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 14 namespace leveldb { 15 16 class InternalKeyComparator; 17 class Mutex; 18 class MemTableIterator; 19 20 class 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
