Define WAL related classes to be used in VersionEdit and VersionSet (#7164)
Summary: `WalAddition`, `WalDeletion` are defined in `wal_version.h` and used in `VersionEdit`. `WalAddition` is used to represent events of creating a new WAL (no size, just log number), or closing a WAL (with size). `WalDeletion` is used to represent events of deleting or archiving a WAL, it means the WAL is no longer alive (won't be replayed during recovery). `WalSet` is the set of alive WALs kept in `VersionSet`. 1. Why use `WalDeletion` instead of relying on `MinLogNumber` to identify outdated WALs On recovery, we can compute `MinLogNumber()` based on the log numbers kept in MANIFEST, any log with number < MinLogNumber can be ignored. So it seems that we don't need to persist `WalDeletion` to MANIFEST, since we can ignore the WALs based on MinLogNumber. But the `MinLogNumber()` is actually a lower bound, it does not exactly mean that logs starting from MinLogNumber must exist. This is because in a corner case, when a column family is empty and never flushed, its log number is set to the largest log number, but not persisted in MANIFEST. So let's say there are 2 column families, when creating the DB, the first WAL has log number 1, so it's persisted to MANIFEST for both column families. Then CF 0 is empty and never flushed, CF 1 is updated and flushed, so a new WAL with log number 2 is created and persisted to MANIFEST for CF 1. But CF 0's log number in MANIFEST is still 1. So on recovery, MinLogNumber is 1, but since log 1 only contains data for CF 1, and CF 1 is flushed, log 1 might have already been deleted from disk. We can make `MinLogNumber()` be the exactly minimum log number that must exist, by persisting the most recent log number for empty column families that are not flushed. But if there are N such column families, then every time a new WAL is created, we need to add N records to MANIFEST. In current design, a record is persisted to MANIFEST only when WAL is created, closed, or deleted/archived, so the number of WAL related records are bounded to 3x number of WALs. 2. Why keep `WalSet` in `VersionSet` instead of applying the `VersionEdit`s to `VersionStorageInfo` `VersionEdit`s are originally designed to track the addition and deletion of SST files. The SST files are related to column families, each column family has a list of `Version`s, and each `Version` keeps the set of active SST files in `VersionStorageInfo`. But WALs are a concept of DB, they are not bounded to specific column families. So logically it does not make sense to store WALs in a column family's `Version`s. Also, `Version`'s purpose is to keep reference to SST / blob files, so that they are not deleted until there is no version referencing them. But a WAL is deleted regardless of version references. So we keep the WALs in `VersionSet` for the purpose of writing out the DB state's snapshot when creating new MANIFESTs. Pull Request resolved: https://github.com/facebook/rocksdb/pull/7164 Test Plan: make version_edit_test && ./version_edit_test make wal_edit_test && ./wal_edit_test Reviewed By: ltamasi Differential Revision: D22677936 Pulled By: cheng-chang fbshipit-source-id: 5a3b6890140e572ffd79eb37e6e4c3c32361a859main
Cheng Chang
4 years ago
committed by
Facebook GitHub Bot
parent
124fbd96d8
commit
cd48ecaa1a
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// 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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#include "db/wal_edit.h" |
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#include "rocksdb/slice.h" |
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#include "rocksdb/status.h" |
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#include "util/coding.h" |
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namespace ROCKSDB_NAMESPACE { |
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void WalAddition::EncodeTo(std::string* dst) const { |
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PutVarint64(dst, number_); |
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if (metadata_.HasSize()) { |
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PutVarint32(dst, static_cast<uint32_t>(WalAdditionTag::kSize)); |
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PutVarint64(dst, metadata_.GetSizeInBytes()); |
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} |
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PutVarint32(dst, static_cast<uint32_t>(WalAdditionTag::kTerminate)); |
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} |
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Status WalAddition::DecodeFrom(Slice* src) { |
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constexpr char class_name[] = "WalAddition"; |
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if (!GetVarint64(src, &number_)) { |
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return Status::Corruption(class_name, "Error decoding WAL log number"); |
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} |
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while (true) { |
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uint32_t tag_value = 0; |
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if (!GetVarint32(src, &tag_value)) { |
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return Status::Corruption(class_name, "Error decoding tag"); |
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} |
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WalAdditionTag tag = static_cast<WalAdditionTag>(tag_value); |
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switch (tag) { |
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case WalAdditionTag::kSize: { |
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uint64_t size = 0; |
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if (!GetVarint64(src, &size)) { |
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return Status::Corruption(class_name, "Error decoding WAL file size"); |
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} |
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metadata_.SetSizeInBytes(size); |
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break; |
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} |
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// TODO: process future tags such as checksum.
