0307c5fe3a
Summary: This patch adds the ability for the user to add sequences of arbitrary data (blobs) to write batches. These blobs are saved to the log along with everything else in the write batch. You can add multiple blobs per WriteBatch and the ordering of blobs, puts, merges, and deletes are preserved. Blobs are not saves to SST files. RocksDB ignores blobs in every way except for writing them to the log. Before committing this patch, I need to add some test code. But I'm submitting it now so people can comment on the API. Test Plan: make -j32 check Reviewers: dhruba, haobo, vamsi Reviewed By: dhruba CC: leveldb Differential Revision: https://reviews.facebook.net/D12195
95 lines
3.2 KiB
C++
95 lines
3.2 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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// Append a blob of arbitrary to the records in this batch. The blob will be
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// stored in the transaction log but not in any other file. In particular, it
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// will not be persisted to the SST files. When iterating over this
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// WriteBatch, WriteBatch::Handler::LogData will be called with the contents
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// of the blob as it is encountered. Blobs, puts, deletes, and merges will be
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// encountered in the same order in thich they were inserted.
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//
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// Example application: add timestamps to the transaction log for use in
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// replication.
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void PutLogData(const Slice& blob);
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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 and LogData are not pure virtual. Otherwise, we would break
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// existing clients of Handler on a source code level. The default
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// implementation of Merge simply throws a runtime exception.
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virtual void Merge(const Slice& key, const Slice& value);
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// The default implementation of LogData does nothing.
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virtual void LogData(const Slice& blob);
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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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explicit 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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