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.
5 #ifndef STORAGE_LEVELDB_DB_MEMTABLE_H_
6 #define STORAGE_LEVELDB_DB_MEMTABLE_H_
9 #include "leveldb/db.h"
10 #include "db/dbformat.h"
11 #include "db/skiplist.h"
12 #include "util/arena.h"
16 class InternalKeyComparator;
18 class MemTableIterator;
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);
26 // Increase reference count.
27 void Ref() { ++refs_; }
29 // Drop reference count. Delete if no more references exist.
38 // Returns an estimate of the number of bytes of data in use by this
41 // REQUIRES: external synchronization to prevent simultaneous
42 // operations on the same MemTable.
43 size_t ApproximateMemoryUsage();
45 // Return an iterator that yields the contents of the memtable.
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();
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,
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);
67 ~MemTable(); // Private since only Unref() should be used to delete it
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;
74 friend class MemTableIterator;
75 friend class MemTableBackwardIterator;
77 typedef SkipList<const char*, KeyComparator> Table;
79 KeyComparator comparator_;
85 MemTable(const MemTable&);
86 void operator=(const MemTable&);
89 } // namespace leveldb
91 #endif // STORAGE_LEVELDB_DB_MEMTABLE_H_