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case WalAdditionTag::kTerminate: |
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return Status::OK(); |
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default: { |
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std::stringstream ss; |
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ss << "Unknown tag " << tag_value; |
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return Status::Corruption(class_name, ss.str()); |
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} |
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} |
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} |
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} |
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JSONWriter& operator<<(JSONWriter& jw, const WalAddition& wal) { |
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jw << "LogNumber" << wal.GetLogNumber() << "SizeInBytes" |
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<< wal.GetMetadata().GetSizeInBytes(); |
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return jw; |
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} |
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std::ostream& operator<<(std::ostream& os, const WalAddition& wal) { |
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os << "log_number: " << wal.GetLogNumber() |
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<< " size_in_bytes: " << wal.GetMetadata().GetSizeInBytes(); |
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return os; |
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} |
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std::string WalAddition::DebugString() const { |
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std::ostringstream oss; |
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oss << *this; |
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return oss.str(); |
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} |
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void WalDeletion::EncodeTo(std::string* dst) const { |
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PutVarint64(dst, number_); |
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} |
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Status WalDeletion::DecodeFrom(Slice* src) { |
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constexpr char class_name[] = "WalDeletion"; |
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if (!GetVarint64(src, &number_)) { |
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return Status::Corruption(class_name, "Error decoding WAL log number"); |
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} |
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return Status::OK(); |
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} |
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JSONWriter& operator<<(JSONWriter& jw, const WalDeletion& wal) { |
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jw << "LogNumber" << wal.GetLogNumber(); |
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return jw; |
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} |
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std::ostream& operator<<(std::ostream& os, const WalDeletion& wal) { |
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os << "log_number: " << wal.GetLogNumber(); |
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return os; |
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} |
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std::string WalDeletion::DebugString() const { |
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std::ostringstream oss; |
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oss << *this; |
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return oss.str(); |
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} |
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Status WalSet::AddWal(const WalAddition& wal) { |
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auto it = wals_.lower_bound(wal.GetLogNumber()); |
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if (wal.GetMetadata().HasSize()) { |
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// The WAL must exist without size.
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if (it == wals_.end() || it->first != wal.GetLogNumber()) { |
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std::stringstream ss; |
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ss << "WAL " << wal.GetLogNumber() << " is not created before closing"; |
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return Status::Corruption("WalSet", ss.str()); |
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} |
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if (it->second.HasSize()) { |
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std::stringstream ss; |
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ss << "WAL " << wal.GetLogNumber() << " is closed more than once"; |
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return Status::Corruption("WalSet", ss.str()); |
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} |
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it->second = wal.GetMetadata(); |
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} else { |
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// The WAL must not exist beforehand.
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if (it != wals_.end() && it->first == wal.GetLogNumber()) { |
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std::stringstream ss; |
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ss << "WAL " << wal.GetLogNumber() << " is created more than once"; |
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return Status::Corruption("WalSet", ss.str()); |
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} |
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wals_[wal.GetLogNumber()] = wal.GetMetadata(); |
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} |
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return Status::OK(); |
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} |
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Status WalSet::AddWals(const WalAdditions& wals) { |
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Status s; |
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for (const WalAddition& wal : wals) { |
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s = AddWal(wal); |
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if (!s.ok()) { |
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break; |
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} |
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} |
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return s; |
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} |
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Status WalSet::DeleteWal(const WalDeletion& wal) { |
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auto it = wals_.lower_bound(wal.GetLogNumber()); |
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// The WAL must exist and has been closed.
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if (it == wals_.end() || it->first != wal.GetLogNumber()) { |
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std::stringstream ss; |
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ss << "WAL " << wal.GetLogNumber() << " must exist before deletion"; |
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return Status::Corruption("WalSet", ss.str()); |
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} |
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if (!it->second.HasSize()) { |
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std::stringstream ss; |
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ss << "WAL " << wal.GetLogNumber() << " must be closed before deletion"; |
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return Status::Corruption("WalSet", ss.str()); |
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} |
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wals_.erase(it); |
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return Status::OK(); |
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} |
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Status WalSet::DeleteWals(const WalDeletions& wals) { |
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Status s; |
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for (const WalDeletion& wal : wals) { |
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s = DeleteWal(wal); |
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if (!s.ok()) { |
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break; |
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} |
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} |
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return s; |
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} |
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void WalSet::Reset() { wals_.clear(); } |
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} // namespace ROCKSDB_NAMESPACE
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// 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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// WAL related classes used in VersionEdit and VersionSet.
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#pragma once |
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#include <map> |
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#include <ostream> |
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#include <string> |
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#include <vector> |
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#include "logging/event_logger.h" |
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#include "rocksdb/rocksdb_namespace.h" |
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namespace ROCKSDB_NAMESPACE { |
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class JSONWriter; |
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class Slice; |
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class Status; |
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using WalNumber = uint64_t; |
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// Metadata of a WAL.
