Adding upstream version 18.2.2.upstream/18.2.2

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

1 files changed, 845 insertions, 0 deletions

diff --git a/src/rocksdb/db/column_family.h b/src/rocksdb/db/column_family.h
new file mode 100644
index 000000000..3e6d01d22
--- /dev/null
+++ b/src/rocksdb/db/column_family.h
@@ -0,0 +1,845 @@
+//  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.
+
+#pragma once
+
+#include <atomic>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "cache/cache_reservation_manager.h"
+#include "db/memtable_list.h"
+#include "db/table_cache.h"
+#include "db/table_properties_collector.h"
+#include "db/write_batch_internal.h"
+#include "db/write_controller.h"
+#include "options/cf_options.h"
+#include "rocksdb/compaction_job_stats.h"
+#include "rocksdb/db.h"
+#include "rocksdb/env.h"
+#include "rocksdb/options.h"
+#include "trace_replay/block_cache_tracer.h"
+#include "util/hash_containers.h"
+#include "util/thread_local.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+class Version;
+class VersionSet;
+class VersionStorageInfo;
+class MemTable;
+class MemTableListVersion;
+class CompactionPicker;
+class Compaction;
+class InternalKey;
+class InternalStats;
+class ColumnFamilyData;
+class DBImpl;
+class LogBuffer;
+class InstrumentedMutex;
+class InstrumentedMutexLock;
+struct SuperVersionContext;
+class BlobFileCache;
+class BlobSource;
+
+extern const double kIncSlowdownRatio;
+// This file contains a list of data structures for managing column family
+// level metadata.
+//
+// The basic relationships among classes declared here are illustrated as
+// following:
+//
+//       +----------------------+    +----------------------+   +--------+
+//   +---+ ColumnFamilyHandle 1 | +--+ ColumnFamilyHandle 2 |   | DBImpl |
+//   |   +----------------------+ |  +----------------------+   +----+---+
+//   | +--------------------------+                                  |
+//   | |                               +-----------------------------+
+//   | |                               |
+//   | | +-----------------------------v-------------------------------+
+//   | | |                                                             |
+//   | | |                      ColumnFamilySet                        |
+//   | | |                                                             |
+//   | | +-------------+--------------------------+----------------+---+
+//   | |               |                          |                |
+//   | +-------------------------------------+    |                |
+//   |                 |                     |    |                v
+//   |   +-------------v-------------+ +-----v----v---------+
+//   |   |                           | |                    |
+//   |   |     ColumnFamilyData 1    | | ColumnFamilyData 2 |    ......
+//   |   |                           | |                    |
+//   +--->                           | |                    |
+//       |                 +---------+ |                    |
+//       |                 | MemTable| |                    |
+//       |                 |  List   | |                    |
+//       +--------+---+--+-+----+----+ +--------------------++
+//                |   |  |      |
+//                |   |  |      |
+//                |   |  |      +-----------------------+
+//                |   |  +-----------+                  |
+//                v   +--------+     |                  |
+//       +--------+--------+   |     |                  |
+//       |                 |   |     |       +----------v----------+
+// +---> |SuperVersion 1.a +----------------->                     |
+//       |                 +------+  |       | MemTableListVersion |
+//       +---+-------------+   |  |  |       |                     |
+//           |                 |  |  |       +----+------------+---+
+//           |      current    |  |  |            |            |
+//           |   +-------------+  |  |mem         |            |
+//           |   |                |  |            |            |
+//         +-v---v-------+    +---v--v---+  +-----v----+  +----v-----+
+//         |             |    |          |  |          |  |          |
+//         | Version 1.a |    | memtable |  | memtable |  | memtable |
+//         |             |    |   1.a    |  |   1.b    |  |   1.c    |
+//         +-------------+    |          |  |          |  |          |
+//                            +----------+  +----------+  +----------+
+//
+// DBImpl keeps a ColumnFamilySet, which references to all column families by
+// pointing to respective ColumnFamilyData object of each column family.
+// This is how DBImpl can list and operate on all the column families.
+// ColumnFamilyHandle also points to ColumnFamilyData directly, so that
+// when a user executes a query, it can directly find memtables and Version
+// as well as SuperVersion to the column family, without going through
+// ColumnFamilySet.
+//
+// ColumnFamilySet points to the latest view of the LSM-tree (list of memtables
+// and SST files) indirectly, while ongoing operations may hold references
+// to a current or an out-of-date SuperVersion, which in turn points to a
+// point-in-time view of the LSM-tree. This guarantees the memtables and SST
+// files being operated on will not go away, until the SuperVersion is
+// unreferenced to 0 and destoryed.
