Support delete rate limiting

Summary:
Introduce DeleteScheduler that allow enforcing a rate limit on file deletion
Instead of deleting files immediately, files are moved to trash directory and deleted in a background thread that apply sleep penalty between deletes if needed.

I have updated PurgeObsoleteFiles and PurgeObsoleteWALFiles to use the delete_scheduler instead of env_->DeleteFile

Test Plan:
added delete_scheduler_test
existing unit tests

Reviewers: kradhakrishnan, anthony, rven, yhchiang, sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D43221

HISTORY.md

@@ -6,6 +6,7 @@
 * Add DBOptions::skip_stats_update_on_db_open.  When it is on, DB::Open() will run faster as it skips the random reads required for loading necessary stats from SST files to optimize compaction.
 * RollbackToSavePoint() in WriteBatch/WriteBatchWithIndex
 * Add NewCompactOnDeletionCollectorFactory() in utilities/table_properties_collectors, which allows rocksdb to mark a SST file as need-compaction when it observes at least D deletion entries in any N consecutive entries in that SST file.  Note that this feature depends on an experimental NeedCompact() API --- the result of this API will not persist after DB restart.
+* Add DBOptions::delete_scheduler. Use NewDeleteScheduler() in include/rocksdb/delete_scheduler.h to create a DeleteScheduler that can be shared among multiple RocksDB instances to control the file deletion rate of SST files that exist in the first db_path.
 
 ### Public API Changes
 * Deprecated WriteOptions::timeout_hint_us. We no longer support write timeout. If you really need this option, talk to us and we might consider returning it.

Makefile

@@ -285,6 +285,7 @@ TESTS = \
 	thread_local_test \
 	geodb_test \
 	rate_limiter_test \
+	delete_scheduler_test \
 	options_test \
 	event_logger_test \
 	cuckoo_table_builder_test \
@@ -785,6 +786,9 @@ fault_injection_test: db/fault_injection_test.o $(LIBOBJECTS) $(TESTHARNESS)
 rate_limiter_test: util/rate_limiter_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
+delete_scheduler_test: util/delete_scheduler_test.o $(LIBOBJECTS) $(TESTHARNESS)
+	$(AM_LINK)
+
 filename_test: db/filename_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 

db/db_impl.cc

@@ -54,6 +54,7 @@
 #include "port/likely.h"
 #include "rocksdb/compaction_filter.h"
 #include "rocksdb/db.h"
+#include "rocksdb/delete_scheduler.h"
 #include "rocksdb/env.h"
 #include "rocksdb/merge_operator.h"
 #include "rocksdb/version.h"
@@ -750,7 +751,13 @@ void DBImpl::PurgeObsoleteFiles(const JobContext& state) {
       continue;
     }
 #endif  // !ROCKSDB_LITE
-    auto file_deletion_status = env_->DeleteFile(fname);
+    Status file_deletion_status;
+    if (db_options_.delete_scheduler != nullptr && type == kTableFile &&
+        path_id == 0) {
+      file_deletion_status = db_options_.delete_scheduler->DeleteFile(fname);
+    } else {
+      file_deletion_status = env_->DeleteFile(fname);
+    }
     if (file_deletion_status.ok()) {
       Log(InfoLogLevel::DEBUG_LEVEL, db_options_.info_log,
           "[JOB %d] Delete %s type=%d #%" PRIu64 " -- %s\n", state.job_id,

db/db_test.cc

@@ -35,6 +35,7 @@
 #include "rocksdb/compaction_filter.h"
 #include "rocksdb/convenience.h"
 #include "rocksdb/db.h"
+#include "rocksdb/delete_scheduler.h"
 #include "rocksdb/env.h"
 #include "rocksdb/experimental.h"
 #include "rocksdb/filter_policy.h"
@@ -58,6 +59,7 @@
 #include "utilities/merge_operators.h"
 #include "util/logging.h"
 #include "util/compression.h"
+#include "util/delete_scheduler_impl.h"
 #include "util/mutexlock.h"
 #include "util/rate_limiter.h"
 #include "util/statistics.h"
@@ -8255,6 +8257,145 @@ TEST_F(DBTest, DeletingOldWalAfterDrop) {
   EXPECT_GT(lognum2, lognum1);
 }
 
