetName().c_str(), f->fd.GetNumber(),
+            c->output_level(), f->fd.GetFileSize());
+        ++moved_files;
+        moved_bytes += f->fd.GetFileSize();
+      }
+    }
+
+    status = versions_->LogAndApply(c->column_family_data(),
+                                    *c->mutable_cf_options(), c->edit(),
+                                    &mutex_, directories_.GetDbDir());
+    // Use latest MutableCFOptions
+    InstallSuperVersionAndScheduleWork(c->column_family_data(),
+                                       &job_context->superversion_contexts[0],
+                                       *c->mutable_cf_options());
+
+    VersionStorageInfo::LevelSummaryStorage tmp;
+    c->column_family_data()->internal_stats()->IncBytesMoved(c->output_level(),
+                                                             moved_bytes);
+    {
+      event_logger_.LogToBuffer(log_buffer)
+          << "job" << job_context->job_id << "event"
+          << "trivial_move"
+          << "destination_level" << c->output_level() << "files" << moved_files
+          << "total_files_size" << moved_bytes;
+    }
+    ROCKS_LOG_BUFFER(
+        log_buffer,
+        "[%s] Moved #%d files to level-%d %" PRIu64 " bytes %s: %s\n",
+        c->column_family_data()->GetName().c_str(), moved_files,
+        c->output_level(), moved_bytes, status.ToString().c_str(),
+        c->column_family_data()->current()->storage_info()->LevelSummary(&tmp));
+    *made_progress = true;
+
+    // Clear Instrument
+    ThreadStatusUtil::ResetThreadStatus();
+    TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:AfterCompaction",
+                             c->column_family_data());
+  } else if (!is_prepicked && c->output_level() > 0 &&
+             c->output_level() ==
+                 c->column_family_data()
+                     ->current()
+                     ->storage_info()
+                     ->MaxOutputLevel(
+                         immutable_db_options_.allow_ingest_behind) &&
+             env_->GetBackgroundThreads(Env::Priority::BOTTOM) > 0) {
+    // Forward compactions involving last level to the bottom pool if it exists,
+    // such that compactions unlikely to contribute to write stalls can be
+    // delayed or deprioritized.
+    TEST_SYNC_POINT("DBImpl::BackgroundCompaction:ForwardToBottomPriPool");
+    CompactionArg* ca = new CompactionArg;
+    ca->db = this;
+    ca->prepicked_compaction = new PrepickedCompaction;
+    ca->prepicked_compaction->compaction = c.release();
+    ca->prepicked_compaction->manual_compaction_state = nullptr;
+    // Transfer requested token, so it doesn't need to do it again.
+    ca->prepicked_compaction->task_token = std::move(task_token);
+    ++bg_bottom_compaction_scheduled_;
+    env_->Schedule(&DBImpl::BGWorkBottomCompaction, ca, Env::Priority::BOTTOM,
+                   this, &DBImpl::UnscheduleCompactionCallback);
+  } else {
+    TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:BeforeCompaction",
+                             c->column_family_data());
+    int output_level __attribute__((__unused__));
+    output_level = c->output_level();
+    TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:NonTrivial",
+                             &output_level);
+    std::vector<SequenceNumber> snapshot_seqs;
+    SequenceNumber earliest_write_conflict_snapshot;
+    SnapshotChecker* snapshot_checker;
+    GetSnapshotContext(job_context, &snapshot_seqs,
+                       &earliest_write_conflict_snapshot, &snapshot_checker);
+    assert(is_snapshot_supported_ || snapshots_.empty());
+    CompactionJob compaction_job(
+        job_context->job_id, c.get(), immutable_db_options_,
+        env_options_for_compaction_, versions_.get(), &shutting_down_,
+        preserve_deletes_seqnum_.load(), log_buffer, directories_.GetDbDir(),
+        GetDataDir(c->column_family_data(), c->output_path_id()), stats_,
+        &mutex_, &error_handler_, snapshot_seqs,
+        earliest_write_conflict_snapshot, snapshot_checker, table_cache_,
+        &event_logger_, c->mutable_cf_options()->paranoid_file_checks,
+        c->mutable_cf_options()->report_bg_io_stats, dbname_,
+        &compaction_job_stats, thread_pri);
+    compaction_job.Prepare();
+
+    NotifyOnCompactionBegin(c->column_family_data(), c.get(), status,
+                            compaction_job_stats, job_context->job_id);
+
+    mutex_.Unlock();
+    compaction_job.Run();
+    TEST_SYNC_POINT("DBImpl::BackgroundCompaction:NonTrivial:AfterRun");
+    mutex_.Lock();
+
+    status = compaction_job.Install(*c->mutable_cf_options());
+    if (status.ok()) {
