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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// 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.
#pragma once
#include <cstdint>
#include <memory>
#include "db/log_format.h"
#include "rocksdb/compression_type.h"
#include "rocksdb/env.h"
#include "rocksdb/io_status.h"
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
#include "util/compression.h"
namespace ROCKSDB_NAMESPACE {
class WritableFileWriter;
namespace log {
/**
* Writer is a general purpose log stream writer. It provides an append-only
* abstraction for writing data. The details of the how the data is written is
* handled by the WritableFile sub-class implementation.
*
* File format:
*
* File is broken down into variable sized records. The format of each record
* is described below.
* +-----+-------------+--+----+----------+------+-- ... ----+
* File | r0 | r1 |P | r2 | r3 | r4 | |
* +-----+-------------+--+----+----------+------+-- ... ----+
* <--- kBlockSize ------>|<-- kBlockSize ------>|
* rn = variable size records
* P = Padding
*
* Data is written out in kBlockSize chunks. If next record does not fit
* into the space left, the leftover space will be padded with \0.
*
* Legacy record format:
*
* +---------+-----------+-----------+--- ... ---+
* |CRC (4B) | Size (2B) | Type (1B) | Payload |
* +---------+-----------+-----------+--- ... ---+
*
* CRC = 32bit hash computed over the record type and payload using CRC
* Size = Length of the payload data
* Type = Type of record
* (kZeroType, kFullType, kFirstType, kLastType, kMiddleType )
* The type is used to group a bunch of records together to represent
* blocks that are larger than kBlockSize
* Payload = Byte stream as long as specified by the payload size
*
* Recyclable record format:
*
* +---------+-----------+-----------+----------------+--- ... ---+
* |CRC (4B) | Size (2B) | Type (1B) | Log number (4B)| Payload |
* +---------+-----------+-----------+----------------+--- ... ---+
*
* Same as above, with the addition of
* Log number = 32bit log file number, so that we can distinguish between
* records written by the most recent log writer vs a previous one.
*/
class Writer {
public:
// Create a writer that will append data to "*dest".
// "*dest" must be initially empty.
// "*dest" must remain live while this Writer is in use.
explicit Writer(std::unique_ptr<WritableFileWriter>&& dest,
uint64_t log_number, bool recycle_log_files,
bool manual_flush = false,
CompressionType compressionType = kNoCompression);
// No copying allowed
Writer(const Writer&) = delete;
void operator=(const Writer&) = delete;
~Writer();
IOStatus AddRecord(const Slice& slice,
Env::IOPriority rate_limiter_priority = Env::IO_TOTAL);
IOStatus AddCompressionTypeRecord();
WritableFileWriter* file() { return dest_.get(); }
const WritableFileWriter* file() const { return dest_.get(); }
uint64_t get_log_number() const { return log_number_; }
IOStatus WriteBuffer();
IOStatus Close();
bool BufferIsEmpty();
private:
std::unique_ptr<WritableFileWriter> dest_;
size_t block_offset_; // Current offset in block
uint64_t log_number_;
bool recycle_log_files_;
// crc32c values for all supported record types. These are
// pre-computed to reduce the overhead of computing the crc of the
// record type stored in the header.
uint32_t type_crc_[kMaxRecordType + 1];
IOStatus EmitPhysicalRecord(
RecordType type, const char* ptr, size_t length,
Env::IOPriority rate_limiter_priority = Env::IO_TOTAL);
// If true, it does not flush after each write. Instead it relies on the upper
// layer to manually does the flush by calling ::WriteBuffer()
bool manual_flush_;
// Compression Type
CompressionType compression_type_;
StreamingCompress* compress_;
// Reusable compressed output buffer
std::unique_ptr<char[]> compressed_buffer_;
};
} // namespace log
} // namespace ROCKSDB_NAMESPACE
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