ceph/src/rocksdb/db/lookup_key.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5 //
   6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   7 // Use of this source code is governed by a BSD-style license that can be
   8 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   9
  10 #pragma once
  11 #include <string>
  12 #include <utility>
  13
  14 #include "rocksdb/slice.h"
  15 #include "rocksdb/types.h"
  16
  17 namespace ROCKSDB_NAMESPACE {
  18
  19 // A helper class useful for DBImpl::Get()
  20 class LookupKey {
  21  public:
  22   // Initialize *this for looking up user_key at a snapshot with
  23   // the specified sequence number.
  24   LookupKey(const Slice& _user_key, SequenceNumber sequence,
  25             const Slice* ts = nullptr);
  26
  27   ~LookupKey();
  28
  29   // Return a key suitable for lookup in a MemTable.
  30   Slice memtable_key() const {
  31     return Slice(start_, static_cast<size_t>(end_ - start_));
  32   }
  33
  34   // Return an internal key (suitable for passing to an internal iterator)
  35   Slice internal_key() const {
  36     return Slice(kstart_, static_cast<size_t>(end_ - kstart_));
  37   }
  38
  39   // Return the user key.
  40   // If user-defined timestamp is enabled, then timestamp is included in the
  41   // result.
  42   Slice user_key() const {
  43     return Slice(kstart_, static_cast<size_t>(end_ - kstart_ - 8));
  44   }
  45
  46  private:
  47   // We construct a char array of the form:
  48   //    klength  varint32               <-- start_
  49   //    userkey  char[klength]          <-- kstart_
  50   //    tag      uint64
  51   //                                    <-- end_
  52   // The array is a suitable MemTable key.
  53   // The suffix starting with "userkey" can be used as an InternalKey.
  54   const char* start_;
  55   const char* kstart_;
  56   const char* end_;
  57   char space_[200];  // Avoid allocation for short keys
  58
  59   // No copying allowed
  60   LookupKey(const LookupKey&);
  61   void operator=(const LookupKey&);
  62 };
  63
  64 inline LookupKey::~LookupKey() {
  65   if (start_ != space_) delete[] start_;
  66 }
  67
  68 }  // namespace ROCKSDB_NAMESPACE