+      InstallSuperVersionAndScheduleWork(c->column_family_data(),
+                                         &job_context->superversion_contexts[0],
+                                         *c->mutable_cf_options());
+    }
+    *made_progress = true;
+    TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:AfterCompaction",
+                             c->column_family_data());
+  }
+  if (c != nullptr) {
+    c->ReleaseCompactionFiles(status);
+    *made_progress = true;
+
+#ifndef ROCKSDB_LITE
+    // Need to make sure SstFileManager does its bookkeeping
+    auto sfm = static_cast<SstFileManagerImpl*>(
+        immutable_db_options_.sst_file_manager.get());
+    if (sfm && sfm_reserved_compact_space) {
+      sfm->OnCompactionCompletion(c.get());
+    }
+#endif  // ROCKSDB_LITE
+
+    NotifyOnCompactionCompleted(c->column_family_data(), c.get(), status,
+                                compaction_job_stats, job_context->job_id);
+  }
+
+  if (status.ok() || status.IsCompactionTooLarge()) {
+    // Done
+  } else if (status.IsShutdownInProgress()) {
+    // Ignore compaction errors found during shutting down
+  } else {
+    ROCKS_LOG_WARN(immutable_db_options_.info_log, "Compaction error: %s",
+                   status.ToString().c_str());
+    error_handler_.SetBGError(status, BackgroundErrorReason::kCompaction);
+    if (c != nullptr && !is_manual && !error_handler_.IsBGWorkStopped()) {
+      // Put this cfd back in the compaction queue so we can retry after some
+      // time
+      auto cfd = c->column_family_data();
+      assert(cfd != nullptr);
+      // Since this compaction failed, we need to recompute the score so it
+      // takes the original input files into account
+      c->column_family_data()
+          ->current()
+          ->storage_info()
+          ->ComputeCompactionScore(*(c->immutable_cf_options()),
+                                   *(c->mutable_cf_options()));
+      if (!cfd->queued_for_compaction()) {
+        AddToCompactionQueue(cfd);
+        ++unscheduled_compactions_;
+      }
+    }
+  }
+  // this will unref its input_version and column_family_data
+  c.reset();
+
+  if (is_manual) {
+    ManualCompactionState* m = manual_compaction;
+    if (!status.ok()) {
+      m->status = status;
+      m->done = true;
+    }
+    // For universal compaction:
+    //   Because universal compaction always happens at level 0, so one
+    //   compaction will pick up all overlapped files. No files will be
+    //   filtered out due to size limit and left for a successive compaction.
+    //   So we can safely conclude the current compaction.
+    //
+    //   Also note that, if we don't stop here, then the current compaction
+    //   writes a new file back to level 0, which will be used in successive
+    //   compaction. Hence the manual compaction will never finish.
+    //
+    // Stop the compaction if manual_end points to nullptr -- this means
+    // that we compacted the whole range. manual_end should always point
+    // to nullptr in case of universal compaction
+    if (m->manual_end == nullptr) {
+      m->done = true;
+    }
+    if (!m->done) {
+      // We only compacted part of the requested range.  Update *m
+      // to the range that is left to be compacted.
+      // Universal and FIFO compactions should always compact the whole range
+      assert(m->cfd->ioptions()->compaction_style !=
+                 kCompactionStyleUniversal ||
+             m->cfd->ioptions()->num_levels > 1);
+      assert(m->cfd->ioptions()->compaction_style != kCompactionStyleFIFO);
+      m->tmp_storage = *m->manual_end;
+      m->begin = &m->tmp_storage;
+      m->incomplete = true;
+    }
+    m->in_progress = false;  // not being processed anymore
+  }
+  TEST_SYNC_POINT("DBImpl::BackgroundCompaction:Finish");
+  return status;
+}
+
+bool DBImpl::HasPendingManualCompaction() {
+  return (!manual_compaction_dequeue_.empty());
+}
+
+void DBImpl::AddManualCompaction(DBImpl::ManualCompactionState* m) {
+  manual_compaction_dequeue_.push_back(m);
+}
+
+void DBImpl::RemoveManualCompaction(DBImpl::ManualCompactionState* m) {
+  // Remove from queue
+  std::deque<ManualCompactionState*>::iterator it =
+      manual_compaction_dequeue_.begin();
+  while (it != manual_compaction_dequeue_.end()) {
+    if (m == (*it)) {
+      it = manual_compaction_dequeue_.erase(it);
+      return;
+    }
+    it++;
+  }
+  assert(false);
+  return;
+}
+
+bool DBImpl::ShouldntRunManualCompaction(ManualCompactionState* m) {
+  if (num_running_ingest_file_ > 0) {
+    // We need to wait for other IngestExternalFile() calls to finish
+    // before running a manual compaction.