+//
+// The following graph illustrates a possible referencing relationships:
+//
+// Column       +--------------+      current       +-----------+
+// Family +---->+              +------------------->+           |
+//  Data        | SuperVersion +----------+         | Version A |
+//              |      3       |   imm    |         |           |
+// Iter2 +----->+              |  +-------v------+  +-----------+
+//              +-----+--------+  | MemtableList +----------------> Empty
+//                    |           |   Version r  |  +-----------+
+//                    |           +--------------+  |           |
+//                    +------------------+   current| Version B |
+//              +--------------+         |   +----->+           |
+//              |              |         |   |      +-----+-----+
+// Compaction +>+ SuperVersion +-------------+            ^
+//    Job       |      2       +------+  |                |current
+//              |              +----+ |  |     mem        |    +------------+
+//              +--------------+    | |  +--------------------->            |
+//                                  | +------------------------> MemTable a |
+//                                  |          mem        |    |            |
+//              +--------------+    |                     |    +------------+
+//              |              +--------------------------+
+//  Iter1 +-----> SuperVersion |    |                          +------------+
+//              |      1       +------------------------------>+            |
+//              |              +-+  |        mem               | MemTable b |
+//              +--------------+ |  |                          |            |
+//                               |  |    +--------------+      +-----^------+
+//                               |  |imm | MemtableList |            |
+//                               |  +--->+   Version s  +------------+
+//                               |       +--------------+
+//                               |       +--------------+
+//                               |       | MemtableList |
+//                               +------>+   Version t  +-------->  Empty
+//                                 imm   +--------------+
+//
+// In this example, even if the current LSM-tree consists of Version A and
+// memtable a, which is also referenced by SuperVersion, two older SuperVersion
+// SuperVersion2 and Superversion1 still exist, and are referenced by a
+// compaction job and an old iterator Iter1, respectively. SuperVersion2
+// contains Version B, memtable a and memtable b; SuperVersion1 contains
+// Version B and memtable b (mutable). As a result, Version B and memtable b
+// are prevented from being destroyed or deleted.
+
+// ColumnFamilyHandleImpl is the class that clients use to access different
+// column families. It has non-trivial destructor, which gets called when client
+// is done using the column family
+class ColumnFamilyHandleImpl : public ColumnFamilyHandle {
+ public:
+  // create while holding the mutex
+  ColumnFamilyHandleImpl(ColumnFamilyData* cfd, DBImpl* db,
+                         InstrumentedMutex* mutex);
+  // destroy without mutex
+  virtual ~ColumnFamilyHandleImpl();
+  virtual ColumnFamilyData* cfd() const { return cfd_; }
+
+  virtual uint32_t GetID() const override;
+  virtual const std::string& GetName() const override;
+  virtual Status GetDescriptor(ColumnFamilyDescriptor* desc) override;
+  virtual const Comparator* GetComparator() const override;
+
+ private:
+  ColumnFamilyData* cfd_;
+  DBImpl* db_;
+  InstrumentedMutex* mutex_;
+};
+
+// Does not ref-count ColumnFamilyData
+// We use this dummy ColumnFamilyHandleImpl because sometimes MemTableInserter
+// calls DBImpl methods. When this happens, MemTableInserter need access to
+// ColumnFamilyHandle (same as the client would need). In that case, we feed
+// MemTableInserter dummy ColumnFamilyHandle and enable it to call DBImpl
+// methods
+class ColumnFamilyHandleInternal : public ColumnFamilyHandleImpl {
+ public:
+  ColumnFamilyHandleInternal()
+      : ColumnFamilyHandleImpl(nullptr, nullptr, nullptr),
+        internal_cfd_(nullptr) {}
+
+  void SetCFD(ColumnFamilyData* _cfd) { internal_cfd_ = _cfd; }
+  virtual ColumnFamilyData* cfd() const override { return internal_cfd_; }
+
+ private:
+  ColumnFamilyData* internal_cfd_;
+};
+
+// holds references to memtable, all immutable memtables and version
+struct SuperVersion {
+  // Accessing members of this class is not thread-safe and requires external
+  // synchronization (ie db mutex held or on write thread).
+  ColumnFamilyData* cfd;
+  MemTable* mem;
+  MemTableListVersion* imm;
+  Version* current;
+  MutableCFOptions mutable_cf_options;
+  // Version number of the current SuperVersion
+  uint64_t version_number;
+  WriteStallCondition write_stall_condition;
+
+  // should be called outside the mutex
+  SuperVersion() = default;
+  ~SuperVersion();
+  SuperVersion* Ref();
+  // If Unref() returns true, Cleanup() should be called with mutex held
+  // before deleting this SuperVersion.