+TEST_F(DBTest, RateLimitedDelete) {
+  rocksdb::SyncPoint::GetInstance()->LoadDependency({
+      {"DBTest::RateLimitedDelete:1",
+       "DeleteSchedulerImpl::BackgroundEmptyTrash"},
+  });
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+
+  Options options = CurrentOptions();
+  options.disable_auto_compactions = true;
+  env_->no_sleep_ = true;
+  options.env = env_;
+
+  std::string trash_dir = test::TmpDir(env_) + "/trash";
+  int64_t rate_bytes_per_sec = 1024 * 10;  // 10 Kbs / Sec
+  Status s;
+  options.delete_scheduler.reset(NewDeleteScheduler(
+      env_, trash_dir, rate_bytes_per_sec, nullptr, false, &s));
+  ASSERT_OK(s);
+
+  Destroy(last_options_);
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+  ASSERT_OK(TryReopen(options));
+  // Create 4 files in L0
+  for (char v = 'a'; v <= 'd'; v++) {
+    ASSERT_OK(Put("Key2", DummyString(1024, v)));
+    ASSERT_OK(Put("Key3", DummyString(1024, v)));
+    ASSERT_OK(Put("Key4", DummyString(1024, v)));
+    ASSERT_OK(Put("Key1", DummyString(1024, v)));
+    ASSERT_OK(Put("Key4", DummyString(1024, v)));
+    ASSERT_OK(Flush());
+  }
+  // We created 4 sst files in L0
+  ASSERT_EQ("4", FilesPerLevel(0));
+
+  uint64_t total_files_size = 0;
+  std::vector<LiveFileMetaData> metadata;
+  db_->GetLiveFilesMetaData(&metadata);
+  for (const auto& meta : metadata) {
+    total_files_size += meta.size;
+  }
+
+  // Compaction will move the 4 files in L0 to trash and create 1 L1 file
+  ASSERT_OK(db_->CompactRange(CompactRangeOptions(), nullptr, nullptr));
+  ASSERT_EQ("0,1", FilesPerLevel(0));
+
+  // Hold BackgroundEmptyTrash
+  TEST_SYNC_POINT("DBTest::RateLimitedDelete:1");
+
+  uint64_t delete_start_time = env_->NowMicros();
+  reinterpret_cast<DeleteSchedulerImpl*>(options.delete_scheduler.get())
+      ->TEST_WaitForEmptyTrash();
+  uint64_t time_spent_deleting = env_->NowMicros() - delete_start_time;
+  uint64_t expected_delete_time =
+      ((total_files_size * 1000000) / rate_bytes_per_sec);
+  ASSERT_GT(time_spent_deleting, expected_delete_time * 0.9);
+  ASSERT_LT(time_spent_deleting, expected_delete_time * 1.1);
+  printf("Delete time = %" PRIu64 ", Expected delete time = %" PRIu64
+         ", Ratio %f\n",
+         time_spent_deleting, expected_delete_time,
+         static_cast<double>(time_spent_deleting) / expected_delete_time);
+
+  env_->no_sleep_ = false;
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
+// Create a DB with 2 db_paths, and generate multiple files in the 2
+// db_paths using CompactRangeOptions, make sure that files that were
+// deleted from first db_path were deleted using DeleteScheduler and
+// files in the second path were not.
+TEST_F(DBTest, DeleteSchedulerMultipleDBPaths) {
+  int bg_delete_file = 0;
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "DeleteSchedulerImpl::DeleteTrashFile:DeleteFile",
+      [&](void* arg) { bg_delete_file++; });
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  Options options = CurrentOptions();
+  options.disable_auto_compactions = true;
+  options.db_paths.emplace_back(dbname_, 1024 * 100);
+  options.db_paths.emplace_back(dbname_ + "_2", 1024 * 100);
+  env_->no_sleep_ = true;
+  options.env = env_;
+
+  std::string trash_dir = test::TmpDir(env_) + "/trash";
+  int64_t rate_bytes_per_sec = 1024 * 1024;  // 1 Mb / Sec
+  Status s;
+  options.delete_scheduler.reset(NewDeleteScheduler(
+      env_, trash_dir, rate_bytes_per_sec, nullptr, false, &s));
+  ASSERT_OK(s);
+
+  DestroyAndReopen(options);
+
+  // Create 4 files in L0
+  for (int i = 0; i < 4; i++) {
+    ASSERT_OK(Put("Key" + ToString(i), DummyString(1024, 'A')));
+    ASSERT_OK(Flush());
+  }
+  // We created 4 sst files in L0
+  ASSERT_EQ("4", FilesPerLevel(0));
+  // Compaction will delete files from L0 in first db path and generate a new
+  // file in L1 in second db path
+  CompactRangeOptions compact_options;
+  compact_options.target_path_id = 1;
+  Slice begin("Key0");
+  Slice end("Key3");
+  ASSERT_OK(db_->CompactRange(compact_options, &begin, &end));
+  ASSERT_EQ("0,1", FilesPerLevel(0));
+
+  // Create 4 files in L0
+  for (int i = 4; i < 8; i++) {
+    ASSERT_OK(Put("Key" + ToString(i), DummyString(1024, 'B')));
+    ASSERT_OK(Flush());
+  }
+  ASSERT_EQ("4,1", FilesPerLevel(0));
+
+  // Compaction will delete files from L0 in first db path and generate a new
+  // file in L1 in second db path
+  begin = "Key4";
+  end  = "Key7";
+  ASSERT_OK(db_->CompactRange(compact_options, &begin, &end));
+  ASSERT_EQ("0,2", FilesPerLevel(0));
+
+  reinterpret_cast<DeleteSchedulerImpl*>(options.delete_scheduler.get())
+      ->TEST_WaitForEmptyTrash();
+  ASSERT_EQ(bg_delete_file, 8);
+
+  compact_options.bottommost_level_compaction =
+      BottommostLevelCompaction::kForce;
+  ASSERT_OK(db_->CompactRange(compact_options, nullptr, nullptr));
+  ASSERT_EQ("0,1", FilesPerLevel(0));
+
+  reinterpret_cast<DeleteSchedulerImpl*>(options.delete_scheduler.get())
+      ->TEST_WaitForEmptyTrash();
+  ASSERT_EQ(bg_delete_file, 8);
+
+  env_->no_sleep_ = false;
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
 }  // namespace rocksdb
 
