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81 рядки
2.5 KiB
81 рядки
2.5 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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//
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// WriteBatch holds a collection of updates to apply atomically to a DB.
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//
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// The updates are applied in the order in which they are added
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// to the WriteBatch. For example, the value of "key" will be "v3"
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// after the following batch is written:
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//
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// batch.Put("key", "v1");
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// batch.Delete("key");
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// batch.Put("key", "v2");
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// batch.Put("key", "v3");
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//
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// Multiple threads can invoke const methods on a WriteBatch without
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// external synchronization, but if any of the threads may call a
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// non-const method, all threads accessing the same WriteBatch must use
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// external synchronization.
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#ifndef STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
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#define STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
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#include <string>
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#include "leveldb/export.h"
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#include "leveldb/status.h"
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namespace leveldb {
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class Slice;
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class LEVELDB_EXPORT WriteBatch {
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public:
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WriteBatch();
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// Intentionally copyable.
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WriteBatch(const WriteBatch&) = default;
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WriteBatch& operator =(const WriteBatch&) = default;
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~WriteBatch();
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// Store the mapping "key->value" in the database.
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void Put(const Slice& key, const Slice& value);
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// If the database contains a mapping for "key", erase it. Else do nothing.
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void Delete(const Slice& key);
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// Clear all updates buffered in this batch.
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void Clear();
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// The size of the database changes caused by this batch.
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//
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// This number is tied to implementation details, and may change across
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// releases. It is intended for LevelDB usage metrics.
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size_t ApproximateSize() const;
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// Copies the operations in "source" to this batch.
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//
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// This runs in O(source size) time. However, the constant factor is better
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// than calling Iterate() over the source batch with a Handler that replicates
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// the operations into this batch.
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void Append(const WriteBatch& source);
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// Support for iterating over the contents of a batch.
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class Handler {
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public:
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virtual ~Handler();
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virtual void Put(const Slice& key, const Slice& value) = 0;
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virtual void Delete(const Slice& key) = 0;
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};
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Status Iterate(Handler* handler) const;
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private:
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friend class WriteBatchInternal;
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std::string rep_; // See comment in write_batch.cc for the format of rep_
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};
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_INCLUDE_WRITE_BATCH_H_
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