da4aa59b4c
Summary: Current `log::Reader` does not perform retry after encountering `EOF`. In the future, we need the log reader to be able to retry tailing the log even after `EOF`. Current implementation is simple. It does not provide more advanced retry policies. Will address this in the future. Pull Request resolved: https://github.com/facebook/rocksdb/pull/4394 Differential Revision: D9926508 Pulled By: riversand963 fbshipit-source-id: d86d145792a41bd64a72f642a2a08c7b7b5201e1
410 lines
13 KiB
C++
410 lines
13 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// 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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#include "db/log_reader.h"
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#include <stdio.h>
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#include "rocksdb/env.h"
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#include "util/coding.h"
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#include "util/crc32c.h"
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#include "util/file_reader_writer.h"
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#include "util/util.h"
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namespace rocksdb {
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namespace log {
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Reader::Reporter::~Reporter() {
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}
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Reader::Reader(std::shared_ptr<Logger> info_log,
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unique_ptr<SequentialFileReader>&& _file, Reporter* reporter,
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bool checksum, uint64_t log_num, bool retry_after_eof)
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: info_log_(info_log),
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file_(std::move(_file)),
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reporter_(reporter),
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checksum_(checksum),
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backing_store_(new char[kBlockSize]),
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buffer_(),
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eof_(false),
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read_error_(false),
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eof_offset_(0),
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last_record_offset_(0),
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end_of_buffer_offset_(0),
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log_number_(log_num),
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recycled_(false),
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retry_after_eof_(retry_after_eof) {}
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Reader::~Reader() {
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delete[] backing_store_;
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}
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// For kAbsoluteConsistency, on clean shutdown we don't expect any error
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// in the log files. For other modes, we can ignore only incomplete records
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// in the last log file, which are presumably due to a write in progress
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// during restart (or from log recycling).
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//
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// TODO krad: Evaluate if we need to move to a more strict mode where we
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// restrict the inconsistency to only the last log
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bool Reader::ReadRecord(Slice* record, std::string* scratch,
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WALRecoveryMode wal_recovery_mode) {
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scratch->clear();
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record->clear();
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bool in_fragmented_record = false;
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// Record offset of the logical record that we're reading
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// 0 is a dummy value to make compilers happy
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uint64_t prospective_record_offset = 0;
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Slice fragment;
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while (true) {
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uint64_t physical_record_offset = end_of_buffer_offset_ - buffer_.size();
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size_t drop_size = 0;
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const unsigned int record_type = ReadPhysicalRecord(&fragment, &drop_size);
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switch (record_type) {
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case kFullType:
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case kRecyclableFullType:
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if (in_fragmented_record && !scratch->empty()) {
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// Handle bug in earlier versions of log::Writer where
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// it could emit an empty kFirstType record at the tail end
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// of a block followed by a kFullType or kFirstType record
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// at the beginning of the next block.
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ReportCorruption(scratch->size(), "partial record without end(1)");
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}
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prospective_record_offset = physical_record_offset;
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scratch->clear();
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*record = fragment;
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last_record_offset_ = prospective_record_offset;
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return true;
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case kFirstType:
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case kRecyclableFirstType:
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if (in_fragmented_record && !scratch->empty()) {
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// Handle bug in earlier versions of log::Writer where
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// it could emit an empty kFirstType record at the tail end
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// of a block followed by a kFullType or kFirstType record
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// at the beginning of the next block.
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ReportCorruption(scratch->size(), "partial record without end(2)");
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}
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prospective_record_offset = physical_record_offset;
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scratch->assign(fragment.data(), fragment.size());
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in_fragmented_record = true;
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break;
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case kMiddleType:
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case kRecyclableMiddleType:
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if (!in_fragmented_record) {
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ReportCorruption(fragment.size(),
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"missing start of fragmented record(1)");
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} else {
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scratch->append(fragment.data(), fragment.size());
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}
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break;
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case kLastType:
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case kRecyclableLastType:
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if (!in_fragmented_record) {
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ReportCorruption(fragment.size(),
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"missing start of fragmented record(2)");
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} else {
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scratch->append(fragment.data(), fragment.size());
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*record = Slice(*scratch);
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last_record_offset_ = prospective_record_offset;
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return true;
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}
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break;
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case kBadHeader:
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if (wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
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// in clean shutdown we don't expect any error in the log files
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ReportCorruption(drop_size, "truncated header");
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}
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FALLTHROUGH_INTENDED;
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case kEof:
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if (in_fragmented_record) {
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if (wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
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// in clean shutdown we don't expect any error in the log files
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ReportCorruption(scratch->size(), "error reading trailing data");
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}
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// This can be caused by the writer dying immediately after
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// writing a physical record but before completing the next; don't
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// treat it as a corruption, just ignore the entire logical record.