 #endif

include/rocksdb/delete_scheduler.h

@@ -0,0 +1,62 @@
+//  Copyright (c) 2015, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+
+#pragma once
+
+#include <map>
+#include <string>
+
+#include "rocksdb/status.h"
+
+namespace rocksdb {
+
+class Env;
+class Logger;
+
+// DeleteScheduler allow the DB to enforce a rate limit on file deletion,
+// Instead of deleteing files immediately, files are moved to trash_dir
+// and deleted in a background thread that apply sleep penlty between deletes
+// if they are happening in a rate faster than rate_bytes_per_sec,
+//
+// Rate limiting can be turned off by setting rate_bytes_per_sec = 0, In this
+// case DeleteScheduler will delete files immediately.
+class DeleteScheduler {
+ public:
+  virtual ~DeleteScheduler() {}
+
+  // Return delete rate limit in bytes per second
+  virtual int64_t GetRateBytesPerSecond() = 0;
+
+  // Move file to trash directory and schedule it's deletion
+  virtual Status DeleteFile(const std::string& fname) = 0;
+
+  // Return a map containing errors that happened in the background thread
+  // file_path => error status
+  virtual std::map<std::string, Status> GetBackgroundErrors() = 0;
+};
+
+// Create a new DeleteScheduler that can be shared among multiple RocksDB
+// instances to control the file deletion rate.
+//
+// @env: Pointer to Env object, please see "rocksdb/env.h".
+// @trash_dir: Path to the directory where deleted files will be moved into
+//    to be deleted in a background thread while applying rate limiting. If this
+//    directory dont exist, it will be created. This directory should not be
+//    used by any other process or any other DeleteScheduler.
+// @rate_bytes_per_sec: How many bytes should be deleted per second, If this
+//    value is set to 1024 (1 Kb / sec) and we deleted a file of size 4 Kb
+//    in 1 second, we will wait for another 3 seconds before we delete other
+//    files, Set to 0 to disable rate limiting.
+// @info_log: If not nullptr, info_log will be used to log errors.
+// @delete_exisitng_trash: If set to true, the newly created DeleteScheduler
+//    will delete files that already exist in trash_dir.
+// @status: If not nullptr, status will contain any errors that happened during
+//    creating the missing trash_dir or deleting existing files in trash.
+extern DeleteScheduler* NewDeleteScheduler(
+    Env* env, const std::string& trash_dir, int64_t rate_bytes_per_sec,
+    std::shared_ptr<Logger> info_log = nullptr,
+    bool delete_exisitng_trash = true, Status* status = nullptr);
+
+}  // namespace rocksdb

include/rocksdb/options.h

@@ -43,6 +43,7 @@ class TableFactory;
 class MemTableRepFactory;
 class TablePropertiesCollectorFactory;
 class RateLimiter;
+class DeleteScheduler;
 class Slice;
 class SliceTransform;
 class Statistics;
@@ -786,6 +787,13 @@ struct DBOptions {
   // Default: nullptr
   std::shared_ptr<RateLimiter> rate_limiter;
 
+  // Use to control files deletion rate, can be used among multiple
+  // RocksDB instances. delete_scheduler is only used to delete table files that
+  // need to be deleted from the first db_path (db_name if db_paths is empty),
+  // other files types and other db_paths wont be affected by delete_scheduler.
+  // Default: nullptr (disabled)
+  std::shared_ptr<DeleteScheduler> delete_scheduler;
+
   // Any internal progress/error information generated by the db will
   // be written to info_log if it is non-nullptr, or to a file stored
   // in the same directory as the DB contents if info_log is nullptr.

src.mk

@@ -83,6 +83,7 @@ LIB_SOURCES =                                                   \
   util/compaction_job_stats_impl.cc                             \
   util/crc32c.cc                                                \
   util/db_info_dumper.cc                                        \
+  util/delete_scheduler_impl.cc                                 \
   util/dynamic_bloom.cc                                         \
   util/env.cc                                                   \
   util/env_hdfs.cc                                              \