+    return true;
+  }
+  if (m->exclusive) {
+    return (bg_bottom_compaction_scheduled_ > 0 ||
+            bg_compaction_scheduled_ > 0);
+  }
+  std::deque<ManualCompactionState*>::iterator it =
+      manual_compaction_dequeue_.begin();
+  bool seen = false;
+  while (it != manual_compaction_dequeue_.end()) {
+    if (m == (*it)) {
+      it++;
+      seen = true;
+      continue;
+    } else if (MCOverlap(m, (*it)) && (!seen && !(*it)->in_progress)) {
+      // Consider the other manual compaction *it, conflicts if:
+      // overlaps with m
+      // and (*it) is ahead in the queue and is not yet in progress
+      return true;
+    }
+    it++;
+  }
+  return false;
+}
+
+bool DBImpl::HaveManualCompaction(ColumnFamilyData* cfd) {
+  // Remove from priority queue
+  std::deque<ManualCompactionState*>::iterator it =
+      manual_compaction_dequeue_.begin();
+  while (it != manual_compaction_dequeue_.end()) {
+    if ((*it)->exclusive) {
+      return true;
+    }
+    if ((cfd == (*it)->cfd) && (!((*it)->in_progress || (*it)->done))) {
+      // Allow automatic compaction if manual compaction is
+      // in progress
+      return true;
+    }
+    it++;
+  }
+  return false;
+}
+
+bool DBImpl::HasExclusiveManualCompaction() {
+  // Remove from priority queue
+  std::deque<ManualCompactionState*>::iterator it =
+      manual_compaction_dequeue_.begin();
+  while (it != manual_compaction_dequeue_.end()) {
+    if ((*it)->exclusive) {
+      return true;
+    }
+    it++;
+  }
+  return false;
+}
+
+bool DBImpl::MCOverlap(ManualCompactionState* m, ManualCompactionState* m1) {
+  if ((m->exclusive) || (m1->exclusive)) {
+    return true;
+  }
+  if (m->cfd != m1->cfd) {
+    return false;
+  }
+  return true;
+}
+
+#ifndef ROCKSDB_LITE
+void DBImpl::BuildCompactionJobInfo(
+    const ColumnFamilyData* cfd, Compaction* c, const Status& st,
+    const CompactionJobStats& compaction_job_stats, const int job_id,
+    const Version* current, CompactionJobInfo* compaction_job_info) const {
+  assert(compaction_job_info != nullptr);
+  compaction_job_info->cf_id = cfd->GetID();
+  compaction_job_info->cf_name = cfd->GetName();
+  compaction_job_info->status = st;
+  compaction_job_info->thread_id = env_->GetThreadID();
+  compaction_job_info->job_id = job_id;
+  compaction_job_info->base_input_level = c->start_level();
+  compaction_job_info->output_level = c->output_level();
+  compaction_job_info->stats = compaction_job_stats;
+  compaction_job_info->table_properties = c->GetOutputTableProperties();
+  compaction_job_info->compaction_reason = c->compaction_reason();
+  compaction_job_info->compression = c->output_compression();
+  for (size_t i = 0; i < c->num_input_levels(); ++i) {
+    for (const auto fmd : *c->inputs(i)) {
+      auto fn = TableFileName(c->immutable_cf_options()->cf_paths,
+                              fmd->fd.GetNumber(), fmd->fd.GetPathId());
+      compaction_job_info->input_files.push_back(fn);
+      if (compaction_job_info->table_properties.count(fn) == 0) {
+        std::shared_ptr<const TableProperties> tp;
+        auto s = current->GetTableProperties(&tp, fmd, &fn);
+        if (s.ok()) {
+          compaction_job_info->table_properties[fn] = tp;
+        }
+      }
+    }
+  }
+  for (const auto& newf : c->edit()->GetNewFiles()) {
+    compaction_job_info->output_files.push_back(
+        TableFileName(c->immutable_cf_options()->cf_paths,
+                      newf.second.fd.GetNumber(), newf.second.fd.GetPathId()));
+  }
+}
+#endif
+
+// SuperVersionContext gets created and destructed outside of the lock --
+// we use this conveniently to:
+// * malloc one SuperVersion() outside of the lock -- new_superversion
+// * delete SuperVersion()s outside of the lock -- superversions_to_free
+//
+// However, if InstallSuperVersionAndScheduleWork() gets called twice with the
+// same sv_context, we can't reuse the SuperVersion() that got
+// malloced because
+// first call already used it. In that rare case, we take a hit and create a
+// new SuperVersion() inside of the mutex. We do similar thing
+// for superversion_to_free
+
+void DBImpl::InstallSuperVersionAndScheduleWork(
+    ColumnFamilyData* cfd, SuperVersionContext* sv_context,
+    const MutableCFOptions& mutable_cf_options) {
+  mutex_.AssertHeld();
+
+  // Update max_total_in_memory_state_
+  size_t old_memtable_size = 0;
+  auto* old_sv = cfd->GetSuperVersion();
+  if (old_sv) {
+    old_memtable_size = old_sv->mutable_cf_options.write_buffer_size *
+                        old_sv->mutable_cf_options.max_write_buffer_number;
+  }
+
+  // this branch is unlikely to step in
+  if (UNLIKELY(sv_context->new_superversion == nullptr)) {
+    sv_context->NewSuperVersion();
+  }
+  cfd->InstallSuperVersion(sv_context, &mutex_, mutable_cf_options);
+
+  // There may be a small data race here. The snapshot tricking bottommost
+  // compaction may already be released here. But assuming there will always be
+  // newer snapshot created and released frequently, the compaction will be
+  // triggered soon anyway.
