rocksdb/utilities/transactions/pessimistic_transaction.cc
Maysam Yabandeh eb6425303e Update WritePrepared with the pseudo code
Summary:
Implement the main body of WritePrepared pseudo code. This includes PrepareInternal and CommitInternal, as well as AddCommitted which updates the commit map. It also provides a IsInSnapshot method that could be later called form the read path to decide if a version is in the read snapshot or it should other be skipped.

This patch lacks unit tests and does not attempt to offer an efficient implementation. The idea is that to have the API specified so that we can work on related tasks in parallel.
Closes https://github.com/facebook/rocksdb/pull/2713

Differential Revision: D5640021

Pulled By: maysamyabandeh

fbshipit-source-id: bfa7a05e8d8498811fab714ce4b9c21530514e1c
2017-08-16 16:57:47 -07:00

596 lines
19 KiB
C++

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#ifndef ROCKSDB_LITE
#include "utilities/transactions/pessimistic_transaction.h"
#include <map>
#include <set>
#include <string>
#include <vector>
#include "db/column_family.h"
#include "db/db_impl.h"
#include "rocksdb/comparator.h"
#include "rocksdb/db.h"
#include "rocksdb/snapshot.h"
#include "rocksdb/status.h"
#include "rocksdb/utilities/transaction_db.h"
#include "util/cast_util.h"
#include "util/string_util.h"
#include "util/sync_point.h"
#include "utilities/transactions/pessimistic_transaction_db.h"
#include "utilities/transactions/transaction_util.h"
namespace rocksdb {
struct WriteOptions;
std::atomic<TransactionID> PessimisticTransaction::txn_id_counter_(1);
TransactionID PessimisticTransaction::GenTxnID() {
return txn_id_counter_.fetch_add(1);
}
PessimisticTransaction::PessimisticTransaction(
TransactionDB* txn_db, const WriteOptions& write_options,
const TransactionOptions& txn_options)
: TransactionBaseImpl(txn_db->GetRootDB(), write_options),
txn_db_impl_(nullptr),
expiration_time_(0),
txn_id_(0),
waiting_cf_id_(0),
waiting_key_(nullptr),
lock_timeout_(0),
deadlock_detect_(false),
deadlock_detect_depth_(0) {
txn_db_impl_ =
static_cast_with_check<PessimisticTransactionDB, TransactionDB>(txn_db);
db_impl_ = static_cast_with_check<DBImpl, DB>(db_);
Initialize(txn_options);
}
void PessimisticTransaction::Initialize(const TransactionOptions& txn_options) {
txn_id_ = GenTxnID();
txn_state_ = STARTED;
deadlock_detect_ = txn_options.deadlock_detect;
deadlock_detect_depth_ = txn_options.deadlock_detect_depth;
write_batch_.SetMaxBytes(txn_options.max_write_batch_size);
lock_timeout_ = txn_options.lock_timeout * 1000;
if (lock_timeout_ < 0) {
// Lock timeout not set, use default
lock_timeout_ =
txn_db_impl_->GetTxnDBOptions().transaction_lock_timeout * 1000;
}
if (txn_options.expiration >= 0) {
expiration_time_ = start_time_ + txn_options.expiration * 1000;
} else {
expiration_time_ = 0;
}
if (txn_options.set_snapshot) {
SetSnapshot();
}
if (expiration_time_ > 0) {
txn_db_impl_->InsertExpirableTransaction(txn_id_, this);
}
}
PessimisticTransaction::~PessimisticTransaction() {
txn_db_impl_->UnLock(this, &GetTrackedKeys());
if (expiration_time_ > 0) {
txn_db_impl_->RemoveExpirableTransaction(txn_id_);
}
if (!name_.empty() && txn_state_ != COMMITED) {
txn_db_impl_->UnregisterTransaction(this);
}
}
void PessimisticTransaction::Clear() {
txn_db_impl_->UnLock(this, &GetTrackedKeys());
TransactionBaseImpl::Clear();
}
void PessimisticTransaction::Reinitialize(
TransactionDB* txn_db, const WriteOptions& write_options,
const TransactionOptions& txn_options) {
if (!name_.empty() && txn_state_ != COMMITED) {
txn_db_impl_->UnregisterTransaction(this);
}