util/delete_scheduler_impl.cc

@@ -0,0 +1,228 @@
+//  Copyright (c) 2015, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+
+#include <thread>
+#include <vector>
+
+#include "port/port.h"
+#include "rocksdb/env.h"
+#include "util/delete_scheduler_impl.h"
+#include "util/mutexlock.h"
+#include "util/sync_point.h"
+
+namespace rocksdb {
+
+DeleteSchedulerImpl::DeleteSchedulerImpl(Env* env, const std::string& trash_dir,
+                                         int64_t rate_bytes_per_sec,
+                                         std::shared_ptr<Logger> info_log)
+    : env_(env),
+      trash_dir_(trash_dir),
+      rate_bytes_per_sec_(rate_bytes_per_sec),
+      pending_files_(0),
+      closing_(false),
+      cv_(&mu_),
+      info_log_(info_log) {
+  if (rate_bytes_per_sec_ == 0) {
+    // Rate limiting is disabled
+    bg_thread_.reset();
+  } else {
+    bg_thread_.reset(
+        new std::thread(&DeleteSchedulerImpl::BackgroundEmptyTrash, this));
+  }
+}
+
+DeleteSchedulerImpl::~DeleteSchedulerImpl() {
+  {
+    MutexLock l(&mu_);
+    closing_ = true;
+    cv_.SignalAll();
+  }
+  if (bg_thread_) {
+    bg_thread_->join();
+  }
+}
+
+Status DeleteSchedulerImpl::DeleteFile(const std::string& file_path) {
+  if (rate_bytes_per_sec_ == 0) {
+    // Rate limiting is disabled
+    return env_->DeleteFile(file_path);
+  }
+
+  // Move file to trash
+  std::string path_in_trash;
+  Status s = MoveToTrash(file_path, &path_in_trash);
+  if (!s.ok()) {
+    Log(InfoLogLevel::ERROR_LEVEL, info_log_,
+        "Failed to move %s to trash directory (%s)", file_path.c_str(),
+        trash_dir_.c_str());
+    return env_->DeleteFile(file_path);
+  }
+
+  // Add file to delete queue
+  {
+    MutexLock l(&mu_);
+    queue_.push(path_in_trash);
+    pending_files_++;
+    if (pending_files_ == 1) {
+      cv_.SignalAll();
+    }
+  }
+  return s;
+}
+
+std::map<std::string, Status> DeleteSchedulerImpl::GetBackgroundErrors() {
+  MutexLock l(&mu_);
+  return bg_errors_;
+}
+
+Status DeleteSchedulerImpl::MoveToTrash(const std::string& file_path,
+                                        std::string* path_in_trash) {
+  Status s;
+  // Figure out the name of the file in trash folder
+  size_t idx = file_path.rfind("/");
+  if (idx == std::string::npos || idx == file_path.size() - 1) {
+    return Status::InvalidArgument("file_path is corrupted");
+  }
+  *path_in_trash = trash_dir_ + file_path.substr(idx);
+  std::string unique_suffix = "";
+
+  if (*path_in_trash == file_path) {
+    // This file is already in trash
+    return s;
+  }
+
+  // TODO(tec) : Implement Env::RenameFileIfNotExist and remove
+  //             file_move_mu mutex.
+  MutexLock l(&file_move_mu_);
+  while (true) {
+    s = env_->FileExists(*path_in_trash + unique_suffix);
+    if (s.IsNotFound()) {
+      // We found a path for our file in trash
+      *path_in_trash += unique_suffix;
+      s = env_->RenameFile(file_path, *path_in_trash);
+      break;
+    } else if (s.ok()) {
+      // Name conflict, generate new random suffix
+      unique_suffix = env_->GenerateUniqueId();
+    } else {
+      // Error during FileExists call, we cannot continue
+      break;
+    }
+  }
+  return s;
+}
+
+void DeleteSchedulerImpl::BackgroundEmptyTrash() {
+  TEST_SYNC_POINT("DeleteSchedulerImpl::BackgroundEmptyTrash");
+
+  while (true) {
+    MutexLock l(&mu_);
+    while (queue_.empty() && !closing_) {
+      cv_.Wait();
+    }
+
+    if (closing_) {
+      return;
+    }
+
+    // Delete all files in queue_
+    uint64_t start_time = env_->NowMicros();
+    uint64_t total_deleted_bytes = 0;
+    while (!queue_.empty() && !closing_) {
+      std::string path_in_trash = queue_.front();
+      queue_.pop();
+
+      // We dont need to hold the lock while deleting the file
+      mu_.Unlock();
+      uint64_t deleted_bytes = 0;
+      // Delete file from trash and update total_penlty value
+      Status s = DeleteTrashFile(path_in_trash,  &deleted_bytes);
+      total_deleted_bytes += deleted_bytes;
+      mu_.Lock();
+
+      if (!s.ok()) {
+        bg_errors_[path_in_trash] = s;
+      }
+
+      // Apply penlty if necessary
+      uint64_t total_penlty =
+          ((total_deleted_bytes * kMicrosInSecond) / rate_bytes_per_sec_);
+      while (!closing_ && !cv_.TimedWait(start_time + total_penlty)) {}
+
+      pending_files_--;
+      if (pending_files_ == 0) {
+        // Unblock TEST_WaitForEmptyTrash since there are no more files waiting
+        // to be deleted
+        cv_.SignalAll();
+      }
+    }
+  }
+}
+
+Status DeleteSchedulerImpl::DeleteTrashFile(const std::string& path_in_trash,
+                                            uint64_t* deleted_bytes) {
+  uint64_t file_size;
+  Status s = env_->GetFileSize(path_in_trash, &file_size);
+  if (s.ok()) {
+    TEST_SYNC_POINT("DeleteSchedulerImpl::DeleteTrashFile:DeleteFile");
+    s = env_->DeleteFile(path_in_trash);
+  }
+
+  if (!s.ok()) {
+    // Error while getting file size or while deleting
+    Log(InfoLogLevel::ERROR_LEVEL, info_log_,
+        "Failed to delete %s from trash -- %s", path_in_trash.c_str(),
+        s.ToString().c_str());
+    *deleted_bytes = 0;
+  } else {
+    *deleted_bytes = file_size;
+  }
+
+  return s;
+}
+
+void DeleteSchedulerImpl::TEST_WaitForEmptyTrash() {
+  MutexLock l(&mu_);
+  while (pending_files_ > 0 && !closing_) {
+    cv_.Wait();
+  }
+}
+
+DeleteScheduler* NewDeleteScheduler(Env* env, const std::string& trash_dir,
+                                    int64_t rate_bytes_per_sec,
+                                    std::shared_ptr<Logger> info_log,
+                                    bool delete_exisitng_trash,
+                                    Status* status) {
+  DeleteScheduler* res =
+      new DeleteSchedulerImpl(env, trash_dir, rate_bytes_per_sec, info_log);
+
+  Status s;
+  if (trash_dir != "") {
+    s = env->CreateDirIfMissing(trash_dir);
+    if (s.ok() && delete_exisitng_trash) {
+      std::vector<std::string> files_in_trash;
+      s = env->GetChildren(trash_dir, &files_in_trash);
+      if (s.ok()) {
+        for (const std::string& trash_file : files_in_trash) {
+          if (trash_file == "." || trash_file == "..") {
+            continue;
+          }
+          Status file_delete = res->DeleteFile(trash_dir + "/" + trash_file);
+          if (s.ok() && !file_delete.ok()) {
+            s = file_delete;
+          }
+        }
+      }
+    }
+  }
+
+  if (status) {
+    *status = s;
+  }
+
+  return res;
+}
+
+}  // namespace rocksdb