+  bool Unref();
+
+  // call these two methods with db mutex held
+  // Cleanup unrefs mem, imm and current. Also, it stores all memtables
+  // that needs to be deleted in to_delete vector. Unrefing those
+  // objects needs to be done in the mutex
+  void Cleanup();
+  void Init(ColumnFamilyData* new_cfd, MemTable* new_mem,
+            MemTableListVersion* new_imm, Version* new_current);
+
+  // The value of dummy is not actually used. kSVInUse takes its address as a
+  // mark in the thread local storage to indicate the SuperVersion is in use
+  // by thread. This way, the value of kSVInUse is guaranteed to have no
+  // conflict with SuperVersion object address and portable on different
+  // platform.
+  static int dummy;
+  static void* const kSVInUse;
+  static void* const kSVObsolete;
+
+ private:
+  std::atomic<uint32_t> refs;
+  // We need to_delete because during Cleanup(), imm->Unref() returns
+  // all memtables that we need to free through this vector. We then
+  // delete all those memtables outside of mutex, during destruction
+  autovector<MemTable*> to_delete;
+};
+
+extern Status CheckCompressionSupported(const ColumnFamilyOptions& cf_options);
+
+extern Status CheckConcurrentWritesSupported(
+    const ColumnFamilyOptions& cf_options);
+
+extern Status CheckCFPathsSupported(const DBOptions& db_options,
+                                    const ColumnFamilyOptions& cf_options);
+
+extern ColumnFamilyOptions SanitizeOptions(const ImmutableDBOptions& db_options,
+                                           const ColumnFamilyOptions& src);
+// Wrap user defined table properties collector factories `from cf_options`
+// into internal ones in int_tbl_prop_collector_factories. Add a system internal
+// one too.
+extern void GetIntTblPropCollectorFactory(
+    const ImmutableCFOptions& ioptions,
+    IntTblPropCollectorFactories* int_tbl_prop_collector_factories);
+
+class ColumnFamilySet;
+
+// This class keeps all the data that a column family needs.
+// Most methods require DB mutex held, unless otherwise noted
+class ColumnFamilyData {
+ public:
+  ~ColumnFamilyData();
+
+  // thread-safe
+  uint32_t GetID() const { return id_; }
+  // thread-safe
+  const std::string& GetName() const { return name_; }
+
+  // Ref() can only be called from a context where the caller can guarantee
+  // that ColumnFamilyData is alive (while holding a non-zero ref already,
+  // holding a DB mutex, or as the leader in a write batch group).
+  void Ref() { refs_.fetch_add(1); }
+
+  // UnrefAndTryDelete() decreases the reference count and do free if needed,
+  // return true if this is freed else false, UnrefAndTryDelete() can only
+  // be called while holding a DB mutex, or during single-threaded recovery.
+  bool UnrefAndTryDelete();
+
+  // SetDropped() can only be called under following conditions:
+  // 1) Holding a DB mutex,
+  // 2) from single-threaded write thread, AND
+  // 3) from single-threaded VersionSet::LogAndApply()
+  // After dropping column family no other operation on that column family
+  // will be executed. All the files and memory will be, however, kept around
+  // until client drops the column family handle. That way, client can still
+  // access data from dropped column family.
+  // Column family can be dropped and still alive. In that state:
+  // *) Compaction and flush is not executed on the dropped column family.
+  // *) Client can continue reading from column family. Writes will fail unless
+  // WriteOptions::ignore_missing_column_families is true
+  // When the dropped column family is unreferenced, then we:
+  // *) Remove column family from the linked list maintained by ColumnFamilySet
+  // *) delete all memory associated with that column family
+  // *) delete all the files associated with that column family
+  void SetDropped();
+  bool IsDropped() const { return dropped_.load(std::memory_order_relaxed); }
+
+  // thread-safe
+  int NumberLevels() const { return ioptions_.num_levels; }
+
+  void SetLogNumber(uint64_t log_number) { log_number_ = log_number; }
+  uint64_t GetLogNumber() const { return log_number_; }
+
+  void SetFlushReason(FlushReason flush_reason) {
+    flush_reason_ = flush_reason;
+  }
+  FlushReason GetFlushReason() const { return flush_reason_; }
+  // thread-safe
+  const FileOptions* soptions() const;
+  const ImmutableOptions* ioptions() const { return &ioptions_; }
+  // REQUIRES: DB mutex held
+  // This returns the MutableCFOptions used by current SuperVersion
+  // You should use this API to reference MutableCFOptions most of the time.