TransactionBaseImpl::Reinitialize(txn_db->GetRootDB(), write_options);
Initialize(txn_options);
}
bool PessimisticTransaction::IsExpired() const {
if (expiration_time_ > 0) {
if (db_->GetEnv()->NowMicros() >= expiration_time_) {
// Transaction is expired.
return true;
}
}
return false;
}
WriteCommittedTxn::WriteCommittedTxn(TransactionDB* txn_db,
const WriteOptions& write_options,
const TransactionOptions& txn_options)
: PessimisticTransaction(txn_db, write_options, txn_options){};
Status WriteCommittedTxn::CommitBatch(WriteBatch* batch) {
TransactionKeyMap keys_to_unlock;
Status s = LockBatch(batch, &keys_to_unlock);
if (!s.ok()) {
return s;
}
bool can_commit = false;
if (IsExpired()) {
s = Status::Expired();
} else if (expiration_time_ > 0) {
TransactionState expected = STARTED;
can_commit = std::atomic_compare_exchange_strong(&txn_state_, &expected,
AWAITING_COMMIT);
} else if (txn_state_ == STARTED) {
// lock stealing is not a concern
can_commit = true;
}
if (can_commit) {
txn_state_.store(AWAITING_COMMIT);
s = db_->Write(write_options_, batch);
if (s.ok()) {
txn_state_.store(COMMITED);
}
} else if (txn_state_ == LOCKS_STOLEN) {
s = Status::Expired();
} else {
s = Status::InvalidArgument("Transaction is not in state for commit.");
}
txn_db_impl_->UnLock(this, &keys_to_unlock);
return s;
}
Status PessimisticTransaction::Prepare() {
Status s;
if (name_.empty()) {
return Status::InvalidArgument(
"Cannot prepare a transaction that has not been named.");
}
if (IsExpired()) {
return Status::Expired();
}
bool can_prepare = false;
if (expiration_time_ > 0) {
// must concern ourselves with expiraton and/or lock stealing
// need to compare/exchange bc locks could be stolen under us here
TransactionState expected = STARTED;
can_prepare = std::atomic_compare_exchange_strong(&txn_state_, &expected,
AWAITING_PREPARE);
} else if (txn_state_ == STARTED) {
// expiration and lock stealing is not possible
can_prepare = true;
}
if (can_prepare) {
txn_state_.store(AWAITING_PREPARE);
// transaction can't expire after preparation
expiration_time_ = 0;
s = PrepareInternal();
if (s.ok()) {
assert(log_number_ != 0);
dbimpl_->MarkLogAsContainingPrepSection(log_number_);
txn_state_.store(PREPARED);
}
} else if (txn_state_ == LOCKS_STOLEN) {
s = Status::Expired();
} else if (txn_state_ == PREPARED) {
s = Status::InvalidArgument("Transaction has already been prepared.");
} else if (txn_state_ == COMMITED) {
s = Status::InvalidArgument("Transaction has already been committed.");
} else if (txn_state_ == ROLLEDBACK) {
s = Status::InvalidArgument("Transaction has already been rolledback.");
} else {
s = Status::InvalidArgument("Transaction is not in state for commit.");
}
return s;
}
Status WriteCommittedTxn::PrepareInternal() {
WriteOptions write_options = write_options_;
write_options.disableWAL = false;
WriteBatchInternal::MarkEndPrepare(GetWriteBatch()->GetWriteBatch(), name_);
Status s =
db_impl_->WriteImpl(write_options, GetWriteBatch()->GetWriteBatch(),
/*callback*/ nullptr, &log_number_, /*log ref*/ 0,
/* disable_memtable*/ true);
return s;
}
Status PessimisticTransaction::Commit() {
Status s;
bool commit_without_prepare = false;
bool commit_prepared = false;
if (IsExpired()) {
return Status::Expired();
}
if (expiration_time_ > 0) {
// we must atomicaly compare and exchange the state here because at
// this state in the transaction it is possible for another thread
// to change our state out from under us in the even that we expire and have
// our locks stolen. In this case the only valid state is STARTED because
// a state of PREPARED would have a cleared expiration_time_.
TransactionState expected = STARTED;
