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diff --git a/src/rocksdb/db/dbformat.h b/src/rocksdb/db/dbformat.h
new file mode 100644
index 000000000..de98be8df
--- /dev/null
+++ b/src/rocksdb/db/dbformat.h
@@ -0,0 +1,671 @@
+//  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 <stdio.h>
+#include <memory>
+#include <string>
+#include <utility>
+#include "db/lookup_key.h"
+#include "db/merge_context.h"
+#include "logging/logging.h"
+#include "monitoring/perf_context_imp.h"
+#include "rocksdb/comparator.h"
+#include "rocksdb/db.h"
+#include "rocksdb/filter_policy.h"
+#include "rocksdb/slice.h"
+#include "rocksdb/slice_transform.h"
+#include "rocksdb/table.h"
+#include "rocksdb/types.h"
+#include "util/coding.h"
+#include "util/user_comparator_wrapper.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+// The file declares data structures and functions that deal with internal
+// keys.
+// Each internal key contains a user key, a sequence number (SequenceNumber)
+// and a type (ValueType), and they are usually encoded together.
+// There are some related helper classes here.
+
+class InternalKey;
+
+// Value types encoded as the last component of internal keys.
+// DO NOT CHANGE THESE ENUM VALUES: they are embedded in the on-disk
+// data structures.
+// The highest bit of the value type needs to be reserved to SST tables
+// for them to do more flexible encoding.
+enum ValueType : unsigned char {
+  kTypeDeletion = 0x0,
+  kTypeValue = 0x1,
+  kTypeMerge = 0x2,
+  kTypeLogData = 0x3,               // WAL only.
+  kTypeColumnFamilyDeletion = 0x4,  // WAL only.
+  kTypeColumnFamilyValue = 0x5,     // WAL only.
+  kTypeColumnFamilyMerge = 0x6,     // WAL only.
+  kTypeSingleDeletion = 0x7,
+  kTypeColumnFamilySingleDeletion = 0x8,  // WAL only.
+  kTypeBeginPrepareXID = 0x9,             // WAL only.
+  kTypeEndPrepareXID = 0xA,               // WAL only.
+  kTypeCommitXID = 0xB,                   // WAL only.
+  kTypeRollbackXID = 0xC,                 // WAL only.
+  kTypeNoop = 0xD,                        // WAL only.
+  kTypeColumnFamilyRangeDeletion = 0xE,   // WAL only.
+  kTypeRangeDeletion = 0xF,               // meta block
+  kTypeColumnFamilyBlobIndex = 0x10,      // Blob DB only
+  kTypeBlobIndex = 0x11,                  // Blob DB only
+  // When the prepared record is also persisted in db, we use a different
+  // record. This is to ensure that the WAL that is generated by a WritePolicy
+  // is not mistakenly read by another, which would result into data
+  // inconsistency.
+  kTypeBeginPersistedPrepareXID = 0x12,  // WAL only.
+  // Similar to kTypeBeginPersistedPrepareXID, this is to ensure that WAL
+  // generated by WriteUnprepared write policy is not mistakenly read by
+  // another.
+  kTypeBeginUnprepareXID = 0x13,  // WAL only.
+  kMaxValue = 0x7F                // Not used for storing records.
+};
+
+// Defined in dbformat.cc
+extern const ValueType kValueTypeForSeek;
+extern const ValueType kValueTypeForSeekForPrev;
+
+// Checks whether a type is an inline value type
+// (i.e. a type used in memtable skiplist and sst file datablock).
+inline bool IsValueType(ValueType t) {
+  return t <= kTypeMerge || t == kTypeSingleDeletion || t == kTypeBlobIndex;
+}
+
+// Checks whether a type is from user operation
+// kTypeRangeDeletion is in meta block so this API is separated from above
+inline bool IsExtendedValueType(ValueType t) {
+  return IsValueType(t) || t == kTypeRangeDeletion;
+}
+
+// We leave eight bits empty at the bottom so a type and sequence#
+// can be packed together into 64-bits.
+static const SequenceNumber kMaxSequenceNumber = ((0x1ull << 56) - 1);
+
+static const SequenceNumber kDisableGlobalSequenceNumber = port::kMaxUint64;
+
+// The data structure that represents an internal key in the way that user_key,
+// sequence number and type are stored in separated forms.