util/delete_scheduler_impl.h

@@ -0,0 +1,81 @@
+//  Copyright (c) 2015, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+
+#pragma once
+
+#include <map>
+#include <queue>
+#include <string>
+#include <thread>
+
+#include "port/port.h"
+
+#include "rocksdb/delete_scheduler.h"
+#include "rocksdb/status.h"
+
+namespace rocksdb {
+
+class Env;
+class Logger;
+
+class DeleteSchedulerImpl : public DeleteScheduler {
+ public:
+  DeleteSchedulerImpl(Env* env, const std::string& trash_dir,
+                      int64_t rate_bytes_per_sec,
+                      std::shared_ptr<Logger> info_log);
+
+  ~DeleteSchedulerImpl();
+
+  // Return delete rate limit in bytes per second
+  int64_t GetRateBytesPerSecond() { return rate_bytes_per_sec_; }
+
+  // Move file to trash directory and schedule it's deletion
+  Status DeleteFile(const std::string& fname);
+
+  // Wait for all files being deleteing in the background to finish or for
+  // destructor to be called.
+  void TEST_WaitForEmptyTrash();
+
+  // Return a map containing errors that happened in BackgroundEmptyTrash
+  // file_path => error status
+  std::map<std::string, Status> GetBackgroundErrors();
+
+ private:
+  Status MoveToTrash(const std::string& file_path, std::string* path_in_trash);
+
+  Status DeleteTrashFile(const std::string& path_in_trash,
+                         uint64_t* deleted_bytes);
+
+  void BackgroundEmptyTrash();
+
+  Env* env_;
+  // Path to the trash directory
+  std::string trash_dir_;
+  // Maximum number of bytes that should be deleted per second
+  int64_t rate_bytes_per_sec_;
+  // Mutex to protect queue_, pending_files_, bg_errors_, closing_
+  port::Mutex mu_;
+  // Queue of files in trash that need to be deleted
+  std::queue<std::string> queue_;
+  // Number of files in trash that are waiting to be deleted
+  int32_t pending_files_;
+  // Errors that happened in BackgroundEmptyTrash (file_path => error)
+  std::map<std::string, Status> bg_errors_;
+  // Set to true in ~DeleteSchedulerImpl() to force BackgroundEmptyTrash to stop
+  bool closing_;
+  // Condition variable signaled in these conditions
+  //    - pending_files_ value change from 0 => 1
+  //    - pending_files_ value change from 1 => 0
+  //    - closing_ value is set to true
+  port::CondVar cv_;
+  // Background thread running BackgroundEmptyTrash
+  std::unique_ptr<std::thread> bg_thread_;
+  // Mutex to protect threads from file name conflicts
+  port::Mutex file_move_mu_;
+  std::shared_ptr<Logger> info_log_;
+  static const uint64_t kMicrosInSecond = 1000 * 1000LL;
+};
+
+}  // namespace rocksdb

