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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.
//
// WriteBatch holds a collection of updates to apply atomically to a DB.
//
// The updates are applied in the order in which they are added
// to the WriteBatch. For example, the value of "key" will be "v3"
// after the following batch is written:
//
// batch.Put("key", "v1");
// batch.Delete("key");
// batch.Put("key", "v2");
// batch.Put("key", "v3");
//
// Multiple threads can invoke const methods on a WriteBatch without
// external synchronization, but if any of the threads may call a
// non-const method, all threads accessing the same WriteBatch must use
// external synchronization.
#ifndef STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
#define STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
#include <string>
#include "leveldb/export.h"
#include "leveldb/status.h"
namespace leveldb {
class Slice;
class LEVELDB_EXPORT WriteBatch {
public:
class LEVELDB_EXPORT Handler {
public:
virtual ~Handler();
virtual void Put(const Slice& key, const Slice& value) = 0;
virtual void Delete(const Slice& key) = 0;
};
WriteBatch();
// Intentionally copyable.
WriteBatch(const WriteBatch&) = default;
WriteBatch& operator=(const WriteBatch&) = default;
~WriteBatch();
// Store the mapping "key->value" in the database.
void Put(const Slice& key, const Slice& value);
// If the database contains a mapping for "key", erase it. Else do nothing.
void Delete(const Slice& key);
// Clear all updates buffered in this batch.
void Clear();
// The size of the database changes caused by this batch.
//
// This number is tied to implementation details, and may change across
// releases. It is intended for LevelDB usage metrics.
size_t ApproximateSize() const;
// Copies the operations in "source" to this batch.
//
// This runs in O(source size) time. However, the constant factor is better
// than calling Iterate() over the source batch with a Handler that replicates
// the operations into this batch.
void Append(const WriteBatch& source);
// Support for iterating over the contents of a batch.
Status Iterate(Handler* handler) const;
private:
friend class WriteBatchInternal;
std::string rep_; // See comment in write_batch.cc for the format of rep_
};
} // namespace leveldb
#endif // STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
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