+struct ParsedInternalKey {
+  Slice user_key;
+  SequenceNumber sequence;
+  ValueType type;
+
+  ParsedInternalKey()
+      : sequence(kMaxSequenceNumber)  // Make code analyzer happy
+  {}  // Intentionally left uninitialized (for speed)
+  ParsedInternalKey(const Slice& u, const SequenceNumber& seq, ValueType t)
+      : user_key(u), sequence(seq), type(t) {}
+  std::string DebugString(bool hex = false) const;
+
+  void clear() {
+    user_key.clear();
+    sequence = 0;
+    type = kTypeDeletion;
+  }
+};
+
+// Return the length of the encoding of "key".
+inline size_t InternalKeyEncodingLength(const ParsedInternalKey& key) {
+  return key.user_key.size() + 8;
+}
+
+// Pack a sequence number and a ValueType into a uint64_t
+extern uint64_t PackSequenceAndType(uint64_t seq, ValueType t);
+
+// Given the result of PackSequenceAndType, store the sequence number in *seq
+// and the ValueType in *t.
+extern void UnPackSequenceAndType(uint64_t packed, uint64_t* seq, ValueType* t);
+
+EntryType GetEntryType(ValueType value_type);
+
+// Append the serialization of "key" to *result.
+extern void AppendInternalKey(std::string* result,
+                              const ParsedInternalKey& key);
+// Serialized internal key consists of user key followed by footer.
+// This function appends the footer to *result, assuming that *result already
+// contains the user key at the end.
+extern void AppendInternalKeyFooter(std::string* result, SequenceNumber s,
+                                    ValueType t);
+
+// Attempt to parse an internal key from "internal_key".  On success,
+// stores the parsed data in "*result", and returns true.
+//
+// On error, returns false, leaves "*result" in an undefined state.
+extern bool ParseInternalKey(const Slice& internal_key,
+                             ParsedInternalKey* result);
+
+// Returns the user key portion of an internal key.
+inline Slice ExtractUserKey(const Slice& internal_key) {
+  assert(internal_key.size() >= 8);
+  return Slice(internal_key.data(), internal_key.size() - 8);
+}
+
+inline Slice ExtractUserKeyAndStripTimestamp(const Slice& internal_key,
+                                             size_t ts_sz) {
+  assert(internal_key.size() >= 8 + ts_sz);
+  return Slice(internal_key.data(), internal_key.size() - 8 - ts_sz);
+}
+
+inline Slice StripTimestampFromUserKey(const Slice& user_key, size_t ts_sz) {
+  assert(user_key.size() >= ts_sz);
+  return Slice(user_key.data(), user_key.size() - ts_sz);
+}
+
+inline uint64_t ExtractInternalKeyFooter(const Slice& internal_key) {
+  assert(internal_key.size() >= 8);
+  const size_t n = internal_key.size();
+  return DecodeFixed64(internal_key.data() + n - 8);
+}
+
+inline ValueType ExtractValueType(const Slice& internal_key) {
+  uint64_t num = ExtractInternalKeyFooter(internal_key);
+  unsigned char c = num & 0xff;
+  return static_cast<ValueType>(c);
+}
+
+// A comparator for internal keys that uses a specified comparator for
+// the user key portion and breaks ties by decreasing sequence number.
+class InternalKeyComparator
+#ifdef NDEBUG
+    final
+#endif
+    : public Comparator {
+ private:
+  UserComparatorWrapper user_comparator_;
+  std::string name_;
+
+ public:
+  explicit InternalKeyComparator(const Comparator* c)
+      : user_comparator_(c),
+        name_("rocksdb.InternalKeyComparator:" +
+              std::string(user_comparator_.Name())) {}
+  virtual ~InternalKeyComparator() {}
+
+  virtual const char* Name() const override;
+  virtual int Compare(const Slice& a, const Slice& b) const override;
+  // Same as Compare except that it excludes the value type from comparison
+  virtual int CompareKeySeq(const Slice& a, const Slice& b) const;
+  virtual void FindShortestSeparator(std::string* start,
+                                     const Slice& limit) const override;
+  virtual void FindShortSuccessor(std::string* key) const override;
+
+  const Comparator* user_comparator() const {
+    return user_comparator_.user_comparator();
+  }
+
+  int Compare(const InternalKey& a, const InternalKey& b) const;
+  int Compare(const ParsedInternalKey& a, const ParsedInternalKey& b) const;
+  virtual const Comparator* GetRootComparator() const override {
+    return user_comparator_.GetRootComparator();
+  }
+};
+
+// The class represent the internal key in encoded form.