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class WalMetadata { |
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public: |
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WalMetadata() = default; |
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explicit WalMetadata(uint64_t size_bytes) : size_bytes_(size_bytes) {} |
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bool HasSize() const { return size_bytes_ != kUnknownWalSize; } |
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void SetSizeInBytes(uint64_t bytes) { size_bytes_ = bytes; } |
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uint64_t GetSizeInBytes() const { return size_bytes_; } |
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private: |
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// The size of WAL is unknown, used when the WAL is not closed yet.
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constexpr static uint64_t kUnknownWalSize = 0; |
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// Size of a closed WAL in bytes.
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uint64_t size_bytes_ = kUnknownWalSize; |
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}; |
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// These tags are persisted to MANIFEST, so it's part of the user API.
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enum class WalAdditionTag : uint32_t { |
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// Indicates that there are no more tags.
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kTerminate = 1, |
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// Size in bytes.
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kSize = 2, |
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// Add tags in the future, such as checksum?
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}; |
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// Records the event of adding a WAL in VersionEdit.
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class WalAddition { |
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public: |
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WalAddition() : number_(0), metadata_() {} |
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explicit WalAddition(WalNumber number) : number_(number), metadata_() {} |
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WalAddition(WalNumber number, WalMetadata meta) |
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: number_(number), metadata_(std::move(meta)) {} |
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WalNumber GetLogNumber() const { return number_; } |
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const WalMetadata& GetMetadata() const { return metadata_; } |
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void EncodeTo(std::string* dst) const; |
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Status DecodeFrom(Slice* src); |
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std::string DebugString() const; |
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private: |
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WalNumber number_; |
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WalMetadata metadata_; |
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}; |
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std::ostream& operator<<(std::ostream& os, const WalAddition& wal); |
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JSONWriter& operator<<(JSONWriter& jw, const WalAddition& wal); |
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using WalAdditions = std::vector<WalAddition>; |
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// Records the event of deleting/archiving a WAL in VersionEdit.
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class WalDeletion { |
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public: |
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WalDeletion() : number_(0) {} |
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explicit WalDeletion(WalNumber number) : number_(number) {} |
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WalNumber GetLogNumber() const { return number_; } |
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void EncodeTo(std::string* dst) const; |
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Status DecodeFrom(Slice* src); |
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std::string DebugString() const; |
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private: |
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WalNumber number_; |
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}; |
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std::ostream& operator<<(std::ostream& os, const WalDeletion& wal); |
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JSONWriter& operator<<(JSONWriter& jw, const WalDeletion& wal); |
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using WalDeletions = std::vector<WalDeletion>; |
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// Used in VersionSet to keep the current set of WALs.
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//
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// When a WAL is created, closed, deleted, or archived,
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// a VersionEdit is logged to MANIFEST and
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// the WAL is added to or deleted from WalSet.
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//
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// Not thread safe, needs external synchronization such as holding DB mutex.
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class WalSet { |
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public: |
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// Add WAL(s).
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// If the WAL has size, it means the WAL is closed,
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// then there must be an existing WAL without size that is added
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// when creating the WAL, otherwise, return Status::Corruption.
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// Can happen when applying a VersionEdit or recovering from MANIFEST.
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Status AddWal(const WalAddition& wal); |
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Status AddWals(const WalAdditions& wals); |
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// Delete WAL(s).
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// The WAL to be deleted must exist, otherwise,
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// return Status::Corruption.
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// Can happen when applying a VersionEdit or recovering from MANIFEST.
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Status DeleteWal(const WalDeletion& wal); |
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Status DeleteWals(const WalDeletions& wals); |
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// Resets the internal state.
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void Reset(); |
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const std::map<WalNumber, WalMetadata>& GetWals() const { return wals_; } |
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private: |
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std::map<WalNumber, WalMetadata> wals_; |
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}; |
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} // namespace ROCKSDB_NAMESPACE
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@ -0,0 +1,127 @@ |
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// 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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#include "db/wal_edit.h" |
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#include "port/port.h" |
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#include "port/stack_trace.h" |
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#include "test_util/testharness.h" |
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#include "test_util/testutil.h" |
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namespace ROCKSDB_NAMESPACE { |
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TEST(WalSet, AddDeleteReset) { |
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WalSet wals; |
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ASSERT_TRUE(wals.GetWals().empty()); |
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// Create WAL 1 - 10.
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for (WalNumber log_number = 1; log_number <= 10; log_number++) { |
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wals.AddWal(WalAddition(log_number)); |
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} |
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ASSERT_EQ(wals.GetWals().size(), 10); |
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// Close WAL 1 - 5.