util/delete_scheduler_test.cc

@@ -0,0 +1,439 @@
+//  Copyright (c) 2015, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+
+#ifndef __STDC_FORMAT_MACROS
+#define __STDC_FORMAT_MACROS
+#endif
+
+#include <inttypes.h>
+#include <atomic>
+#include <thread>
+#include <vector>
+
+#include "rocksdb/delete_scheduler.h"
+#include "rocksdb/env.h"
+#include "rocksdb/options.h"
+#include "util/delete_scheduler_impl.h"
+#include "util/string_util.h"
+#include "util/sync_point.h"
+#include "util/testharness.h"
+
+namespace rocksdb {
+
+class DeleteSchedulerTest : public testing::Test {
+ public:
+  DeleteSchedulerTest() : env_(Env::Default()) {
+    dummy_files_dir_ = test::TmpDir(env_) + "/dummy_data_dir";
+    DestroyAndCreateDir(dummy_files_dir_);
+    trash_dir_ = test::TmpDir(env_) + "/trash";
+    DestroyAndCreateDir(trash_dir_);
+  }
+
+  ~DeleteSchedulerTest() {
+    rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+    rocksdb::SyncPoint::GetInstance()->LoadDependency({});
+    rocksdb::SyncPoint::GetInstance()->ClearAllCallBacks();
+    DestroyDir(dummy_files_dir_);
+    if (delete_scheduler_ != nullptr) {
+      delete delete_scheduler_;
+      delete_scheduler_ = nullptr;
+    }
+  }
+
+  void WaitForEmptyTrash() {
+    reinterpret_cast<DeleteSchedulerImpl*>(delete_scheduler_)
+        ->TEST_WaitForEmptyTrash();
+  }
+
+  void DestroyDir(const std::string& dir) {
+    if (env_->FileExists(dir).IsNotFound()) {
+      return;
+    }
+    std::vector<std::string> files_in_dir;
+    EXPECT_OK(env_->GetChildren(dir, &files_in_dir));
+    for (auto& file_in_dir : files_in_dir) {
+      if (file_in_dir == "." || file_in_dir == "..") {
+        continue;
+      }
+      EXPECT_OK(env_->DeleteFile(dir + "/" + file_in_dir));
+    }
+    EXPECT_OK(env_->DeleteDir(dir));
+  }
+
+  void DestroyAndCreateDir(const std::string& dir) {
+    DestroyDir(dir);
+    EXPECT_OK(env_->CreateDir(dir));
+  }
+
+  int CountFilesInDir(const std::string& dir) {
+    std::vector<std::string> files_in_dir;
+    EXPECT_OK(env_->GetChildren(dir, &files_in_dir));
+    // Ignore "." and ".."
+    return static_cast<int>(files_in_dir.size()) - 2;
+  }
+
+  std::string NewDummyFile(const std::string& file_name, uint64_t size = 1024) {
+    std::string file_path = dummy_files_dir_ + "/" + file_name;
+    std::unique_ptr<WritableFile> f;
+    env_->NewWritableFile(file_path, &f, EnvOptions());
+    std::string data(size, 'A');
+    EXPECT_OK(f->Append(data));
+    EXPECT_OK(f->Close());
+    return file_path;
+  }
+
+  Env* env_;
+  std::string dummy_files_dir_;
+  std::string trash_dir_;
+  int64_t rate_bytes_per_sec_;
+  DeleteScheduler* delete_scheduler_;
+};
+
+// Test the basic functionality of DeleteScheduler (Rate Limiting).
+// 1- Create 100 dummy files
+// 2- Delete the 100 dummy files using DeleteScheduler
+// 3- Wait for DeleteScheduler to delete all files in trash
+// 4- Measure time spent in step 2,3 and make sure it matches the expected
+//    time from a rate limited delete
+// 5- Make sure that all created files were completely deleted
+TEST_F(DeleteSchedulerTest, BasicRateLimiting) {
+  int num_files = 100;  // 100 files
+  uint64_t file_size = 1024;  // every file is 1 kb
+  std::vector<uint64_t> delete_kbs_per_sec = {512, 200, 100, 50, 25};
+
+  for (size_t t = 0; t < delete_kbs_per_sec.size(); t++) {
+    DestroyAndCreateDir(dummy_files_dir_);
+    rate_bytes_per_sec_ = delete_kbs_per_sec[t] * 1024;
+    delete_scheduler_ =
+        NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_);
+
+    // Create 100 dummy files, every file is 1 Kb
+    std::vector<std::string> generated_files;
+    uint64_t total_files_size = 0;
+    for (int i = 0; i < num_files; i++) {
+      std::string file_name = "file" + ToString(i) + ".data";
+      generated_files.push_back(NewDummyFile(file_name, file_size));
+      total_files_size += file_size;
+    }
+
+    // Delete dummy files and measure time spent to empty trash
+    uint64_t delete_start_time = env_->NowMicros();
+    for (int i = 0; i < num_files; i++) {
+      ASSERT_OK(delete_scheduler_->DeleteFile(generated_files[i]));
+    }
+    ASSERT_EQ(CountFilesInDir(dummy_files_dir_), 0);
+
+    WaitForEmptyTrash();
+    uint64_t time_spent_deleting = env_->NowMicros() - delete_start_time;
+    uint64_t expected_delete_time =
+        ((total_files_size * 1000000) / rate_bytes_per_sec_);
+    ASSERT_GT(time_spent_deleting, expected_delete_time * 0.9);
+    ASSERT_LT(time_spent_deleting, expected_delete_time * 1.1);
+    printf("Delete time = %" PRIu64 ", Expected delete time = %" PRIu64
+           ", Ratio %f\n",
+           time_spent_deleting, expected_delete_time,
+           static_cast<double>(time_spent_deleting) / expected_delete_time);
+
+    ASSERT_EQ(CountFilesInDir(trash_dir_), 0);
+    auto bg_errors = delete_scheduler_->GetBackgroundErrors();
+    ASSERT_EQ(bg_errors.size(), 0);
+  }
+}
+
+// Same as the BasicRateLimiting test but delete files in multiple threads.
+// 1- Create 100 dummy files
+// 2- Delete the 100 dummy files using DeleteScheduler using 10 threads
+// 3- Wait for DeleteScheduler to delete all files in queue
+// 4- Measure time spent in step 2,3 and make sure it matches the expected
+//    time from a rate limited delete
+// 5- Make sure that all created files were completely deleted
+TEST_F(DeleteSchedulerTest, RateLimitingMultiThreaded) {
+  int thread_cnt = 10;
+  int num_files = 10;  // 10 files per thread
+  uint64_t file_size = 1024;  // every file is 1 kb
+  std::vector<uint64_t> delete_kbs_per_sec = {512, 200, 100, 50, 25};
+
+  for (size_t t = 0; t < delete_kbs_per_sec.size(); t++) {
+    DestroyAndCreateDir(dummy_files_dir_);
+    rate_bytes_per_sec_ = delete_kbs_per_sec[t] * 1024;
+    delete_scheduler_ =
+        NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_);
+
+    // Create 100 dummy files, every file is 1 Kb
+    std::vector<std::string> generated_files;
+    uint64_t total_files_size = 0;
+    for (int i = 0; i < num_files * thread_cnt; i++) {
+      std::string file_name = "file" + ToString(i) + ".data";
+      generated_files.push_back(NewDummyFile(file_name, file_size));
+      total_files_size += file_size;
+    }
+
+    // Delete dummy files using 10 threads and measure time spent to empty trash
+    uint64_t delete_start_time = env_->NowMicros();
+    std::atomic<int> thread_num(0);
+    std::vector<std::thread> threads;
+    for (int i = 0; i < thread_cnt; i++) {
+      threads.emplace_back([&]() {
+        int idx = thread_num.fetch_add(1);
+        int range_start = idx * num_files;
+        int range_end = range_start + num_files;
+        for (int j = range_start; j < range_end; j++){
+          ASSERT_OK(delete_scheduler_->DeleteFile(generated_files[j]));
+        }
+      });
+    }
+
+    for (size_t i = 0; i < threads.size(); i++) {
+      threads[i].join();
+    }
+    ASSERT_EQ(CountFilesInDir(dummy_files_dir_), 0);
+
+    WaitForEmptyTrash();
+    uint64_t time_spent_deleting = env_->NowMicros() - delete_start_time;
+    uint64_t expected_delete_time =
+        ((total_files_size * 1000000) / rate_bytes_per_sec_);
+    ASSERT_GT(time_spent_deleting, expected_delete_time * 0.9);
+    ASSERT_LT(time_spent_deleting, expected_delete_time * 1.1);
+    printf("Delete time = %" PRIu64 ", Expected delete time = %" PRIu64
+           ", Ratio %f\n",
+           time_spent_deleting, expected_delete_time,
+           static_cast<double>(time_spent_deleting) / expected_delete_time);
+
+    ASSERT_EQ(CountFilesInDir(trash_dir_), 0);
+    auto bg_errors = delete_scheduler_->GetBackgroundErrors();
+    ASSERT_EQ(bg_errors.size(), 0);
+  }
+}
+
+// Disable rate limiting by setting rate_bytes_per_sec_ to 0 and make sure
+// that when DeleteScheduler delete a file it delete it immediately and dont
+// move it to trash
+TEST_F(DeleteSchedulerTest, DisableRateLimiting) {
+  int bg_delete_file = 0;
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "DeleteSchedulerImpl::DeleteTrashFile:DeleteFile",
+      [&](void* arg) { bg_delete_file++; });
+
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  delete_scheduler_ = NewDeleteScheduler(env_, "", 0);
+
+  for (int i = 0; i < 10; i++) {
+    // Every file we delete will be deleted immediately