+class InternalKey {
+ private:
+  std::string rep_;
+
+ public:
+  InternalKey() {}  // Leave rep_ as empty to indicate it is invalid
+  InternalKey(const Slice& _user_key, SequenceNumber s, ValueType t) {
+    AppendInternalKey(&rep_, ParsedInternalKey(_user_key, s, t));
+  }
+
+  // sets the internal key to be bigger or equal to all internal keys with this
+  // user key
+  void SetMaxPossibleForUserKey(const Slice& _user_key) {
+    AppendInternalKey(
+        &rep_, ParsedInternalKey(_user_key, 0, static_cast<ValueType>(0)));
+  }
+
+  // sets the internal key to be smaller or equal to all internal keys with this
+  // user key
+  void SetMinPossibleForUserKey(const Slice& _user_key) {
+    AppendInternalKey(&rep_, ParsedInternalKey(_user_key, kMaxSequenceNumber,
+                                               kValueTypeForSeek));
+  }
+
+  bool Valid() const {
+    ParsedInternalKey parsed;
+    return ParseInternalKey(Slice(rep_), &parsed);
+  }
+
+  void DecodeFrom(const Slice& s) { rep_.assign(s.data(), s.size()); }
+  Slice Encode() const {
+    assert(!rep_.empty());
+    return rep_;
+  }
+
+  Slice user_key() const { return ExtractUserKey(rep_); }
+  size_t size() { return rep_.size(); }
+
+  void Set(const Slice& _user_key, SequenceNumber s, ValueType t) {
+    SetFrom(ParsedInternalKey(_user_key, s, t));
+  }
+
+  void SetFrom(const ParsedInternalKey& p) {
+    rep_.clear();
+    AppendInternalKey(&rep_, p);
+  }
+
+  void Clear() { rep_.clear(); }
+
+  // The underlying representation.
+  // Intended only to be used together with ConvertFromUserKey().
+  std::string* rep() { return &rep_; }
+
+  // Assuming that *rep() contains a user key, this method makes internal key
+  // out of it in-place. This saves a memcpy compared to Set()/SetFrom().
+  void ConvertFromUserKey(SequenceNumber s, ValueType t) {
+    AppendInternalKeyFooter(&rep_, s, t);
+  }
+
+  std::string DebugString(bool hex = false) const;
+};
+
+inline int InternalKeyComparator::Compare(const InternalKey& a,
+                                          const InternalKey& b) const {
+  return Compare(a.Encode(), b.Encode());
+}
+
+inline bool ParseInternalKey(const Slice& internal_key,
+                             ParsedInternalKey* result) {
+  const size_t n = internal_key.size();
+  if (n < 8) return false;
+  uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
+  unsigned char c = num & 0xff;
+  result->sequence = num >> 8;
+  result->type = static_cast<ValueType>(c);
+  assert(result->type <= ValueType::kMaxValue);
+  result->user_key = Slice(internal_key.data(), n - 8);
+  return IsExtendedValueType(result->type);
+}
+
+// Update the sequence number in the internal key.
+// Guarantees not to invalidate ikey.data().
+inline void UpdateInternalKey(std::string* ikey, uint64_t seq, ValueType t) {
+  size_t ikey_sz = ikey->size();
+  assert(ikey_sz >= 8);
+  uint64_t newval = (seq << 8) | t;
+
+  // Note: Since C++11, strings are guaranteed to be stored contiguously and
+  // string::operator[]() is guaranteed not to change ikey.data().
+  EncodeFixed64(&(*ikey)[ikey_sz - 8], newval);
+}
+
+// Get the sequence number from the internal key
+inline uint64_t GetInternalKeySeqno(const Slice& internal_key) {
+  const size_t n = internal_key.size();
+  assert(n >= 8);
+  uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
+  return num >> 8;
+}
+
+// The class to store keys in an efficient way. It allows:
+// 1. Users can either copy the key into it, or have it point to an unowned
+//    address.
+// 2. For copied key, a short inline buffer is kept to reduce memory
+//    allocation for smaller keys.
+// 3. It tracks user key or internal key, and allow conversion between them.
