Summary: The sequence number was not properly advanced after a rollback marker. The patch extends the existing unit tests to detect the bug and also fixes it. Closes https://github.com/facebook/rocksdb/pull/3157 Differential Revision: D6304291 Pulled By: maysamyabandeh fbshipit-source-id: 1b519c44a5371b802da49c9e32bd00087a8da401
521 lines
22 KiB
C++
521 lines
22 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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#ifndef ROCKSDB_LITE
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#ifndef __STDC_FORMAT_MACROS
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#define __STDC_FORMAT_MACROS
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#endif
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#include "utilities/transactions/write_prepared_txn_db.h"
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#include <inttypes.h>
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#include <string>
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#include <unordered_set>
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#include <vector>
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#include "db/db_impl.h"
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#include "rocksdb/db.h"
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#include "rocksdb/options.h"
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#include "rocksdb/utilities/transaction_db.h"
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#include "util/mutexlock.h"
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#include "util/sync_point.h"
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#include "utilities/transactions/pessimistic_transaction.h"
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#include "utilities/transactions/transaction_db_mutex_impl.h"
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namespace rocksdb {
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Status WritePreparedTxnDB::Initialize(
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const std::vector<size_t>& compaction_enabled_cf_indices,
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const std::vector<ColumnFamilyHandle*>& handles) {
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auto dbimpl = reinterpret_cast<DBImpl*>(GetRootDB());
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assert(dbimpl != nullptr);
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auto rtxns = dbimpl->recovered_transactions();
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for (auto rtxn : rtxns) {
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AddPrepared(rtxn.second->seq_);
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}
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SequenceNumber prev_max = max_evicted_seq_;
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SequenceNumber last_seq = db_impl_->GetLatestSequenceNumber();
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AdvanceMaxEvictedSeq(prev_max, last_seq);
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db_impl_->SetSnapshotChecker(new WritePreparedSnapshotChecker(this));
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auto s = PessimisticTransactionDB::Initialize(compaction_enabled_cf_indices,
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handles);
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return s;
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}
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Transaction* WritePreparedTxnDB::BeginTransaction(
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const WriteOptions& write_options, const TransactionOptions& txn_options,
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Transaction* old_txn) {
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if (old_txn != nullptr) {
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ReinitializeTransaction(old_txn, write_options, txn_options);
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return old_txn;
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} else {
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return new WritePreparedTxn(this, write_options, txn_options);
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}
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}
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Status WritePreparedTxnDB::Get(const ReadOptions& options,
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ColumnFamilyHandle* column_family,
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const Slice& key, PinnableSlice* value) {
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// We are fine with the latest committed value. This could be done by
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// specifying the snapshot as kMaxSequenceNumber.
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SequenceNumber seq = kMaxSequenceNumber;
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if (options.snapshot != nullptr) {
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seq = options.snapshot->GetSequenceNumber();
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}
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WritePreparedTxnReadCallback callback(this, seq);
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bool* dont_care = nullptr;
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// Note: no need to specify a snapshot for read options as no specific
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// snapshot is requested by the user.
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return db_impl_->GetImpl(options, column_family, key, value, dont_care,
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&callback);
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}
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// Struct to hold ownership of snapshot and read callback for iterator cleanup.
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struct WritePreparedTxnDB::IteratorState {
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IteratorState(WritePreparedTxnDB* txn_db, SequenceNumber sequence,
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std::shared_ptr<ManagedSnapshot> s)
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: callback(txn_db, sequence), snapshot(s) {}
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WritePreparedTxnReadCallback callback;
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std::shared_ptr<ManagedSnapshot> snapshot;
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};
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namespace {
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static void CleanupWritePreparedTxnDBIterator(void* arg1, void* arg2) {
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delete reinterpret_cast<WritePreparedTxnDB::IteratorState*>(arg1);
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}
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} // anonymous namespace
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Iterator* WritePreparedTxnDB::NewIterator(const ReadOptions& options,
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ColumnFamilyHandle* column_family) {
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std::shared_ptr<ManagedSnapshot> own_snapshot = nullptr;
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SequenceNumber snapshot_seq = kMaxSequenceNumber;
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if (options.snapshot != nullptr) {
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snapshot_seq = options.snapshot->GetSequenceNumber();
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} else {
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auto* snapshot = db_impl_->GetSnapshot();
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// We take a snapshot to make sure that the related data in the commit map
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// are not deleted.
