rocksdb/db/lookup_key.h

//  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 <string>
#include <utility>
#include "rocksdb/db.h"
#include "rocksdb/slice.h"
#include "rocksdb/types.h"

namespace rocksdb {

// A helper class useful for DBImpl::Get()
class LookupKey {
 public:
  // Initialize *this for looking up user_key at a snapshot with
  // the specified sequence number.
  LookupKey(const Slice& _user_key, SequenceNumber sequence);

  ~LookupKey();

  // Return a key suitable for lookup in a MemTable.
  Slice memtable_key() const {
    return Slice(start_, static_cast<size_t>(end_ - start_));
  }

  // Return an internal key (suitable for passing to an internal iterator)
  Slice internal_key() const {
    return Slice(kstart_, static_cast<size_t>(end_ - kstart_));
  }

  // Return the user key
  Slice user_key() const {
    return Slice(kstart_, static_cast<size_t>(end_ - kstart_ - 8));
  }

 private:
  // We construct a char array of the form:
  //    klength  varint32               <-- start_
  //    userkey  char[klength]          <-- kstart_
  //    tag      uint64
  //                                    <-- end_
  // The array is a suitable MemTable key.
  // The suffix starting with "userkey" can be used as an InternalKey.
  const char* start_;
  const char* kstart_;
  const char* end_;
  char space_[200];  // Avoid allocation for short keys

  // No copying allowed
  LookupKey(const LookupKey&);
  void operator=(const LookupKey&);
};

inline LookupKey::~LookupKey() {
  if (start_ != space_) delete[] start_;
}

}  // namespace rocksdb