71e0f695c1
Summary: As title. Exposed a Count function that returns the number of updates in a batch. Could be handy for replication sequence number check. Test Plan: make check; Reviewers: emayanke, sheki, dhruba CC: leveldb Differential Revision: https://reviews.facebook.net/D11523
82 lines
2.5 KiB
C++
82 lines
2.5 KiB
C++
// 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/status.h"
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namespace leveldb {
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class Slice;
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class WriteBatch {
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public:
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WriteBatch();
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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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// Merge "value" with the existing value of "key" in the database.
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// "key->merge(existing, value)"
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void Merge(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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// 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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// Merge is not pure virtual. Otherwise, we would break existing
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// clients of Handler on a source code level.
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// The default implementation simply throws a runtime exception.
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virtual void Merge(const Slice& key, const Slice& value);
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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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// Retrieve the serialized version of this batch.
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std::string Data() { return rep_; }
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// Returns the number of updates in the batch
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int Count() const;
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// Constructor with a serialized string object
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WriteBatch(std::string rep): rep_(rep) {}
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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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// Intentionally copyable
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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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