+    std::string dummy_file = NewDummyFile("dummy.data");
+    ASSERT_OK(delete_scheduler_->DeleteFile(dummy_file));
+    ASSERT_TRUE(env_->FileExists(dummy_file).IsNotFound());
+    ASSERT_EQ(CountFilesInDir(dummy_files_dir_), 0);
+    ASSERT_EQ(CountFilesInDir(trash_dir_), 0);
+  }
+
+  ASSERT_EQ(bg_delete_file, 0);
+
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
+// Testing that moving files to trash with the same name is not a problem
+// 1- Create 10 files with the same name "conflict.data"
+// 2- Delete the 10 files using DeleteScheduler
+// 3- Make sure that trash directory contain 10 files ("conflict.data" x 10)
+// --- Hold DeleteSchedulerImpl::BackgroundEmptyTrash ---
+// 4- Make sure that files are deleted from trash
+TEST_F(DeleteSchedulerTest, ConflictNames) {
+  rocksdb::SyncPoint::GetInstance()->LoadDependency({
+      {"DeleteSchedulerTest::ConflictNames:1",
+       "DeleteSchedulerImpl::BackgroundEmptyTrash"},
+  });
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  rate_bytes_per_sec_ = 1024 * 1024;  // 1 Mb/sec
+  delete_scheduler_ = NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_);
+
+  // Create "conflict.data" and move it to trash 10 times
+  for (int i = 0; i < 10; i++) {
+    std::string dummy_file = NewDummyFile("conflict.data");
+    ASSERT_OK(delete_scheduler_->DeleteFile(dummy_file));
+  }
+  ASSERT_EQ(CountFilesInDir(dummy_files_dir_), 0);
+  // 10 files ("conflict.data" x 10) in trash
+  ASSERT_EQ(CountFilesInDir(trash_dir_), 10);
+
+  // Hold BackgroundEmptyTrash
+  TEST_SYNC_POINT("DeleteSchedulerTest::ConflictNames:1");
+  WaitForEmptyTrash();
+  ASSERT_EQ(CountFilesInDir(trash_dir_), 0);
+
+  auto bg_errors = delete_scheduler_->GetBackgroundErrors();
+  ASSERT_EQ(bg_errors.size(), 0);
+
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
+// 1- Create 10 dummy files
+// 2- Delete the 10 files using DeleteScheduler (move them to trsah)
+// 3- Delete the 10 files directly (using env_->DeleteFile)
+// --- Hold DeleteSchedulerImpl::BackgroundEmptyTrash ---
+// 4- Make sure that DeleteScheduler failed to delete the 10 files and
+//    reported 10 background errors
+TEST_F(DeleteSchedulerTest, BackgroundError) {
+  rocksdb::SyncPoint::GetInstance()->LoadDependency({
+      {"DeleteSchedulerTest::BackgroundError:1",
+       "DeleteSchedulerImpl::BackgroundEmptyTrash"},
+  });
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  rate_bytes_per_sec_ = 1024 * 1024;  // 1 Mb/sec
+  delete_scheduler_ = NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_);
+
+  // Generate 10 dummy files and move them to trash
+  for (int i = 0; i < 10; i++) {
+    std::string file_name = "data_" + ToString(i) + ".data";
+    ASSERT_OK(delete_scheduler_->DeleteFile(NewDummyFile(file_name)));
+  }
+  ASSERT_EQ(CountFilesInDir(dummy_files_dir_), 0);
+  ASSERT_EQ(CountFilesInDir(trash_dir_), 10);
+
+  // Delete 10 files from trash, this will cause background errors in
+  // BackgroundEmptyTrash since we already deleted the files it was
+  // goind to delete
+  for (int i = 0; i < 10; i++) {
+    std::string file_name = "data_" + ToString(i) + ".data";
+    ASSERT_OK(env_->DeleteFile(trash_dir_ + "/" + file_name));
+  }
+
+  // Hold BackgroundEmptyTrash
+  TEST_SYNC_POINT("DeleteSchedulerTest::BackgroundError:1");
+  WaitForEmptyTrash();
+  auto bg_errors = delete_scheduler_->GetBackgroundErrors();
+  ASSERT_EQ(bg_errors.size(), 10);
+
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
+// 1- Create 10 files in trash
+// 2- Create a DeleteScheduler with delete_exisitng_trash = true
+// 3- Wait for DeleteScheduler to delete all files in queue
+// 4- Make sure that all files in trash directory were deleted
+TEST_F(DeleteSchedulerTest, TrashWithExistingFiles) {
+  std::vector<std::string> dummy_files;
+  for (int i = 0; i < 10; i++) {
+    std::string file_name = "data_" + ToString(i) + ".data";
+    std::string trash_path = trash_dir_ + "/" + file_name;
+    env_->RenameFile(NewDummyFile(file_name), trash_path);
+  }
+  ASSERT_EQ(CountFilesInDir(trash_dir_), 10);
+
+  Status s;
+  rate_bytes_per_sec_ = 1024 * 1024;  // 1 Mb/sec
+  delete_scheduler_ = NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_,
+                                         nullptr, true, &s);
+  ASSERT_OK(s);
+
+  WaitForEmptyTrash();
+  ASSERT_EQ(CountFilesInDir(trash_dir_), 0);
+
+  auto bg_errors = delete_scheduler_->GetBackgroundErrors();
+  ASSERT_EQ(bg_errors.size(), 0);
+}
+
+// 1- Create 10 dummy files
+// 2- Delete 10 dummy files using DeleteScheduler
+// 3- Wait for DeleteScheduler to delete all files in queue
+// 4- Make sure all files in trash directory were deleted
+// 5- Repeat previous steps 5 times
+TEST_F(DeleteSchedulerTest, StartBGEmptyTrashMultipleTimes) {
+  int bg_delete_file = 0;
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "DeleteSchedulerImpl::DeleteTrashFile:DeleteFile",
+      [&](void* arg) { bg_delete_file++; });
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  rate_bytes_per_sec_ = 1024 * 1024;  // 1 MB / sec
+  delete_scheduler_ = NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_);
+
+  // Move files to trash, wait for empty trash, start again
+  for (int run = 1; run <= 5; run++) {
+    // Generate 10 dummy files and move them to trash
+    for (int i = 0; i < 10; i++) {
+      std::string file_name = "data_" + ToString(i) + ".data";
+      ASSERT_OK(delete_scheduler_->DeleteFile(NewDummyFile(file_name)));
+    }
+    ASSERT_EQ(CountFilesInDir(dummy_files_dir_), 0);
+    WaitForEmptyTrash();
+    ASSERT_EQ(bg_delete_file, 10 * run);
+    ASSERT_EQ(CountFilesInDir(trash_dir_), 0);
+
+    auto bg_errors = delete_scheduler_->GetBackgroundErrors();
+    ASSERT_EQ(bg_errors.size(), 0);
+  }
+
+  ASSERT_EQ(bg_delete_file, 50);
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+}
+
+// 1- Create a DeleteScheduler with very slow rate limit (1 Byte / sec)
+// 2- Delete 100 files using DeleteScheduler
+// 3- Delete the DeleteScheduler (call the destructor while queue is not empty)
+// 4- Make sure that not all files were deleted from trash and that
+//    DeleteScheduler background thread did not delete all files
+TEST_F(DeleteSchedulerTest, DestructorWithNonEmptyQueue) {
+  int bg_delete_file = 0;
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "DeleteSchedulerImpl::DeleteTrashFile:DeleteFile",
+      [&](void* arg) { bg_delete_file++; });
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  rate_bytes_per_sec_ = 1;  // 1 Byte / sec
+  delete_scheduler_ = NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_);
+
+  for (int i = 0; i < 100; i++) {
+    std::string file_name = "data_" + ToString(i) + ".data";
+    ASSERT_OK(delete_scheduler_->DeleteFile(NewDummyFile(file_name)));
+  }
+
+  // Deleting 100 files will need >28 hours to delete
+  // we will delete the DeleteScheduler while delete queue is not empty
+  delete delete_scheduler_;
+  delete_scheduler_ = nullptr;
+
+  ASSERT_LT(bg_delete_file, 100);
+  ASSERT_GT(CountFilesInDir(trash_dir_), 0);
+
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
+// 1- Delete the trash directory
+// 2- Delete 10 files using DeleteScheduler
+// 3- Make sure that the 10 files were deleted immediately since DeleteScheduler
+//    failed to move them to trash directory
+TEST_F(DeleteSchedulerTest, MoveToTrashError) {
+  int bg_delete_file = 0;
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "DeleteSchedulerImpl::DeleteTrashFile:DeleteFile",
+      [&](void* arg) { bg_delete_file++; });
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  rate_bytes_per_sec_ = 1024;  // 1 Kb / sec
+  delete_scheduler_ = NewDeleteScheduler(env_, trash_dir_, rate_bytes_per_sec_);
+
+  // We will delete the trash directory, that mean that DeleteScheduler wont
+  // be able to move files to trash and will delete files them immediately.
+  DestroyDir(trash_dir_);
+  for (int i = 0; i < 10; i++) {
+    std::string file_name = "data_" + ToString(i) + ".data";
+    ASSERT_OK(delete_scheduler_->DeleteFile(NewDummyFile(file_name)));
+  }
+
+  ASSERT_EQ(CountFilesInDir(dummy_files_dir_), 0);
+  ASSERT_EQ(bg_delete_file, 0);
+
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
+}  // namespace rocksdb
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