+  const MutableCFOptions* GetCurrentMutableCFOptions() const {
+    return &(super_version_->mutable_cf_options);
+  }
+  // REQUIRES: DB mutex held
+  // This returns the latest MutableCFOptions, which may be not in effect yet.
+  const MutableCFOptions* GetLatestMutableCFOptions() const {
+    return &mutable_cf_options_;
+  }
+
+  // REQUIRES: DB mutex held
+  // Build ColumnFamiliesOptions with immutable options and latest mutable
+  // options.
+  ColumnFamilyOptions GetLatestCFOptions() const;
+
+  bool is_delete_range_supported() { return is_delete_range_supported_; }
+
+  // Validate CF options against DB options
+  static Status ValidateOptions(const DBOptions& db_options,
+                                const ColumnFamilyOptions& cf_options);
+#ifndef ROCKSDB_LITE
+  // REQUIRES: DB mutex held
+  Status SetOptions(
+      const DBOptions& db_options,
+      const std::unordered_map<std::string, std::string>& options_map);
+#endif  // ROCKSDB_LITE
+
+  InternalStats* internal_stats() { return internal_stats_.get(); }
+
+  MemTableList* imm() { return &imm_; }
+  MemTable* mem() { return mem_; }
+
+  bool IsEmpty() {
+    return mem()->GetFirstSequenceNumber() == 0 && imm()->NumNotFlushed() == 0;
+  }
+
+  Version* current() { return current_; }
+  Version* dummy_versions() { return dummy_versions_; }
+  void SetCurrent(Version* _current);
+  uint64_t GetNumLiveVersions() const;    // REQUIRE: DB mutex held
+  uint64_t GetTotalSstFilesSize() const;  // REQUIRE: DB mutex held
+  uint64_t GetLiveSstFilesSize() const;   // REQUIRE: DB mutex held
+  uint64_t GetTotalBlobFileSize() const;  // REQUIRE: DB mutex held
+  void SetMemtable(MemTable* new_mem) {
+    uint64_t memtable_id = last_memtable_id_.fetch_add(1) + 1;
+    new_mem->SetID(memtable_id);
+    mem_ = new_mem;
+  }
+
+  // calculate the oldest log needed for the durability of this column family
+  uint64_t OldestLogToKeep();
+
+  // See Memtable constructor for explanation of earliest_seq param.
+  MemTable* ConstructNewMemtable(const MutableCFOptions& mutable_cf_options,
+                                 SequenceNumber earliest_seq);
+  void CreateNewMemtable(const MutableCFOptions& mutable_cf_options,
+                         SequenceNumber earliest_seq);
+
+  TableCache* table_cache() const { return table_cache_.get(); }
+  BlobSource* blob_source() const { return blob_source_.get(); }
+
+  // See documentation in compaction_picker.h
+  // REQUIRES: DB mutex held
+  bool NeedsCompaction() const;
+  // REQUIRES: DB mutex held
+  Compaction* PickCompaction(const MutableCFOptions& mutable_options,
+                             const MutableDBOptions& mutable_db_options,
+                             LogBuffer* log_buffer);
+
+  // Check if the passed range overlap with any running compactions.
+  // REQUIRES: DB mutex held
+  bool RangeOverlapWithCompaction(const Slice& smallest_user_key,
+                                  const Slice& largest_user_key,
+                                  int level) const;
+
+  // Check if the passed ranges overlap with any unflushed memtables
+  // (immutable or mutable).
+  //
+  // @param super_version A referenced SuperVersion that will be held for the
+  //    duration of this function.
+  //
+  // Thread-safe
+  Status RangesOverlapWithMemtables(const autovector<Range>& ranges,
+                                    SuperVersion* super_version,
+                                    bool allow_data_in_errors, bool* overlap);
+
+  // A flag to tell a manual compaction is to compact all levels together
+  // instead of a specific level.
+  static const int kCompactAllLevels;
+  // A flag to tell a manual compaction's output is base level.