+  bottommost_files_mark_threshold_ = kMaxSequenceNumber;
+  for (auto* my_cfd : *versions_->GetColumnFamilySet()) {
+    bottommost_files_mark_threshold_ = std::min(
+        bottommost_files_mark_threshold_,
+        my_cfd->current()->storage_info()->bottommost_files_mark_threshold());
+  }
+
+  // Whenever we install new SuperVersion, we might need to issue new flushes or
+  // compactions.
+  SchedulePendingCompaction(cfd);
+  MaybeScheduleFlushOrCompaction();
+
+  // Update max_total_in_memory_state_
+  max_total_in_memory_state_ = max_total_in_memory_state_ - old_memtable_size +
+                               mutable_cf_options.write_buffer_size *
+                                   mutable_cf_options.max_write_buffer_number;
+}
+
+// ShouldPurge is called by FindObsoleteFiles when doing a full scan,
+// and db mutex (mutex_) should already be held. This function performs a
+// linear scan of an vector (files_grabbed_for_purge_) in search of a
+// certain element. We expect FindObsoleteFiles with full scan to occur once
+// every 10 hours by default, and the size of the vector is small.
+// Therefore, the cost is affordable even if the mutex is held.
+// Actually, the current implementation of FindObsoleteFiles with
+// full_scan=true can issue I/O requests to obtain list of files in
+// directories, e.g. env_->getChildren while holding db mutex.
+// In the future, if we want to reduce the cost of search, we may try to keep
+// the vector sorted.
+bool DBImpl::ShouldPurge(uint64_t file_number) const {
+  for (auto fn : files_grabbed_for_purge_) {
+    if (file_number == fn) {
+      return false;
+    }
+  }
+  for (const auto& purge_file_info : purge_queue_) {
+    if (purge_file_info.number == file_number) {
+      return false;
+    }
+  }
+  return true;
+}
+
+// MarkAsGrabbedForPurge is called by FindObsoleteFiles, and db mutex
+// (mutex_) should already be held.
+void DBImpl::MarkAsGrabbedForPurge(uint64_t file_number) {
+  files_grabbed_for_purge_.emplace_back(file_number);
+}
+
+void DBImpl::SetSnapshotChecker(SnapshotChecker* snapshot_checker) {
+  InstrumentedMutexLock l(&mutex_);
+  // snapshot_checker_ should only set once. If we need to set it multiple
+  // times, we need to make sure the old one is not deleted while it is still
+  // using by a compaction job.
+  assert(!snapshot_checker_);
+  snapshot_checker_.reset(snapshot_checker);
+}
+
+void DBImpl::GetSnapshotContext(
+    JobContext* job_context, std::vector<SequenceNumber>* snapshot_seqs,
+    SequenceNumber* earliest_write_conflict_snapshot,
+    SnapshotChecker** snapshot_checker_ptr) {
+  mutex_.AssertHeld();
+  assert(job_context != nullptr);
+  assert(snapshot_seqs != nullptr);
+  assert(earliest_write_conflict_snapshot != nullptr);
+  assert(snapshot_checker_ptr != nullptr);
+
+  *snapshot_checker_ptr = snapshot_checker_.get();
+  if (use_custom_gc_ && *snapshot_checker_ptr == nullptr) {
+    *snapshot_checker_ptr = DisableGCSnapshotChecker::Instance();
+  }
+  if (*snapshot_checker_ptr != nullptr) {
+    // If snapshot_checker is used, that means the flush/compaction may
+    // contain values not visible to snapshot taken after
+    // flush/compaction job starts. Take a snapshot and it will appear
+    // in snapshot_seqs and force compaction iterator to consider such
+    // snapshots.
+    const Snapshot* job_snapshot =
+        GetSnapshotImpl(false /*write_conflict_boundary*/, false /*lock*/);
+    job_context->job_snapshot.reset(new ManagedSnapshot(this, job_snapshot));
+  }
+  *snapshot_seqs = snapshots_.GetAll(earliest_write_conflict_snapshot);
+}
+}  // namespace rocksdb