+class IterKey {
+ public:
+  IterKey()
+      : buf_(space_),
+        key_(buf_),
+        key_size_(0),
+        buf_size_(sizeof(space_)),
+        is_user_key_(true) {}
+  // No copying allowed
+  IterKey(const IterKey&) = delete;
+  void operator=(const IterKey&) = delete;
+
+  ~IterKey() { ResetBuffer(); }
+
+  // The bool will be picked up by the next calls to SetKey
+  void SetIsUserKey(bool is_user_key) { is_user_key_ = is_user_key; }
+
+  // Returns the key in whichever format that was provided to KeyIter
+  Slice GetKey() const { return Slice(key_, key_size_); }
+
+  Slice GetInternalKey() const {
+    assert(!IsUserKey());
+    return Slice(key_, key_size_);
+  }
+
+  Slice GetUserKey() const {
+    if (IsUserKey()) {
+      return Slice(key_, key_size_);
+    } else {
+      assert(key_size_ >= 8);
+      return Slice(key_, key_size_ - 8);
+    }
+  }
+
+  size_t Size() const { return key_size_; }
+
+  void Clear() { key_size_ = 0; }
+
+  // Append "non_shared_data" to its back, from "shared_len"
+  // This function is used in Block::Iter::ParseNextKey
+  // shared_len: bytes in [0, shard_len-1] would be remained
+  // non_shared_data: data to be append, its length must be >= non_shared_len
+  void TrimAppend(const size_t shared_len, const char* non_shared_data,
+                  const size_t non_shared_len) {
+    assert(shared_len <= key_size_);
+    size_t total_size = shared_len + non_shared_len;
+
+    if (IsKeyPinned() /* key is not in buf_ */) {
+      // Copy the key from external memory to buf_ (copy shared_len bytes)
+      EnlargeBufferIfNeeded(total_size);
+      memcpy(buf_, key_, shared_len);
+    } else if (total_size > buf_size_) {
+      // Need to allocate space, delete previous space
+      char* p = new char[total_size];
+      memcpy(p, key_, shared_len);
+
+      if (buf_ != space_) {
+        delete[] buf_;
+      }
+
+      buf_ = p;
+      buf_size_ = total_size;
+    }
+
+    memcpy(buf_ + shared_len, non_shared_data, non_shared_len);
+    key_ = buf_;
+    key_size_ = total_size;
+  }
+
+  Slice SetKey(const Slice& key, bool copy = true) {
+    // is_user_key_ expected to be set already via SetIsUserKey
+    return SetKeyImpl(key, copy);
+  }
+
+  Slice SetUserKey(const Slice& key, bool copy = true) {
+    is_user_key_ = true;
+    return SetKeyImpl(key, copy);
+  }
+
+  Slice SetInternalKey(const Slice& key, bool copy = true) {
+    is_user_key_ = false;
+    return SetKeyImpl(key, copy);
+  }
+
+  // Copies the content of key, updates the reference to the user key in ikey
+  // and returns a Slice referencing the new copy.
+  Slice SetInternalKey(const Slice& key, ParsedInternalKey* ikey) {
+    size_t key_n = key.size();
+    assert(key_n >= 8);
+    SetInternalKey(key);
+    ikey->user_key = Slice(key_, key_n - 8);
+    return Slice(key_, key_n);
+  }
+
+  // Copy the key into IterKey own buf_
+  void OwnKey() {
+    assert(IsKeyPinned() == true);
+
+    Reserve(key_size_);
+    memcpy(buf_, key_, key_size_);
+    key_ = buf_;
+  }
+
+  // Update the sequence number in the internal key.  Guarantees not to
+  // invalidate slices to the key (and the user key).