+  static const int kCompactToBaseLevel;
+  // REQUIRES: DB mutex held
+  Compaction* CompactRange(const MutableCFOptions& mutable_cf_options,
+                           const MutableDBOptions& mutable_db_options,
+                           int input_level, int output_level,
+                           const CompactRangeOptions& compact_range_options,
+                           const InternalKey* begin, const InternalKey* end,
+                           InternalKey** compaction_end, bool* manual_conflict,
+                           uint64_t max_file_num_to_ignore,
+                           const std::string& trim_ts);
+
+  CompactionPicker* compaction_picker() { return compaction_picker_.get(); }
+  // thread-safe
+  const Comparator* user_comparator() const {
+    return internal_comparator_.user_comparator();
+  }
+  // thread-safe
+  const InternalKeyComparator& internal_comparator() const {
+    return internal_comparator_;
+  }
+
+  const IntTblPropCollectorFactories* int_tbl_prop_collector_factories() const {
+    return &int_tbl_prop_collector_factories_;
+  }
+
+  SuperVersion* GetSuperVersion() { return super_version_; }
+  // thread-safe
+  // Return a already referenced SuperVersion to be used safely.
+  SuperVersion* GetReferencedSuperVersion(DBImpl* db);
+  // thread-safe
+  // Get SuperVersion stored in thread local storage. If it does not exist,
+  // get a reference from a current SuperVersion.
+  SuperVersion* GetThreadLocalSuperVersion(DBImpl* db);
+  // Try to return SuperVersion back to thread local storage. Return true on
+  // success and false on failure. It fails when the thread local storage
+  // contains anything other than SuperVersion::kSVInUse flag.
+  bool ReturnThreadLocalSuperVersion(SuperVersion* sv);
+  // thread-safe
+  uint64_t GetSuperVersionNumber() const {
+    return super_version_number_.load();
+  }
+  // will return a pointer to SuperVersion* if previous SuperVersion
+  // if its reference count is zero and needs deletion or nullptr if not
+  // As argument takes a pointer to allocated SuperVersion to enable
+  // the clients to allocate SuperVersion outside of mutex.
+  // IMPORTANT: Only call this from DBImpl::InstallSuperVersion()
+  void InstallSuperVersion(SuperVersionContext* sv_context,
+                           const MutableCFOptions& mutable_cf_options);
+  void InstallSuperVersion(SuperVersionContext* sv_context,
+                           InstrumentedMutex* db_mutex);
+
+  void ResetThreadLocalSuperVersions();
+
+  // Protected by DB mutex
+  void set_queued_for_flush(bool value) { queued_for_flush_ = value; }
+  void set_queued_for_compaction(bool value) { queued_for_compaction_ = value; }
+  bool queued_for_flush() { return queued_for_flush_; }
+  bool queued_for_compaction() { return queued_for_compaction_; }
+
+  enum class WriteStallCause {
+    kNone,
+    kMemtableLimit,
+    kL0FileCountLimit,
+    kPendingCompactionBytes,
+  };
+  static std::pair<WriteStallCondition, WriteStallCause>
+  GetWriteStallConditionAndCause(
+      int num_unflushed_memtables, int num_l0_files,
+      uint64_t num_compaction_needed_bytes,
+      const MutableCFOptions& mutable_cf_options,
+      const ImmutableCFOptions& immutable_cf_options);
+
+  // Recalculate some stall conditions, which are changed only during
+  // compaction, adding new memtable and/or recalculation of compaction score.
+  WriteStallCondition RecalculateWriteStallConditions(
+      const MutableCFOptions& mutable_cf_options);
+
+  void set_initialized() { initialized_.store(true); }
+
+  bool initialized() const { return initialized_.load(); }
+
+  const ColumnFamilyOptions& initial_cf_options() {
+    return initial_cf_options_;
+  }
+
+  Env::WriteLifeTimeHint CalculateSSTWriteHint(int level);
+
+  // created_dirs remembers directory created, so that we don't need to call
+  // the same data creation operation again.
+  Status AddDirectories(
+      std::map<std::string, std::shared_ptr<FSDirectory>>* created_dirs);
+
+  FSDirectory* GetDataDir(size_t path_id) const;
+
+  // full_history_ts_low_ can only increase.
+  void SetFullHistoryTsLow(std::string ts_low) {
+    assert(!ts_low.empty());
+    const Comparator* ucmp = user_comparator();
+    assert(ucmp);
+    if (full_history_ts_low_.empty() ||
+        ucmp->CompareTimestamp(ts_low, full_history_ts_low_) > 0) {
+      full_history_ts_low_ = std::move(ts_low);
+    }
+  }
+
+  const std::string& GetFullHistoryTsLow() const {
+    return full_history_ts_low_;
+  }
+
+  ThreadLocalPtr* TEST_GetLocalSV() { return local_sv_.get(); }
+  WriteBufferManager* write_buffer_mgr() { return write_buffer_manager_; }
+  std::shared_ptr<CacheReservationManager>
+  GetFileMetadataCacheReservationManager() {
+    return file_metadata_cache_res_mgr_;
+  }
+
+  SequenceNumber GetFirstMemtableSequenceNumber() const;
+
+  static const uint32_t kDummyColumnFamilyDataId;
+
+  // Keep track of whether the mempurge feature was ever used.