util/options.cc

@@ -21,6 +21,7 @@
 #include "rocksdb/cache.h"
 #include "rocksdb/compaction_filter.h"
 #include "rocksdb/comparator.h"
+#include "rocksdb/delete_scheduler.h"
 #include "rocksdb/env.h"
 #include "rocksdb/memtablerep.h"
 #include "rocksdb/merge_operator.h"
@@ -199,6 +200,7 @@ DBOptions::DBOptions()
       paranoid_checks(true),
       env(Env::Default()),
       rate_limiter(nullptr),
+      delete_scheduler(nullptr),
       info_log(nullptr),
 #ifdef NDEBUG
       info_log_level(INFO_LEVEL),
@@ -250,6 +252,7 @@ DBOptions::DBOptions(const Options& options)
       paranoid_checks(options.paranoid_checks),
       env(options.env),
       rate_limiter(options.rate_limiter),
+      delete_scheduler(options.delete_scheduler),
       info_log(options.info_log),
       info_log_level(options.info_log_level),
       max_open_files(options.max_open_files),
@@ -360,6 +363,8 @@ void DBOptions::Dump(Logger* log) const {
         use_adaptive_mutex);
     Warn(log, "                            Options.rate_limiter: %p",
         rate_limiter.get());
+    Warn(log, "     Options.delete_scheduler.rate_bytes_per_sec: %" PRIi64,
+         delete_scheduler ? delete_scheduler->GetRateBytesPerSecond() : 0);
     Warn(log, "                          Options.bytes_per_sync: %" PRIu64,
         bytes_per_sync);
     Warn(log, "                      Options.wal_bytes_per_sync: %" PRIu64,