Summary: This patch record min log number to keep to the manifest while flushing SST files to ignore them and any WAL older than them during recovery. This is to avoid scenarios when we have a gap between the WAL files are fed to the recovery procedure. The gap could happen by for example out-of-order WAL deletion. Such gap could cause problems in 2PC recovery where the prepared and commit entry are placed into two separate WAL and gap in the WALs could result into not processing the WAL with the commit entry and hence breaking the 2PC recovery logic. Before the commit, for 2PC case, we determined which log number to keep in FindObsoleteFiles(). We looked at the earliest logs with outstanding prepare entries, or prepare entries whose respective commit or abort are in memtable. With the commit, the same calculation is done while we apply the SST flush. Just before installing the flush file, we precompute the earliest log file to keep after the flush finishes using the same logic (but skipping the memtables just flushed), record this information to the manifest entry for this new flushed SST file. This pre-computed value is also remembered in memory, and will later be used to determine whether a log file can be deleted. This value is unlikely to change until next flush because the commit entry will stay in memtable. (In WritePrepared, we could have removed the older log files as soon as all prepared entries are committed. It's not yet done anyway. Even if we do it, the only thing we loss with this new approach is earlier log deletion between two flushes, which does not guarantee to happen anyway because the obsolete file clean-up function is only executed after flush or compaction) This min log number to keep is stored in the manifest using the safely-ignore customized field of AddFile entry, in order to guarantee that the DB generated using newer release can be opened by previous releases no older than 4.2. Closes https://github.com/facebook/rocksdb/pull/3765 Differential Revision: D7747618 Pulled By: siying fbshipit-source-id: d00c92105b4f83852e9754a1b70d6b64cb590729main
Siying Dong
6 years ago
committed by
Facebook Github Bot
parent
cfb86659bf
commit
d59549298f
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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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//
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#include "db/logs_with_prep_tracker.h" |
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#include "port/likely.h" |
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namespace rocksdb { |
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void LogsWithPrepTracker::MarkLogAsHavingPrepSectionFlushed(uint64_t log) { |
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assert(log != 0); |
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std::lock_guard<std::mutex> lock(prepared_section_completed_mutex_); |
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auto it = prepared_section_completed_.find(log); |
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if (UNLIKELY(it == prepared_section_completed_.end())) { |
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prepared_section_completed_[log] = 1; |
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} else { |
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it->second += 1; |
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} |
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} |
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void LogsWithPrepTracker::MarkLogAsContainingPrepSection(uint64_t log) { |
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assert(log != 0); |
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std::lock_guard<std::mutex> lock(logs_with_prep_mutex_); |
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auto rit = logs_with_prep_.rbegin(); |
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bool updated = false; |
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// Most probably the last log is the one that is being marked for
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// having a prepare section; so search from the end.
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for (; rit != logs_with_prep_.rend() && rit->log >= log; ++rit) { |
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if (rit->log == log) { |
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rit->cnt++; |
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updated = true; |
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break; |
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} |
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} |
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if (!updated) { |
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// We are either at the start, or at a position with rit->log < log
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logs_with_prep_.insert(rit.base(), {log, 1}); |
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} |
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} |
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uint64_t LogsWithPrepTracker::FindMinLogContainingOutstandingPrep() { |
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std::lock_guard<std::mutex> lock(logs_with_prep_mutex_); |
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auto it = logs_with_prep_.begin(); |
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// start with the smallest log
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for (; it != logs_with_prep_.end();) { |
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auto min_log = it->log; |
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{ |
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std::lock_guard<std::mutex> lock2(prepared_section_completed_mutex_); |
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auto completed_it = prepared_section_completed_.find(min_log); |
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if (completed_it == prepared_section_completed_.end() || |
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completed_it->second < it->cnt) { |
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return min_log; |
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} |
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assert(completed_it != prepared_section_completed_.end() && |
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completed_it->second == it->cnt); |
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prepared_section_completed_.erase(completed_it); |
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} |
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// erase from beginning in vector is not efficient but this function is not
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// on the fast path.
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it = logs_with_prep_.erase(it); |
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} |
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// no such log found
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return 0; |
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} |
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} // namespace rocksdb
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@ -0,0 +1,61 @@ |
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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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//
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#pragma once |
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#include <stdint.h> |
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#include <cassert> |
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#include <cstdlib> |
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#include <mutex> |
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#include <unordered_map> |
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#include <vector> |
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namespace rocksdb { |
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// This class is used to track the log files with outstanding prepare entries.
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class LogsWithPrepTracker { |
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public: |
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// Called when a transaction prepared in `log` has been committed or aborted.
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void MarkLogAsHavingPrepSectionFlushed(uint64_t log); |
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// Called when a transaction is prepared in `log`.
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void MarkLogAsContainingPrepSection(uint64_t log); |
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// Return the earliest log file with outstanding prepare entries.
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uint64_t FindMinLogContainingOutstandingPrep(); |
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size_t TEST_PreparedSectionCompletedSize() { |
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return prepared_section_completed_.size(); |
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} |
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size_t TEST_LogsWithPrepSize() { return logs_with_prep_.size(); } |
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private: |
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// REQUIRES: logs_with_prep_mutex_ held
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//
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// sorted list of log numbers still containing prepared data.
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// this is used by FindObsoleteFiles to determine which
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// flushed logs we must keep around because they still
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// contain prepared data which has not been committed or rolled back
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struct LogCnt { |
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uint64_t log; // the log number
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uint64_t cnt; // number of prepared sections in the log
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}; |
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std::vector<LogCnt> logs_with_prep_; |
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std::mutex logs_with_prep_mutex_; |
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// REQUIRES: prepared_section_completed_mutex_ held
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//
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// to be used in conjunction with logs_with_prep_.
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// once a transaction with data in log L is committed or rolled back
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// rather than updating logs_with_prep_ directly we keep track of that
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// in prepared_section_completed_ which maps LOG -> instance_count. This helps
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// avoiding contention between a commit thread and the prepare threads.
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//
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// when trying to determine the minimum log still active we first
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// consult logs_with_prep_. while that root value maps to
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// an equal value in prepared_section_completed_ we erase the log from
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// both logs_with_prep_ and prepared_section_completed_.
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std::unordered_map<uint64_t, uint64_t> prepared_section_completed_; |
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std::mutex prepared_section_completed_mutex_; |
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}; |
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} // namespace rocksdb
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