+  void SetMempurgeUsed() { mempurge_used_ = true; }
+  bool GetMempurgeUsed() { return mempurge_used_; }
+
+ private:
+  friend class ColumnFamilySet;
+  ColumnFamilyData(uint32_t id, const std::string& name,
+                   Version* dummy_versions, Cache* table_cache,
+                   WriteBufferManager* write_buffer_manager,
+                   const ColumnFamilyOptions& options,
+                   const ImmutableDBOptions& db_options,
+                   const FileOptions* file_options,
+                   ColumnFamilySet* column_family_set,
+                   BlockCacheTracer* const block_cache_tracer,
+                   const std::shared_ptr<IOTracer>& io_tracer,
+                   const std::string& db_id, const std::string& db_session_id);
+
+  std::vector<std::string> GetDbPaths() const;
+
+  uint32_t id_;
+  const std::string name_;
+  Version* dummy_versions_;  // Head of circular doubly-linked list of versions.
+  Version* current_;         // == dummy_versions->prev_
+
+  std::atomic<int> refs_;  // outstanding references to ColumnFamilyData
+  std::atomic<bool> initialized_;
+  std::atomic<bool> dropped_;  // true if client dropped it
+
+  const InternalKeyComparator internal_comparator_;
+  IntTblPropCollectorFactories int_tbl_prop_collector_factories_;
+
+  const ColumnFamilyOptions initial_cf_options_;
+  const ImmutableOptions ioptions_;
+  MutableCFOptions mutable_cf_options_;
+
+  const bool is_delete_range_supported_;
+
+  std::unique_ptr<TableCache> table_cache_;
+  std::unique_ptr<BlobFileCache> blob_file_cache_;
+  std::unique_ptr<BlobSource> blob_source_;
+
+  std::unique_ptr<InternalStats> internal_stats_;
+
+  WriteBufferManager* write_buffer_manager_;
+
+  MemTable* mem_;
+  MemTableList imm_;
+  SuperVersion* super_version_;
+
+  // An ordinal representing the current SuperVersion. Updated by
+  // InstallSuperVersion(), i.e. incremented every time super_version_
+  // changes.
+  std::atomic<uint64_t> super_version_number_;
+
+  // Thread's local copy of SuperVersion pointer
+  // This needs to be destructed before mutex_
+  std::unique_ptr<ThreadLocalPtr> local_sv_;
+
+  // pointers for a circular linked list. we use it to support iterations over
+  // all column families that are alive (note: dropped column families can also
+  // be alive as long as client holds a reference)
+  ColumnFamilyData* next_;
+  ColumnFamilyData* prev_;
+
+  // This is the earliest log file number that contains data from this
+  // Column Family. All earlier log files must be ignored and not
+  // recovered from
+  uint64_t log_number_;
+
+  std::atomic<FlushReason> flush_reason_;
+
+  // An object that keeps all the compaction stats
+  // and picks the next compaction
+  std::unique_ptr<CompactionPicker> compaction_picker_;
+
+  ColumnFamilySet* column_family_set_;
+
+  std::unique_ptr<WriteControllerToken> write_controller_token_;
+
+  // If true --> this ColumnFamily is currently present in DBImpl::flush_queue_
+  bool queued_for_flush_;
+
+  // If true --> this ColumnFamily is currently present in
+  // DBImpl::compaction_queue_
+  bool queued_for_compaction_;
+
+  uint64_t prev_compaction_needed_bytes_;
+
+  // if the database was opened with 2pc enabled
+  bool allow_2pc_;
+
+  // Memtable id to track flush.
+  std::atomic<uint64_t> last_memtable_id_;
+
+  // Directories corresponding to cf_paths.
+  std::vector<std::shared_ptr<FSDirectory>> data_dirs_;
+
+  bool db_paths_registered_;
+
+  std::string full_history_ts_low_;
+
+  // For charging memory usage of file metadata created for newly added files to
+  // a Version associated with this CFD
+  std::shared_ptr<CacheReservationManager> file_metadata_cache_res_mgr_;
+  bool mempurge_used_;
+};
+
+// ColumnFamilySet has interesting thread-safety requirements
+// * CreateColumnFamily() or RemoveColumnFamily() -- need to be protected by DB
+// mutex AND executed in the write thread.