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snapshot_seq = snapshot->GetSequenceNumber();
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own_snapshot = std::make_shared<ManagedSnapshot>(db_impl_, snapshot);
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}
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assert(snapshot_seq != kMaxSequenceNumber);
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auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
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auto* state = new IteratorState(this, snapshot_seq, own_snapshot);
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auto* db_iter =
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db_impl_->NewIteratorImpl(options, cfd, snapshot_seq, &state->callback);
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db_iter->RegisterCleanup(CleanupWritePreparedTxnDBIterator, state, nullptr);
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return db_iter;
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}
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Status WritePreparedTxnDB::NewIterators(
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const ReadOptions& options,
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const std::vector<ColumnFamilyHandle*>& column_families,
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std::vector<Iterator*>* iterators) {
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std::shared_ptr<ManagedSnapshot> own_snapshot = nullptr;
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SequenceNumber snapshot_seq = kMaxSequenceNumber;
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if (options.snapshot != nullptr) {
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snapshot_seq = options.snapshot->GetSequenceNumber();
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} else {
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auto* snapshot = db_impl_->GetSnapshot();
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// We take a snapshot to make sure that the related data in the commit map
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// are not deleted.
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snapshot_seq = snapshot->GetSequenceNumber();
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own_snapshot = std::make_shared<ManagedSnapshot>(db_impl_, snapshot);
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}
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iterators->clear();
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iterators->reserve(column_families.size());
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for (auto* column_family : column_families) {
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auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
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auto* state = new IteratorState(this, snapshot_seq, own_snapshot);
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auto* db_iter =
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db_impl_->NewIteratorImpl(options, cfd, snapshot_seq, &state->callback);
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db_iter->RegisterCleanup(CleanupWritePreparedTxnDBIterator, state, nullptr);
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iterators->push_back(db_iter);
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}
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return Status::OK();
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}
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void WritePreparedTxnDB::Init(const TransactionDBOptions& /* unused */) {
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// Adcance max_evicted_seq_ no more than 100 times before the cache wraps
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// around.
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INC_STEP_FOR_MAX_EVICTED =
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std::max(SNAPSHOT_CACHE_SIZE / 100, static_cast<size_t>(1));
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snapshot_cache_ = unique_ptr<std::atomic<SequenceNumber>[]>(
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new std::atomic<SequenceNumber>[SNAPSHOT_CACHE_SIZE] {});
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commit_cache_ = unique_ptr<std::atomic<CommitEntry64b>[]>(
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new std::atomic<CommitEntry64b>[COMMIT_CACHE_SIZE] {});
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}
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// Returns true if commit_seq <= snapshot_seq
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bool WritePreparedTxnDB::IsInSnapshot(uint64_t prep_seq,
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uint64_t snapshot_seq) const {
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// Here we try to infer the return value without looking into prepare list.
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// This would help avoiding synchronization over a shared map.
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// TODO(myabandeh): read your own writes
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// TODO(myabandeh): optimize this. This sequence of checks must be correct but
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// not necessary efficient
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if (prep_seq == 0) {
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// Compaction will output keys to bottom-level with sequence number 0 if
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// it is visible to the earliest snapshot.
