05e8854085
Summary: This diff introduces a new Merge operation into rocksdb. The purpose of this review is mostly getting feedback from the team (everyone please) on the design. Please focus on the four files under include/leveldb/, as they spell the client visible interface change. include/leveldb/db.h include/leveldb/merge_operator.h include/leveldb/options.h include/leveldb/write_batch.h Please go over local/my_test.cc carefully, as it is a concerete use case. Please also review the impelmentation files to see if the straw man implementation makes sense. Note that, the diff does pass all make check and truly supports forward iterator over db and a version of Get that's based on iterator. Future work: - Integration with compaction - A raw Get implementation I am working on a wiki that explains the design and implementation choices, but coding comes just naturally and I think it might be a good idea to share the code earlier. The code is heavily commented. Test Plan: run all local tests Reviewers: dhruba, heyongqiang Reviewed By: dhruba CC: leveldb, zshao, sheki, emayanke, MarkCallaghan Differential Revision: https://reviews.facebook.net/D9651
79 lines
2.4 KiB
C++
79 lines
2.4 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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// Retrive the serialized version of this batch.
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std::string Data() { return rep_; }
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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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