1// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file. See the AUTHORS file for names of contributors.
4
5#ifndef STORAGE_LEVELDB_DB_MEMTABLE_H_
6#define STORAGE_LEVELDB_DB_MEMTABLE_H_
7
8#include <string>
9#include "leveldb/db.h"
10#include "db/dbformat.h"
11#include "db/skiplist.h"
12#include "util/arena.h"
13
14namespace leveldb {
15
16class InternalKeyComparator;
17class Mutex;
18class MemTableIterator;
19
20class MemTable {
21 public:
22  // MemTables are reference counted.  The initial reference count
23  // is zero and the caller must call Ref() at least once.
24  explicit MemTable(const InternalKeyComparator& comparator);
25
26  // Increase reference count.
27  void Ref() { ++refs_; }
28
29  // Drop reference count.  Delete if no more references exist.
30  void Unref() {
31    --refs_;
32    assert(refs_ >= 0);
33    if (refs_ <= 0) {
34      delete this;
35    }
36  }
37
38  // Returns an estimate of the number of bytes of data in use by this
39  // data structure.
40  //
41  // REQUIRES: external synchronization to prevent simultaneous
42  // operations on the same MemTable.
43  size_t ApproximateMemoryUsage();
44
45  // Return an iterator that yields the contents of the memtable.
46  //
47  // The caller must ensure that the underlying MemTable remains live
48  // while the returned iterator is live.  The keys returned by this
49  // iterator are internal keys encoded by AppendInternalKey in the
50  // db/format.{h,cc} module.
51  Iterator* NewIterator();
52
53  // Add an entry into memtable that maps key to value at the
54  // specified sequence number and with the specified type.
55  // Typically value will be empty if type==kTypeDeletion.
56  void Add(SequenceNumber seq, ValueType type,
57           const Slice& key,
58           const Slice& value);
59
60  // If memtable contains a value for key, store it in *value and return true.
61  // If memtable contains a deletion for key, store a NotFound() error
62  // in *status and return true.
63  // Else, return false.
64  bool Get(const LookupKey& key, std::string* value, Status* s);
65
66 private:
67  ~MemTable();  // Private since only Unref() should be used to delete it
68
69  struct KeyComparator {
70    const InternalKeyComparator comparator;
71    explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) { }
72    int operator()(const char* a, const char* b) const;
73  };
74  friend class MemTableIterator;
75  friend class MemTableBackwardIterator;
76
77  typedef SkipList<const char*, KeyComparator> Table;
78
79  KeyComparator comparator_;
80  int refs_;
81  Arena arena_;
82  Table table_;
83
84  // No copying allowed
85  MemTable(const MemTable&);
86  void operator=(const MemTable&);
87};
88
89}  // namespace leveldb
90
91#endif  // STORAGE_LEVELDB_DB_MEMTABLE_H_
92