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scratch->clear();
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}
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return false;
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case kOldRecord:
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if (wal_recovery_mode != WALRecoveryMode::kSkipAnyCorruptedRecords) {
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// Treat a record from a previous instance of the log as EOF.
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if (in_fragmented_record) {
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if (wal_recovery_mode == WALRecoveryMode::kAbsoluteConsistency) {
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// in clean shutdown we don't expect any error in the log files
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ReportCorruption(scratch->size(), "error reading trailing data");
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}
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// This can be caused by the writer dying immediately after
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// writing a physical record but before completing the next; don't
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// treat it as a corruption, just ignore the entire logical record.
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scratch->clear();
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}
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return false;
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}
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FALLTHROUGH_INTENDED;
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case kBadRecord:
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if (in_fragmented_record) {
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ReportCorruption(scratch->size(), "error in middle of record");
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in_fragmented_record = false;
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scratch->clear();
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}
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break;
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case kBadRecordLen:
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case kBadRecordChecksum:
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if (recycled_ &&
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wal_recovery_mode ==
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WALRecoveryMode::kTolerateCorruptedTailRecords) {
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scratch->clear();
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return false;
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}
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if (record_type == kBadRecordLen) {
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ReportCorruption(drop_size, "bad record length");
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} else {
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ReportCorruption(drop_size, "checksum mismatch");
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}
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if (in_fragmented_record) {
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ReportCorruption(scratch->size(), "error in middle of record");
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in_fragmented_record = false;
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scratch->clear();
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}
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break;
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default: {
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char buf[40];
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snprintf(buf, sizeof(buf), "unknown record type %u", record_type);
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ReportCorruption(
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(fragment.size() + (in_fragmented_record ? scratch->size() : 0)),
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buf);
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in_fragmented_record = false;
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scratch->clear();
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break;
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}
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}
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}
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return false;
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}
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uint64_t Reader::LastRecordOffset() {
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return last_record_offset_;
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}
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void Reader::UnmarkEOF() {
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if (read_error_) {
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return;
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}
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eof_ = false;
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// If retry_after_eof_ is true, we have to proceed to read anyway.
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if (!retry_after_eof_ && eof_offset_ == 0) {
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return;
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}
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// If the EOF was in the middle of a block (a partial block was read) we have
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// to read the rest of the block as ReadPhysicalRecord can only read full
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// blocks and expects the file position indicator to be aligned to the start
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// of a block.
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//
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// consumed_bytes + buffer_size() + remaining == kBlockSize
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size_t consumed_bytes = eof_offset_ - buffer_.size();
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size_t remaining = kBlockSize - eof_offset_;
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// backing_store_ is used to concatenate what is left in buffer_ and
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// the remainder of the block. If buffer_ already uses backing_store_,
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// we just append the new data.
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if (buffer_.data() != backing_store_ + consumed_bytes) {
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// Buffer_ does not use backing_store_ for storage.
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// Copy what is left in buffer_ to backing_store.