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return true;
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}
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if (snapshot_seq < prep_seq) {
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// snapshot_seq < prep_seq <= commit_seq => snapshot_seq < commit_seq
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return false;
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}
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if (!delayed_prepared_empty_.load(std::memory_order_acquire)) {
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// We should not normally reach here
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ReadLock rl(&prepared_mutex_);
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if (delayed_prepared_.find(prep_seq) != delayed_prepared_.end()) {
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// Then it is not committed yet
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return false;
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}
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}
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auto indexed_seq = prep_seq % COMMIT_CACHE_SIZE;
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CommitEntry64b dont_care;
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CommitEntry cached;
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bool exist = GetCommitEntry(indexed_seq, &dont_care, &cached);
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if (exist && prep_seq == cached.prep_seq) {
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// It is committed and also not evicted from commit cache
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return cached.commit_seq <= snapshot_seq;
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}
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// else it could be committed but not inserted in the map which could happen
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// after recovery, or it could be committed and evicted by another commit, or
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// never committed.
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// At this point we dont know if it was committed or it is still prepared
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auto max_evicted_seq = max_evicted_seq_.load(std::memory_order_acquire);
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if (max_evicted_seq < prep_seq) {
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// Not evicted from cache and also not present, so must be still prepared
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return false;
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}
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// When advancing max_evicted_seq_, we move older entires from prepared to
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// delayed_prepared_. Also we move evicted entries from commit cache to
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// old_commit_map_ if it overlaps with any snapshot. Since prep_seq <=
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// max_evicted_seq_, we have three cases: i) in delayed_prepared_, ii) in
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// old_commit_map_, iii) committed with no conflict with any snapshot (i)
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// delayed_prepared_ is checked above
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if (max_evicted_seq < snapshot_seq) { // then (ii) cannot be the case
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// only (iii) is the case: committed
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// commit_seq <= max_evicted_seq_ < snapshot_seq => commit_seq <
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// snapshot_seq
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return true;
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}
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// else (ii) might be the case: check the commit data saved for this snapshot.
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// If there was no overlapping commit entry, then it is committed with a
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// commit_seq lower than any live snapshot, including snapshot_seq.
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if (old_commit_map_empty_.load(std::memory_order_acquire)) {
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return true;
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}
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{
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// We should not normally reach here
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// TODO(myabandeh): check only if snapshot_seq is in the list of snaphots
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ReadLock rl(&old_commit_map_mutex_);
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auto old_commit_entry = old_commit_map_.find(prep_seq);
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if (old_commit_entry == old_commit_map_.end() ||
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old_commit_entry->second <= snapshot_seq) {
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return true;
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}
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}
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// (ii) it the case: it is committed but after the snapshot_seq
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return false;
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}
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void WritePreparedTxnDB::AddPrepared(uint64_t seq) {
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ROCKS_LOG_DEBUG(info_log_, "Txn %" PRIu64 " Prepareing", seq);
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// TODO(myabandeh): Add a runtime check to ensure the following assert.
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assert(seq > max_evicted_seq_);
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WriteLock wl(&prepared_mutex_);
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prepared_txns_.push(seq);
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}
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void WritePreparedTxnDB::RollbackPrepared(uint64_t prep_seq,
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uint64_t rollback_seq) {
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ROCKS_LOG_DEBUG(
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info_log_, "Txn %" PRIu64 " rolling back with rollback seq of " PRIu64 "",
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prep_seq, rollback_seq);
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std::vector<SequenceNumber> snapshots =
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GetSnapshotListFromDB(kMaxSequenceNumber);
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// TODO(myabandeh): currently we are assuming that there is no snapshot taken
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// when a transaciton is rolled back. This is the case the way MySQL does
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// rollback which is after recovery. We should extend it to be able to
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// rollback txns that overlap with exsiting snapshots.
