rocksdb/db/log_reader.h
Siddhartha Roychowdhury fec4403ff1 Integrate WAL compression into log reader/writer. (#9642)
Summary:
Integrate the streaming compress/uncompress API into WAL compression.
The streaming compression object is stored in the log_writer along with a reusable output buffer to store the compressed buffer(s).
The streaming uncompress object is stored in the log_reader along with a reusable output buffer to store the uncompressed buffer(s).

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9642

Test Plan:
Added unit tests to verify different scenarios - large buffers, split compressed buffers, etc.

Future optimizations:
The overhead for small records is quite high, so it makes sense to compress only buffers above a certain threshold and use a separate record type to indicate that those records are compressed.

Reviewed By: anand1976

Differential Revision: D34709167

Pulled By: sidroyc

fbshipit-source-id: a37a3cd1301adff6152fb3fcd23726106af07dd4
2022-03-09 15:49:53 -08:00

209 lines
7.2 KiB
C++

// 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 <stdint.h>
#include <memory>
#include "db/log_format.h"
#include "file/sequence_file_reader.h"
#include "rocksdb/options.h"
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
#include "util/compression.h"
namespace ROCKSDB_NAMESPACE {
class Logger;
namespace log {
/**
* Reader is a general purpose log stream reader implementation. The actual job
* of reading from the device is implemented by the SequentialFile interface.
*
* Please see Writer for details on the file and record layout.
*/
class Reader {
public:
// Interface for reporting errors.
class Reporter {
public:
virtual ~Reporter();
// Some corruption was detected. "size" is the approximate number
// of bytes dropped due to the corruption.
virtual void Corruption(size_t bytes, const Status& status) = 0;
};
// Create a reader that will return log records from "*file".
// "*file" must remain live while this Reader is in use.
//
// If "reporter" is non-nullptr, it is notified whenever some data is
// dropped due to a detected corruption. "*reporter" must remain
// live while this Reader is in use.
//
// If "checksum" is true, verify checksums if available.
Reader(std::shared_ptr<Logger> info_log,
std::unique_ptr<SequentialFileReader>&& file, Reporter* reporter,
bool checksum, uint64_t log_num);
// No copying allowed
Reader(const Reader&) = delete;
void operator=(const Reader&) = delete;
virtual ~Reader();
// Read the next record into *record. Returns true if read
// successfully, false if we hit end of the input. May use
// "*scratch" as temporary storage. The contents filled in *record
// will only be valid until the next mutating operation on this
// reader or the next mutation to *scratch.
virtual bool ReadRecord(Slice* record, std::string* scratch,
WALRecoveryMode wal_recovery_mode =
WALRecoveryMode::kTolerateCorruptedTailRecords);
// Returns the physical offset of the last record returned by ReadRecord.
//
// Undefined before the first call to ReadRecord.
uint64_t LastRecordOffset();
// Returns the first physical offset after the last record returned by
// ReadRecord, or zero before first call to ReadRecord. This can also be
// thought of as the "current" position in processing the file bytes.
uint64_t LastRecordEnd();
// returns true if the reader has encountered an eof condition.
bool IsEOF() {
return eof_;
}
// returns true if the reader has encountered read error.
bool hasReadError() const { return read_error_; }
// when we know more data has been written to the file. we can use this
// function to force the reader to look again in the file.
// Also aligns the file position indicator to the start of the next block
// by reading the rest of the data from the EOF position to the end of the
// block that was partially read.
virtual void UnmarkEOF();
SequentialFileReader* file() { return file_.get(); }
Reporter* GetReporter() const { return reporter_; }
uint64_t GetLogNumber() const { return log_number_; }
size_t GetReadOffset() const {
return static_cast<size_t>(end_of_buffer_offset_);
}
protected:
std::shared_ptr<Logger> info_log_;
const std::unique_ptr<SequentialFileReader> file_;
Reporter* const reporter_;
bool const checksum_;
char* const backing_store_;
// Internal state variables used for reading records
Slice buffer_;
bool eof_; // Last Read() indicated EOF by returning < kBlockSize
bool read_error_; // Error occurred while reading from file
// Offset of the file position indicator within the last block when an
// EOF was detected.
size_t eof_offset_;
// Offset of the last record returned by ReadRecord.
uint64_t last_record_offset_;
// Offset of the first location past the end of buffer_.
uint64_t end_of_buffer_offset_;
// which log number this is
uint64_t const log_number_;
// Whether this is a recycled log file
bool recycled_;
// Whether the first record has been read or not.
bool first_record_read_;
// Type of compression used
CompressionType compression_type_;
// Track whether the compression type record has been read or not.
bool compression_type_record_read_;
StreamingUncompress* uncompress_;
// Reusable uncompressed output buffer
std::unique_ptr<char[]> uncompressed_buffer_;
// Reusable uncompressed record
std::string uncompressed_record_;
// Extend record types with the following special values
enum {
kEof = kMaxRecordType + 1,
// Returned whenever we find an invalid physical record.
// Currently there are three situations in which this happens:
// * The record has an invalid CRC (ReadPhysicalRecord reports a drop)
// * The record is a 0-length record (No drop is reported)
kBadRecord = kMaxRecordType + 2,
// Returned when we fail to read a valid header.
kBadHeader = kMaxRecordType + 3,
// Returned when we read an old record from a previous user of the log.
kOldRecord = kMaxRecordType + 4,
// Returned when we get a bad record length
kBadRecordLen = kMaxRecordType + 5,
// Returned when we get a bad record checksum
kBadRecordChecksum = kMaxRecordType + 6,
};
// Return type, or one of the preceding special values
unsigned int ReadPhysicalRecord(Slice* result, size_t* drop_size);
// Read some more
bool ReadMore(size_t* drop_size, int *error);
void UnmarkEOFInternal();
// Reports dropped bytes to the reporter.
// buffer_ must be updated to remove the dropped bytes prior to invocation.
void ReportCorruption(size_t bytes, const char* reason);
void ReportDrop(size_t bytes, const Status& reason);
void InitCompression(const CompressionTypeRecord& compression_record);
};
class FragmentBufferedReader : public Reader {
public:
FragmentBufferedReader(std::shared_ptr<Logger> info_log,
std::unique_ptr<SequentialFileReader>&& _file,
Reporter* reporter, bool checksum, uint64_t log_num)
: Reader(info_log, std::move(_file), reporter, checksum, log_num),
fragments_(),
in_fragmented_record_(false) {}
~FragmentBufferedReader() override {}
bool ReadRecord(Slice* record, std::string* scratch,
WALRecoveryMode wal_recovery_mode =
WALRecoveryMode::kTolerateCorruptedTailRecords) override;
void UnmarkEOF() override;
private:
std::string fragments_;
bool in_fragmented_record_;
bool TryReadFragment(Slice* result, size_t* drop_size,
unsigned int* fragment_type_or_err);
bool TryReadMore(size_t* drop_size, int* error);
// No copy allowed
FragmentBufferedReader(const FragmentBufferedReader&);
void operator=(const FragmentBufferedReader&);
};
} // namespace log
} // namespace ROCKSDB_NAMESPACE