+// CreateColumnFamily() should ONLY be called from VersionSet::LogAndApply() AND
+// single-threaded write thread. It is also called during Recovery and in
+// DumpManifest().
+// RemoveColumnFamily() is only called from SetDropped(). DB mutex needs to be
+// held and it needs to be executed from the write thread. SetDropped() also
+// guarantees that it will be called only from single-threaded LogAndApply(),
+// but this condition is not that important.
+// * Iteration -- hold DB mutex. If you want to release the DB mutex in the
+// body of the iteration, wrap in a RefedColumnFamilySet.
+// * GetDefault() -- thread safe
+// * GetColumnFamily() -- either inside of DB mutex or from a write thread
+// * GetNextColumnFamilyID(), GetMaxColumnFamily(), UpdateMaxColumnFamily(),
+// NumberOfColumnFamilies -- inside of DB mutex
+class ColumnFamilySet {
+ public:
+  // ColumnFamilySet supports iteration
+  class iterator {
+   public:
+    explicit iterator(ColumnFamilyData* cfd) : current_(cfd) {}
+    // NOTE: minimum operators for for-loop iteration
+    iterator& operator++() {
+      current_ = current_->next_;
+      return *this;
+    }
+    bool operator!=(const iterator& other) const {
+      return this->current_ != other.current_;
+    }
+    ColumnFamilyData* operator*() { return current_; }
+
+   private:
+    ColumnFamilyData* current_;
+  };
+
+  ColumnFamilySet(const std::string& dbname,
+                  const ImmutableDBOptions* db_options,
+                  const FileOptions& file_options, Cache* table_cache,
+                  WriteBufferManager* _write_buffer_manager,
+                  WriteController* _write_controller,
+                  BlockCacheTracer* const block_cache_tracer,
+                  const std::shared_ptr<IOTracer>& io_tracer,
+                  const std::string& db_id, const std::string& db_session_id);
+  ~ColumnFamilySet();
+
+  ColumnFamilyData* GetDefault() const;
+  // GetColumnFamily() calls return nullptr if column family is not found
+  ColumnFamilyData* GetColumnFamily(uint32_t id) const;
+  ColumnFamilyData* GetColumnFamily(const std::string& name) const;
+  // this call will return the next available column family ID. it guarantees
+  // that there is no column family with id greater than or equal to the
+  // returned value in the current running instance or anytime in RocksDB
+  // instance history.
+  uint32_t GetNextColumnFamilyID();
+  uint32_t GetMaxColumnFamily();
+  void UpdateMaxColumnFamily(uint32_t new_max_column_family);
+  size_t NumberOfColumnFamilies() const;
+
+  ColumnFamilyData* CreateColumnFamily(const std::string& name, uint32_t id,
+                                       Version* dummy_version,
+                                       const ColumnFamilyOptions& options);
+
+  iterator begin() { return iterator(dummy_cfd_->next_); }
+  iterator end() { return iterator(dummy_cfd_); }
+
+  Cache* get_table_cache() { return table_cache_; }
+
+  WriteBufferManager* write_buffer_manager() { return write_buffer_manager_; }
+
+  WriteController* write_controller() { return write_controller_; }
+
+ private:
+  friend class ColumnFamilyData;
+  // helper function that gets called from cfd destructor
+  // REQUIRES: DB mutex held
+  void RemoveColumnFamily(ColumnFamilyData* cfd);
+
+  // column_families_ and column_family_data_ need to be protected:
+  // * when mutating both conditions have to be satisfied:
+  // 1. DB mutex locked
+  // 2. thread currently in single-threaded write thread
+  // * when reading, at least one condition needs to be satisfied:
+  // 1. DB mutex locked
+  // 2. accessed from a single-threaded write thread
+  UnorderedMap<std::string, uint32_t> column_families_;
+  UnorderedMap<uint32_t, ColumnFamilyData*> column_family_data_;
+
+  uint32_t max_column_family_;
+  const FileOptions file_options_;
+
+  ColumnFamilyData* dummy_cfd_;
+  // We don't hold the refcount here, since default column family always exists
+  // We are also not responsible for cleaning up default_cfd_cache_. This is
+  // just a cache that makes common case (accessing default column family)
+  // faster
+  ColumnFamilyData* default_cfd_cache_;
+
+  const std::string db_name_;
+  const ImmutableDBOptions* const db_options_;
+  Cache* table_cache_;
+  WriteBufferManager* write_buffer_manager_;
+  WriteController* write_controller_;
+  BlockCacheTracer* const block_cache_tracer_;
+  std::shared_ptr<IOTracer> io_tracer_;
+  const std::string& db_id_;
+  std::string db_session_id_;
+};
+
+// A wrapper for ColumnFamilySet that supports releasing DB mutex during each
+// iteration over the iterator, because the cfd is Refed and Unrefed during
+// each iteration to prevent concurrent CF drop from destroying it (until
+// Unref).