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for (WalNumber log_number = 1; log_number <= 5; log_number++) { |
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wals.AddWal(WalAddition(log_number, WalMetadata(100))); |
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} |
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ASSERT_EQ(wals.GetWals().size(), 10); |
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// Delete WAL 1 - 5.
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for (WalNumber log_number = 1; log_number <= 5; log_number++) { |
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wals.DeleteWal(WalDeletion(log_number)); |
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} |
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ASSERT_EQ(wals.GetWals().size(), 5); |
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WalNumber expected_log_number = 6; |
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for (auto it : wals.GetWals()) { |
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WalNumber log_number = it.first; |
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ASSERT_EQ(log_number, expected_log_number++); |
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} |
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wals.Reset(); |
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ASSERT_TRUE(wals.GetWals().empty()); |
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} |
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TEST(WalSet, Overwrite) { |
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constexpr WalNumber kNumber = 100; |
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constexpr uint64_t kBytes = 200; |
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WalSet wals; |
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wals.AddWal(WalAddition(kNumber)); |
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ASSERT_FALSE(wals.GetWals().at(kNumber).HasSize()); |
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wals.AddWal(WalAddition(kNumber, WalMetadata(kBytes))); |
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ASSERT_TRUE(wals.GetWals().at(kNumber).HasSize()); |
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ASSERT_EQ(wals.GetWals().at(kNumber).GetSizeInBytes(), kBytes); |
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} |
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TEST(WalSet, CreateTwice) { |
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constexpr WalNumber kNumber = 100; |
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WalSet wals; |
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ASSERT_OK(wals.AddWal(WalAddition(kNumber))); |
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Status s = wals.AddWal(WalAddition(kNumber)); |
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ASSERT_TRUE(s.IsCorruption()); |
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ASSERT_TRUE(s.ToString().find("WAL 100 is created more than once") != |
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std::string::npos); |
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} |
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TEST(WalSet, CloseTwice) { |
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constexpr WalNumber kNumber = 100; |
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constexpr uint64_t kBytes = 200; |
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WalSet wals; |
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ASSERT_OK(wals.AddWal(WalAddition(kNumber))); |
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ASSERT_OK(wals.AddWal(WalAddition(kNumber, WalMetadata(kBytes)))); |
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Status s = wals.AddWal(WalAddition(kNumber, WalMetadata(kBytes))); |
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ASSERT_TRUE(s.IsCorruption()); |
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ASSERT_TRUE(s.ToString().find("WAL 100 is closed more than once") != |
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std::string::npos); |
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} |
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TEST(WalSet, CloseBeforeCreate) { |
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constexpr WalNumber kNumber = 100; |
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constexpr uint64_t kBytes = 200; |
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WalSet wals; |
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Status s = wals.AddWal(WalAddition(kNumber, WalMetadata(kBytes))); |
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ASSERT_TRUE(s.IsCorruption()); |
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ASSERT_TRUE(s.ToString().find("WAL 100 is not created before closing") != |
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std::string::npos); |
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} |
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TEST(WalSet, CreateAfterClose) { |
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constexpr WalNumber kNumber = 100; |
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constexpr uint64_t kBytes = 200; |
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WalSet wals; |
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ASSERT_OK(wals.AddWal(WalAddition(kNumber))); |
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ASSERT_OK(wals.AddWal(WalAddition(kNumber, WalMetadata(kBytes)))); |
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Status s = wals.AddWal(WalAddition(kNumber)); |
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ASSERT_TRUE(s.IsCorruption()); |
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ASSERT_TRUE(s.ToString().find("WAL 100 is created more than once") != |
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std::string::npos); |
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} |
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TEST(WalSet, DeleteNonExistingWal) { |
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constexpr WalNumber kNonExistingNumber = 100; |
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WalSet wals; |
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Status s = wals.DeleteWal(WalDeletion(kNonExistingNumber)); |
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ASSERT_TRUE(s.IsCorruption()); |
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ASSERT_TRUE(s.ToString().find("WAL 100 must exist before deletion") != |
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std::string::npos); |
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} |
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TEST(WalSet, DeleteNonClosedWal) { |
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constexpr WalNumber kNonExistingNumber = 100; |
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WalSet wals; |
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ASSERT_OK(wals.AddWal(WalAddition(kNonExistingNumber))); |
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Status s = wals.DeleteWal(WalDeletion(kNonExistingNumber)); |
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ASSERT_TRUE(s.IsCorruption()); |
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ASSERT_TRUE(s.ToString().find("WAL 100 must be closed before deletion") != |
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std::string::npos); |
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} |
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} // namespace ROCKSDB_NAMESPACE
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int main(int argc, char** argv) { |
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ROCKSDB_NAMESPACE::port::InstallStackTraceHandler(); |
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::testing::InitGoogleTest(&argc, argv); |
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return RUN_ALL_TESTS(); |
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} |
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