+  void UpdateInternalKey(uint64_t seq, ValueType t) {
+    assert(!IsKeyPinned());
+    assert(key_size_ >= 8);
+    uint64_t newval = (seq << 8) | t;
+    EncodeFixed64(&buf_[key_size_ - 8], newval);
+  }
+
+  bool IsKeyPinned() const { return (key_ != buf_); }
+
+  void SetInternalKey(const Slice& key_prefix, const Slice& user_key,
+                      SequenceNumber s,
+                      ValueType value_type = kValueTypeForSeek) {
+    size_t psize = key_prefix.size();
+    size_t usize = user_key.size();
+    EnlargeBufferIfNeeded(psize + usize + sizeof(uint64_t));
+    if (psize > 0) {
+      memcpy(buf_, key_prefix.data(), psize);
+    }
+    memcpy(buf_ + psize, user_key.data(), usize);
+    EncodeFixed64(buf_ + usize + psize, PackSequenceAndType(s, value_type));
+
+    key_ = buf_;
+    key_size_ = psize + usize + sizeof(uint64_t);
+    is_user_key_ = false;
+  }
+
+  void SetInternalKey(const Slice& user_key, SequenceNumber s,
+                      ValueType value_type = kValueTypeForSeek) {
+    SetInternalKey(Slice(), user_key, s, value_type);
+  }
+
+  void Reserve(size_t size) {
+    EnlargeBufferIfNeeded(size);
+    key_size_ = size;
+  }
+
+  void SetInternalKey(const ParsedInternalKey& parsed_key) {
+    SetInternalKey(Slice(), parsed_key);
+  }
+
+  void SetInternalKey(const Slice& key_prefix,
+                      const ParsedInternalKey& parsed_key_suffix) {
+    SetInternalKey(key_prefix, parsed_key_suffix.user_key,
+                   parsed_key_suffix.sequence, parsed_key_suffix.type);
+  }
+
+  void EncodeLengthPrefixedKey(const Slice& key) {
+    auto size = key.size();
+    EnlargeBufferIfNeeded(size + static_cast<size_t>(VarintLength(size)));
+    char* ptr = EncodeVarint32(buf_, static_cast<uint32_t>(size));
+    memcpy(ptr, key.data(), size);
+    key_ = buf_;
+    is_user_key_ = true;
+  }
+
+  bool IsUserKey() const { return is_user_key_; }
+
+ private:
+  char* buf_;
+  const char* key_;
+  size_t key_size_;
+  size_t buf_size_;
+  char space_[32];  // Avoid allocation for short keys
+  bool is_user_key_;
+
+  Slice SetKeyImpl(const Slice& key, bool copy) {
+    size_t size = key.size();
+    if (copy) {
+      // Copy key to buf_
+      EnlargeBufferIfNeeded(size);
+      memcpy(buf_, key.data(), size);
+      key_ = buf_;
+    } else {
+      // Update key_ to point to external memory
+      key_ = key.data();
+    }
+    key_size_ = size;
+    return Slice(key_, key_size_);
+  }
+
+  void ResetBuffer() {
+    if (buf_ != space_) {
+      delete[] buf_;
+      buf_ = space_;
+    }
+    buf_size_ = sizeof(space_);
+    key_size_ = 0;
+  }
+
+  // Enlarge the buffer size if needed based on key_size.
+  // By default, static allocated buffer is used. Once there is a key
+  // larger than the static allocated buffer, another buffer is dynamically
+  // allocated, until a larger key buffer is requested. In that case, we
+  // reallocate buffer and delete the old one.
+  void EnlargeBufferIfNeeded(size_t key_size) {
+    // If size is smaller than buffer size, continue using current buffer,
+    // or the static allocated one, as default
+    if (key_size > buf_size_) {
+      EnlargeBuffer(key_size);
+    }
+  }
+
+  void EnlargeBuffer(size_t key_size);
+};
+
+// Convert from a SliceTranform of user keys, to a SliceTransform of
+// user keys.
+class InternalKeySliceTransform : public SliceTransform {
+ public:
+  explicit InternalKeySliceTransform(const SliceTransform* transform)
+      : transform_(transform) {}
+
+  virtual const char* Name() const override { return transform_->Name(); }
+
+  virtual Slice Transform(const Slice& src) const override {
+    auto user_key = ExtractUserKey(src);
+    return transform_->Transform(user_key);
+  }
+
+  virtual bool InDomain(const Slice& src) const override {
+    auto user_key = ExtractUserKey(src);
+    return transform_->InDomain(user_key);
+  }
+
+  virtual bool InRange(const Slice& dst) const override {
+    auto user_key = ExtractUserKey(dst);
+    return transform_->InRange(user_key);
+  }
+
+  const SliceTransform* user_prefix_extractor() const { return transform_; }
+
+ private:
+  // Like comparator, InternalKeySliceTransform will not take care of the
+  // deletion of transform_
+  const SliceTransform* const transform_;
+};
+
+// Read the key of a record from a write batch.
+// if this record represent the default column family then cf_record
+// must be passed as false, otherwise it must be passed as true.