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memmove(backing_store_ + consumed_bytes, buffer_.data(), buffer_.size());
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}
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Slice read_buffer;
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Status status = file_->Read(remaining, &read_buffer,
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backing_store_ + eof_offset_);
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size_t added = read_buffer.size();
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end_of_buffer_offset_ += added;
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if (!status.ok()) {
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if (added > 0) {
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ReportDrop(added, status);
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}
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read_error_ = true;
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return;
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}
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if (read_buffer.data() != backing_store_ + eof_offset_) {
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// Read did not write to backing_store_
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memmove(backing_store_ + eof_offset_, read_buffer.data(),
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read_buffer.size());
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}
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buffer_ = Slice(backing_store_ + consumed_bytes,
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eof_offset_ + added - consumed_bytes);
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if (added < remaining) {
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eof_ = true;
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eof_offset_ += added;
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} else {
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eof_offset_ = 0;
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}
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}
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void Reader::ReportCorruption(size_t bytes, const char* reason) {
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ReportDrop(bytes, Status::Corruption(reason));
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}
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void Reader::ReportDrop(size_t bytes, const Status& reason) {
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if (reporter_ != nullptr) {
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reporter_->Corruption(bytes, reason);
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}
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}
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bool Reader::ReadMore(size_t* drop_size, int *error) {
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if (!eof_ && !read_error_) {
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// Last read was a full read, so this is a trailer to skip
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buffer_.clear();
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Status status = file_->Read(kBlockSize, &buffer_, backing_store_);
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end_of_buffer_offset_ += buffer_.size();
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if (!status.ok()) {
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buffer_.clear();
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ReportDrop(kBlockSize, status);
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read_error_ = true;
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*error = kEof;
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return false;
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} else if (buffer_.size() < static_cast<size_t>(kBlockSize)) {
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eof_ = true;
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eof_offset_ = buffer_.size();
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TEST_SYNC_POINT("LogReader::ReadMore:FirstEOF");
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}
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return true;
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} else if (retry_after_eof_ && !read_error_) {
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UnmarkEOF();
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return !read_error_;
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} else {
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// Note that if buffer_ is non-empty, we have a truncated header at the
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// end of the file, which can be caused by the writer crashing in the
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// middle of writing the header. Unless explicitly requested we don't
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// considering this an error, just report EOF.
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if (buffer_.size()) {
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*drop_size = buffer_.size();
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buffer_.clear();
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*error = kBadHeader;
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return false;
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}
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buffer_.clear();
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*error = kEof;
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return false;
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}
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}
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unsigned int Reader::ReadPhysicalRecord(Slice* result, size_t* drop_size) {
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while (true) {
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// We need at least the minimum header size
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if (buffer_.size() < static_cast<size_t>(kHeaderSize)) {
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int r;
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if (!ReadMore(drop_size, &r)) {
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return r;
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}
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continue;
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}
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// Parse the header
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const char* header = buffer_.data();
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const uint32_t a = static_cast<uint32_t>(header[4]) & 0xff;
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const uint32_t b = static_cast<uint32_t>(header[5]) & 0xff;
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const unsigned int type = header[6];
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const uint32_t length = a | (b << 8);
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int header_size = kHeaderSize;
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if (type >= kRecyclableFullType && type <= kRecyclableLastType) {
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if (end_of_buffer_offset_ - buffer_.size() == 0) {
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recycled_ = true;
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}
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header_size = kRecyclableHeaderSize;
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// We need enough for the larger header
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if (buffer_.size() < static_cast<size_t>(kRecyclableHeaderSize)) {
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int r;
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if (!ReadMore(drop_size, &r)) {
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return r;
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}
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continue;
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}
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const uint32_t log_num = DecodeFixed32(header + 7);
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if (log_num != log_number_) {
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return kOldRecord;
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}
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}
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if (header_size + length > buffer_.size()) {
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if (!retry_after_eof_) {
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*drop_size = buffer_.size();
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buffer_.clear();
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if (!eof_) {
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return kBadRecordLen;
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}
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// If the end of the file has been reached without reading |length|
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// bytes of payload, assume the writer died in the middle of writing the
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// record. Don't report a corruption unless requested.
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if (*drop_size) {
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return kBadHeader;
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}
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} else {
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int r;
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if (!ReadMore(drop_size, &r)) {
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return r;
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}
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continue;
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}
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return kEof;
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}
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if (type == kZeroType && length == 0) {
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// Skip zero length record without reporting any drops since
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// such records are produced by the mmap based writing code in
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// env_posix.cc that preallocates file regions.
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// NOTE: this should never happen in DB written by new RocksDB versions,
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// since we turn off mmap writes to manifest and log files
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buffer_.clear();
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return kBadRecord;
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}
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// Check crc
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if (checksum_) {
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uint32_t expected_crc = crc32c::Unmask(DecodeFixed32(header));
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uint32_t actual_crc = crc32c::Value(header + 6, length + header_size - 6);
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if (actual_crc != expected_crc) {
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// Drop the rest of the buffer since "length" itself may have
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// been corrupted and if we trust it, we could find some
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// fragment of a real log record that just happens to look
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// like a valid log record.
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*drop_size = buffer_.size();
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buffer_.clear();
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return kBadRecordChecksum;
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}
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}
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buffer_.remove_prefix(header_size + length);
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*result = Slice(header + header_size, length);
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return type;
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}
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}
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} // namespace log
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} // namespace rocksdb
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