+class RefedColumnFamilySet {
+ public:
+  explicit RefedColumnFamilySet(ColumnFamilySet* cfs) : wrapped_(cfs) {}
+
+  class iterator {
+   public:
+    explicit iterator(ColumnFamilySet::iterator wrapped) : wrapped_(wrapped) {
+      MaybeRef(*wrapped_);
+    }
+    ~iterator() { MaybeUnref(*wrapped_); }
+    inline void MaybeRef(ColumnFamilyData* cfd) {
+      if (cfd->GetID() != ColumnFamilyData::kDummyColumnFamilyDataId) {
+        cfd->Ref();
+      }
+    }
+    inline void MaybeUnref(ColumnFamilyData* cfd) {
+      if (cfd->GetID() != ColumnFamilyData::kDummyColumnFamilyDataId) {
+        cfd->UnrefAndTryDelete();
+      }
+    }
+    // NOTE: minimum operators for for-loop iteration
+    inline iterator& operator++() {
+      ColumnFamilyData* old = *wrapped_;
+      ++wrapped_;
+      // Can only unref & potentially free cfd after accessing its next_
+      MaybeUnref(old);
+      MaybeRef(*wrapped_);
+      return *this;
+    }
+    inline bool operator!=(const iterator& other) const {
+      return this->wrapped_ != other.wrapped_;
+    }
+    inline ColumnFamilyData* operator*() { return *wrapped_; }
+
+   private:
+    ColumnFamilySet::iterator wrapped_;
+  };
+
+  iterator begin() { return iterator(wrapped_->begin()); }
+  iterator end() { return iterator(wrapped_->end()); }
+
+ private:
+  ColumnFamilySet* wrapped_;
+};
+
+// We use ColumnFamilyMemTablesImpl to provide WriteBatch a way to access
+// memtables of different column families (specified by ID in the write batch)
+class ColumnFamilyMemTablesImpl : public ColumnFamilyMemTables {
+ public:
+  explicit ColumnFamilyMemTablesImpl(ColumnFamilySet* column_family_set)
+      : column_family_set_(column_family_set), current_(nullptr) {}
+
+  // Constructs a ColumnFamilyMemTablesImpl equivalent to one constructed
+  // with the arguments used to construct *orig.
+  explicit ColumnFamilyMemTablesImpl(ColumnFamilyMemTablesImpl* orig)
+      : column_family_set_(orig->column_family_set_), current_(nullptr) {}
+
+  // sets current_ to ColumnFamilyData with column_family_id
+  // returns false if column family doesn't exist
+  // REQUIRES: use this function of DBImpl::column_family_memtables_ should be
+  //           under a DB mutex OR from a write thread
+  bool Seek(uint32_t column_family_id) override;
+
+  // Returns log number of the selected column family
+  // REQUIRES: under a DB mutex OR from a write thread
+  uint64_t GetLogNumber() const override;
+
+  // REQUIRES: Seek() called first
+  // REQUIRES: use this function of DBImpl::column_family_memtables_ should be
+  //           under a DB mutex OR from a write thread
+  virtual MemTable* GetMemTable() const override;
+
+  // Returns column family handle for the selected column family
+  // REQUIRES: use this function of DBImpl::column_family_memtables_ should be
+  //           under a DB mutex OR from a write thread
+  virtual ColumnFamilyHandle* GetColumnFamilyHandle() override;
+
+  // Cannot be called while another thread is calling Seek().
+  // REQUIRES: use this function of DBImpl::column_family_memtables_ should be
+  //           under a DB mutex OR from a write thread
+  virtual ColumnFamilyData* current() override { return current_; }
+
+ private:
+  ColumnFamilySet* column_family_set_;
+  ColumnFamilyData* current_;
+  ColumnFamilyHandleInternal handle_;
+};
+
+extern uint32_t GetColumnFamilyID(ColumnFamilyHandle* column_family);
+
+extern const Comparator* GetColumnFamilyUserComparator(
+    ColumnFamilyHandle* column_family);
+
+}  // namespace ROCKSDB_NAMESPACE