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assert(snapshots.size() == 0);
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if (snapshots.size()) {
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throw std::runtime_error(
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"Rollback reqeust while there are live snapshots.");
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}
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WriteLock wl(&prepared_mutex_);
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prepared_txns_.erase(prep_seq);
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bool was_empty = delayed_prepared_.empty();
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if (!was_empty) {
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delayed_prepared_.erase(prep_seq);
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bool is_empty = delayed_prepared_.empty();
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if (was_empty != is_empty) {
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delayed_prepared_empty_.store(is_empty, std::memory_order_release);
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}
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}
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}
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void WritePreparedTxnDB::AddCommitted(uint64_t prepare_seq,
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uint64_t commit_seq) {
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ROCKS_LOG_DEBUG(info_log_, "Txn %" PRIu64 " Committing with %" PRIu64,
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prepare_seq, commit_seq);
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auto indexed_seq = prepare_seq % COMMIT_CACHE_SIZE;
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CommitEntry64b evicted_64b;
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CommitEntry evicted;
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bool to_be_evicted = GetCommitEntry(indexed_seq, &evicted_64b, &evicted);
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if (to_be_evicted) {
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auto prev_max = max_evicted_seq_.load(std::memory_order_acquire);
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if (prev_max < evicted.commit_seq) {
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// Inc max in larger steps to avoid frequent updates
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auto max_evicted_seq = evicted.commit_seq + INC_STEP_FOR_MAX_EVICTED;
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AdvanceMaxEvictedSeq(prev_max, max_evicted_seq);
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}
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// After each eviction from commit cache, check if the commit entry should
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// be kept around because it overlaps with a live snapshot.
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CheckAgainstSnapshots(evicted);
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}
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bool succ =
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ExchangeCommitEntry(indexed_seq, evicted_64b, {prepare_seq, commit_seq});
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if (!succ) {
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// A very rare event, in which the commit entry is updated before we do.
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// Here we apply a very simple solution of retrying.
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// TODO(myabandeh): do precautions to detect bugs that cause infinite loops
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AddCommitted(prepare_seq, commit_seq);
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return;
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}
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{
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WriteLock wl(&prepared_mutex_);
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prepared_txns_.erase(prepare_seq);
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bool was_empty = delayed_prepared_.empty();
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if (!was_empty) {
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delayed_prepared_.erase(prepare_seq);
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bool is_empty = delayed_prepared_.empty();
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if (was_empty != is_empty) {
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delayed_prepared_empty_.store(is_empty, std::memory_order_release);
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}
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}
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}
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}
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bool WritePreparedTxnDB::GetCommitEntry(const uint64_t indexed_seq,
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CommitEntry64b* entry_64b,
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CommitEntry* entry) const {
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*entry_64b = commit_cache_[indexed_seq].load(std::memory_order_acquire);
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bool valid = entry_64b->Parse(indexed_seq, entry, FORMAT);
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return valid;
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}
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bool WritePreparedTxnDB::AddCommitEntry(const uint64_t indexed_seq,
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const CommitEntry& new_entry,
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CommitEntry* evicted_entry) {
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CommitEntry64b new_entry_64b(new_entry, FORMAT);
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CommitEntry64b evicted_entry_64b = commit_cache_[indexed_seq].exchange(
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new_entry_64b, std::memory_order_acq_rel);
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bool valid = evicted_entry_64b.Parse(indexed_seq, evicted_entry, FORMAT);
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return valid;
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}
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bool WritePreparedTxnDB::ExchangeCommitEntry(const uint64_t indexed_seq,
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CommitEntry64b& expected_entry_64b,
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const CommitEntry& new_entry) {
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auto& atomic_entry = commit_cache_[indexed_seq];
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CommitEntry64b new_entry_64b(new_entry, FORMAT);
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bool succ = atomic_entry.compare_exchange_strong(
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expected_entry_64b, new_entry_64b, std::memory_order_acq_rel,
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std::memory_order_acquire);
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return succ;
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}
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void WritePreparedTxnDB::AdvanceMaxEvictedSeq(SequenceNumber& prev_max,
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SequenceNumber& new_max) {
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// When max_evicted_seq_ advances, move older entries from prepared_txns_
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// to delayed_prepared_. This guarantees that if a seq is lower than max,
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// then it is not in prepared_txns_ ans save an expensive, synchronized
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// lookup from a shared set. delayed_prepared_ is expected to be empty in
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// normal cases.
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{
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WriteLock wl(&prepared_mutex_);
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while (!prepared_txns_.empty() && prepared_txns_.top() <= new_max) {
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auto to_be_popped = prepared_txns_.top();
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delayed_prepared_.insert(to_be_popped);
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prepared_txns_.pop();
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delayed_prepared_empty_.store(false, std::memory_order_release);
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}
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}
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// With each change to max_evicted_seq_ fetch the live snapshots behind it.
