blob: c6a471cda4444934fdbcb01639852202819ae634 [file] [log] [blame]
// 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 <memory>
#include <stdint.h>
#include "db/log_format.h"
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
#include "rocksdb/options.h"
namespace rocksdb {
class SequentialFileReader;
class Logger;
using std::unique_ptr;
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 {
// Interface for reporting errors.
class Reporter {
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.
// The Reader will start reading at the first record located at physical
// position >= initial_offset within the file.
Reader(std::shared_ptr<Logger> info_log,
unique_ptr<SequentialFileReader>&& file,
Reporter* reporter, bool checksum, uint64_t initial_offset,
uint64_t log_num);
// 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.
bool ReadRecord(Slice* record, std::string* scratch,
WALRecoveryMode wal_recovery_mode =
// Returns the physical offset of the last record returned by ReadRecord.
// Undefined before the first call to ReadRecord.
uint64_t LastRecordOffset();
// returns true if the reader has encountered an eof condition.
bool IsEOF() {
return eof_;
// 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.
void UnmarkEOF();
SequentialFileReader* file() { return file_.get(); }
std::shared_ptr<Logger> info_log_;
const unique_ptr<SequentialFileReader> file_;
Reporter* const reporter_;
bool const checksum_;
char* const backing_store_;
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_;
// Offset at which to start looking for the first record to return
uint64_t const initial_offset_;
// which log number this is
uint64_t const log_number_;
// Whether this is a recycled log file
bool recycled_;
// 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)
// * The record is below constructor's initial_offset (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,
// Skips all blocks that are completely before "initial_offset_".
// Returns true on success. Handles reporting.
bool SkipToInitialBlock();
// 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);
// 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);
// No copying allowed
Reader(const Reader&);
void operator=(const Reader&);
} // namespace log
} // namespace rocksdb