+extern bool ReadKeyFromWriteBatchEntry(Slice* input, Slice* key,
+                                       bool cf_record);
+
+// Read record from a write batch piece from input.
+// tag, column_family, key, value and blob are return values. Callers own the
+// Slice they point to.
+// Tag is defined as ValueType.
+// input will be advanced to after the record.
+extern Status ReadRecordFromWriteBatch(Slice* input, char* tag,
+                                       uint32_t* column_family, Slice* key,
+                                       Slice* value, Slice* blob, Slice* xid);
+
+// When user call DeleteRange() to delete a range of keys,
+// we will store a serialized RangeTombstone in MemTable and SST.
+// the struct here is a easy-understood form
+// start/end_key_ is the start/end user key of the range to be deleted
+struct RangeTombstone {
+  Slice start_key_;
+  Slice end_key_;
+  SequenceNumber seq_;
+  RangeTombstone() = default;
+  RangeTombstone(Slice sk, Slice ek, SequenceNumber sn)
+      : start_key_(sk), end_key_(ek), seq_(sn) {}
+
+  RangeTombstone(ParsedInternalKey parsed_key, Slice value) {
+    start_key_ = parsed_key.user_key;
+    seq_ = parsed_key.sequence;
+    end_key_ = value;
+  }
+
+  // be careful to use Serialize(), allocates new memory
+  std::pair<InternalKey, Slice> Serialize() const {
+    auto key = InternalKey(start_key_, seq_, kTypeRangeDeletion);
+    Slice value = end_key_;
+    return std::make_pair(std::move(key), std::move(value));
+  }
+
+  // be careful to use SerializeKey(), allocates new memory
+  InternalKey SerializeKey() const {
+    return InternalKey(start_key_, seq_, kTypeRangeDeletion);
+  }
+
+  // The tombstone end-key is exclusive, so we generate an internal-key here
+  // which has a similar property. Using kMaxSequenceNumber guarantees that
+  // the returned internal-key will compare less than any other internal-key
+  // with the same user-key. This in turn guarantees that the serialized
+  // end-key for a tombstone such as [a-b] will compare less than the key "b".
+  //
+  // be careful to use SerializeEndKey(), allocates new memory
+  InternalKey SerializeEndKey() const {
+    return InternalKey(end_key_, kMaxSequenceNumber, kTypeRangeDeletion);
+  }
+};
+
+inline int InternalKeyComparator::Compare(const Slice& akey,
+                                          const Slice& bkey) const {
+  // Order by:
+  //    increasing user key (according to user-supplied comparator)
+  //    decreasing sequence number
+  //    decreasing type (though sequence# should be enough to disambiguate)
+  int r = user_comparator_.Compare(ExtractUserKey(akey), ExtractUserKey(bkey));
+  if (r == 0) {
+    const uint64_t anum = DecodeFixed64(akey.data() + akey.size() - 8);
+    const uint64_t bnum = DecodeFixed64(bkey.data() + bkey.size() - 8);
+    if (anum > bnum) {
+      r = -1;
+    } else if (anum < bnum) {
+      r = +1;
+    }
+  }
+  return r;
+}
+
+inline int InternalKeyComparator::CompareKeySeq(const Slice& akey,
+                                                const Slice& bkey) const {
+  // Order by:
+  //    increasing user key (according to user-supplied comparator)
+  //    decreasing sequence number
+  int r = user_comparator_.Compare(ExtractUserKey(akey), ExtractUserKey(bkey));
+  if (r == 0) {
+    // Shift the number to exclude the last byte which contains the value type
+    const uint64_t anum = DecodeFixed64(akey.data() + akey.size() - 8) >> 8;
+    const uint64_t bnum = DecodeFixed64(bkey.data() + bkey.size() - 8) >> 8;
+    if (anum > bnum) {
+      r = -1;
+    } else if (anum < bnum) {
+      r = +1;
+    }
+  }
+  return r;
+}
+
+// Wrap InternalKeyComparator as a comparator class for ParsedInternalKey.
+struct ParsedInternalKeyComparator {
+  explicit ParsedInternalKeyComparator(const InternalKeyComparator* c)
+      : cmp(c) {}
+
+  bool operator()(const ParsedInternalKey& a,
+                  const ParsedInternalKey& b) const {
+    return cmp->Compare(a, b) < 0;
+  }
+
+  const InternalKeyComparator* cmp;
+};
+
+}  // namespace ROCKSDB_NAMESPACE