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// We use max as the version of snapshots to identify how fresh are the
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// snapshot list. This works because the snapshots are between 0 and
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// max, so the larger the max, the more complete they are.
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SequenceNumber new_snapshots_version = new_max;
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std::vector<SequenceNumber> snapshots;
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bool update_snapshots = false;
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if (new_snapshots_version > snapshots_version_) {
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// This is to avoid updating the snapshots_ if it already updated
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// with a more recent vesion by a concrrent thread
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update_snapshots = true;
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// We only care about snapshots lower then max
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snapshots = GetSnapshotListFromDB(new_max);
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}
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if (update_snapshots) {
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UpdateSnapshots(snapshots, new_snapshots_version);
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}
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while (prev_max < new_max && !max_evicted_seq_.compare_exchange_weak(
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prev_max, new_max, std::memory_order_acq_rel,
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std::memory_order_relaxed)) {
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};
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}
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const std::vector<SequenceNumber> WritePreparedTxnDB::GetSnapshotListFromDB(
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SequenceNumber max) {
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InstrumentedMutex(db_impl_->mutex());
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return db_impl_->snapshots().GetAll(nullptr, max);
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}
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void WritePreparedTxnDB::UpdateSnapshots(
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const std::vector<SequenceNumber>& snapshots,
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const SequenceNumber& version) {
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TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:start");
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TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:start");
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#ifndef NDEBUG
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size_t sync_i = 0;
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#endif
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WriteLock wl(&snapshots_mutex_);
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snapshots_version_ = version;
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// We update the list concurrently with the readers.
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// Both new and old lists are sorted and the new list is subset of the
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// previous list plus some new items. Thus if a snapshot repeats in
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// both new and old lists, it will appear upper in the new list. So if
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// we simply insert the new snapshots in order, if an overwritten item
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// is still valid in the new list is either written to the same place in
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// the array or it is written in a higher palce before it gets
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// overwritten by another item. This guarantess a reader that reads the
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// list bottom-up will eventaully see a snapshot that repeats in the
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// update, either before it gets overwritten by the writer or
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// afterwards.
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size_t i = 0;
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auto it = snapshots.begin();
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for (; it != snapshots.end() && i < SNAPSHOT_CACHE_SIZE; it++, i++) {
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snapshot_cache_[i].store(*it, std::memory_order_release);
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TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:", ++sync_i);
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TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:", sync_i);
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}
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#ifndef NDEBUG
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// Release the remaining sync points since they are useless given that the
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// reader would also use lock to access snapshots
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for (++sync_i; sync_i <= 10; ++sync_i) {
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TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:", sync_i);
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TEST_IDX_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:", sync_i);
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}
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#endif
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snapshots_.clear();
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for (; it != snapshots.end(); it++) {
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// Insert them to a vector that is less efficient to access
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// concurrently
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snapshots_.push_back(*it);
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}
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// Update the size at the end. Otherwise a parallel reader might read
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// items that are not set yet.
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snapshots_total_.store(snapshots.size(), std::memory_order_release);
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TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:p:end");
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TEST_SYNC_POINT("WritePreparedTxnDB::UpdateSnapshots:s:end");
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|
}
|
|
|
|
void WritePreparedTxnDB::CheckAgainstSnapshots(const CommitEntry& evicted) {
|
|
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:start");
|
|
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:start");
|
|
#ifndef NDEBUG
|
|
size_t sync_i = 0;
|
|
#endif
|
|
// First check the snapshot cache that is efficient for concurrent access
|
|
auto cnt = snapshots_total_.load(std::memory_order_acquire);
|
|
// The list might get updated concurrently as we are reading from it. The
|
|
// reader should be able to read all the snapshots that are still valid
|
|
// after the update. Since the survived snapshots are written in a higher
|
|
// place before gets overwritten the reader that reads bottom-up will
|
|
// eventully see it.
