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// 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.
#include <string>
#include "leveldb/db.h"
#include "db/dbformat.h"
#include "db/skiplist.h"
#include "util/arena.h"
namespace leveldb {
class InternalKeyComparator;
class Mutex;
class MemTableIterator;
class MemTable {
// MemTables are reference counted. The initial reference count
// is zero and the caller must call Ref() at least once.
explicit MemTable(const InternalKeyComparator& comparator);
// Increase reference count.
void Ref() { ++refs_; }
// Drop reference count. Delete if no more references exist.
void Unref() {
assert(refs_ >= 0);
if (refs_ <= 0) {
delete this;
// Returns an estimate of the number of bytes of data in use by this
// data structure. It is safe to call when MemTable is being modified.
size_t ApproximateMemoryUsage();
// Return an iterator that yields the contents of the memtable.
// The caller must ensure that the underlying MemTable remains live
// while the returned iterator is live. The keys returned by this
// iterator are internal keys encoded by AppendInternalKey in the
// db/format.{h,cc} module.
Iterator* NewIterator();
// Add an entry into memtable that maps key to value at the
// specified sequence number and with the specified type.
// Typically value will be empty if type==kTypeDeletion.
void Add(SequenceNumber seq, ValueType type,
const Slice& key,
const Slice& value);
// If memtable contains a value for key, store it in *value and return true.
// If memtable contains a deletion for key, store a NotFound() error
// in *status and return true.
// Else, return false.
bool Get(const LookupKey& key, std::string* value, Status* s);
~MemTable(); // Private since only Unref() should be used to delete it
struct KeyComparator {
const InternalKeyComparator comparator;
explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) { }
int operator()(const char* a, const char* b) const;
friend class MemTableIterator;
friend class MemTableBackwardIterator;
typedef SkipList<const char*, KeyComparator> Table;
KeyComparator comparator_;
int refs_;
Arena arena_;
Table table_;
// No copying allowed
MemTable(const MemTable&);
void operator=(const MemTable&);
} // namespace leveldb