|
|
const bool next_is_larger = true;
|
|
SequenceNumber snapshot_seq = kMaxSequenceNumber;
|
|
size_t ip1 = std::min(cnt, SNAPSHOT_CACHE_SIZE);
|
|
for (; 0 < ip1; ip1--) {
|
|
snapshot_seq = snapshot_cache_[ip1 - 1].load(std::memory_order_acquire);
|
|
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:",
|
|
++sync_i);
|
|
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:", sync_i);
|
|
if (!MaybeUpdateOldCommitMap(evicted.prep_seq, evicted.commit_seq,
|
|
snapshot_seq, !next_is_larger)) {
|
|
break;
|
|
}
|
|
}
|
|
#ifndef NDEBUG
|
|
// Release the remaining sync points before accquiring the lock
|
|
for (++sync_i; sync_i <= 10; ++sync_i) {
|
|
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:", sync_i);
|
|
TEST_IDX_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:", sync_i);
|
|
}
|
|
#endif
|
|
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:p:end");
|
|
TEST_SYNC_POINT("WritePreparedTxnDB::CheckAgainstSnapshots:s:end");
|
|
if (UNLIKELY(SNAPSHOT_CACHE_SIZE < cnt && ip1 == SNAPSHOT_CACHE_SIZE &&
|
|
snapshot_seq < evicted.prep_seq)) {
|
|
// Then access the less efficient list of snapshots_
|
|
ReadLock rl(&snapshots_mutex_);
|
|
// Items could have moved from the snapshots_ to snapshot_cache_ before
|
|
// accquiring the lock. To make sure that we do not miss a valid snapshot,
|
|
// read snapshot_cache_ again while holding the lock.
|
|
for (size_t i = 0; i < SNAPSHOT_CACHE_SIZE; i++) {
|
|
snapshot_seq = snapshot_cache_[i].load(std::memory_order_acquire);
|
|
if (!MaybeUpdateOldCommitMap(evicted.prep_seq, evicted.commit_seq,
|
|
snapshot_seq, next_is_larger)) {
|
|
break;
|
|
}
|
|
}
|
|
for (auto snapshot_seq_2 : snapshots_) {
|
|
if (!MaybeUpdateOldCommitMap(evicted.prep_seq, evicted.commit_seq,
|
|
snapshot_seq_2, next_is_larger)) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
bool WritePreparedTxnDB::MaybeUpdateOldCommitMap(
|
|
const uint64_t& prep_seq, const uint64_t& commit_seq,
|
|
const uint64_t& snapshot_seq, const bool next_is_larger = true) {
|
|
// If we do not store an entry in old_commit_map we assume it is committed in
|
|
// all snapshots. if commit_seq <= snapshot_seq, it is considered already in
|
|
// the snapshot so we need not to keep the entry around for this snapshot.
|
|
if (commit_seq <= snapshot_seq) {
|
|
// continue the search if the next snapshot could be smaller than commit_seq
|
|
return !next_is_larger;
|
|
}
|
|
// then snapshot_seq < commit_seq
|
|
if (prep_seq <= snapshot_seq) { // overlapping range
|
|
WriteLock wl(&old_commit_map_mutex_);
|
|
old_commit_map_empty_.store(false, std::memory_order_release);
|
|
old_commit_map_[prep_seq] = commit_seq;
|
|
// Storing once is enough. No need to check it for other snapshots.
|
|
return false;
|
|
}
|
|
// continue the search if the next snapshot could be larger than prep_seq
|
|
return next_is_larger;
|
|
}
|
|
|
|
WritePreparedTxnDB::~WritePreparedTxnDB() {
|
|
// At this point there could be running compaction/flush holding a
|
|
// SnapshotChecker, which holds a pointer back to WritePreparedTxnDB.
|
|
// Make sure those jobs finished before destructing WritePreparedTxnDB.
|
|
db_impl_->CancelAllBackgroundWork(true /*wait*/);
|
|
}
|
|
|
|
} // namespace rocksdb
|
|
#endif // ROCKSDB_LITE
|