commit_without_prepare = std::atomic_compare_exchange_strong(
&txn_state_, &expected, AWAITING_COMMIT);
TEST_SYNC_POINT("TransactionTest::ExpirableTransactionDataRace:1");
} else if (txn_state_ == PREPARED) {
// expiration and lock stealing is not a concern
commit_prepared = true;
} else if (txn_state_ == STARTED) {
// expiration and lock stealing is not a concern
commit_without_prepare = true;
// TODO(myabandeh): what if the user mistakenly forgets prepare? We should
// add an option so that the user explictly express the intention of
// skipping the prepare phase.
}
if (commit_without_prepare) {
assert(!commit_prepared);
if (WriteBatchInternal::Count(GetCommitTimeWriteBatch()) > 0) {
s = Status::InvalidArgument(
"Commit-time batch contains values that will not be committed.");
} else {
txn_state_.store(AWAITING_COMMIT);
s = CommitWithoutPrepareInternal();
Clear();
if (s.ok()) {
txn_state_.store(COMMITED);
}
}
} else if (commit_prepared) {
txn_state_.store(AWAITING_COMMIT);
s = CommitInternal();
if (!s.ok()) {
ROCKS_LOG_WARN(db_impl_->immutable_db_options().info_log,
"Commit write failed");
return s;
}
// FindObsoleteFiles must now look to the memtables
// to determine what prep logs must be kept around,
// not the prep section heap.
assert(log_number_ > 0);
dbimpl_->MarkLogAsHavingPrepSectionFlushed(log_number_);
txn_db_impl_->UnregisterTransaction(this);
Clear();
txn_state_.store(COMMITED);
} else if (txn_state_ == LOCKS_STOLEN) {
s = Status::Expired();
} else if (txn_state_ == COMMITED) {
s = Status::InvalidArgument("Transaction has already been committed.");
} else if (txn_state_ == ROLLEDBACK) {
s = Status::InvalidArgument("Transaction has already been rolledback.");
} else {
s = Status::InvalidArgument("Transaction is not in state for commit.");
}
return s;
}
Status WriteCommittedTxn::CommitWithoutPrepareInternal() {
Status s = db_->Write(write_options_, GetWriteBatch()->GetWriteBatch());
return s;
}
Status WriteCommittedTxn::CommitInternal() {
// We take the commit-time batch and append the Commit marker.
// The Memtable will ignore the Commit marker in non-recovery mode
WriteBatch* working_batch = GetCommitTimeWriteBatch();
WriteBatchInternal::MarkCommit(working_batch, name_);
// any operations appended to this working_batch will be ignored from WAL
working_batch->MarkWalTerminationPoint();
// insert prepared batch into Memtable only skipping WAL.
// Memtable will ignore BeginPrepare/EndPrepare markers
// in non recovery mode and simply insert the values
WriteBatchInternal::Append(working_batch, GetWriteBatch()->GetWriteBatch());
auto s = db_impl_->WriteImpl(write_options_, working_batch, nullptr, nullptr,
log_number_);
return s;
}
Status WriteCommittedTxn::Rollback() {
Status s;
if (txn_state_ == PREPARED) {
WriteBatch rollback_marker;
WriteBatchInternal::MarkRollback(&rollback_marker, name_);
txn_state_.store(AWAITING_ROLLBACK);
s = db_impl_->WriteImpl(write_options_, &rollback_marker);
if (s.ok()) {
// we do not need to keep our prepared section around
assert(log_number_ > 0);
dbimpl_->MarkLogAsHavingPrepSectionFlushed(log_number_);
Clear();
txn_state_.store(ROLLEDBACK);
}
} else if (txn_state_ == STARTED) {
// prepare couldn't have taken place
Clear();
} else if (txn_state_ == COMMITED) {
s = Status::InvalidArgument("This transaction has already been committed.");
} else {
s = Status::InvalidArgument(
"Two phase transaction is not in state for rollback.");
}
return s;
}
Status PessimisticTransaction::RollbackToSavePoint() {
if (txn_state_ != STARTED) {
return Status::InvalidArgument("Transaction is beyond state for rollback.");
}
// Unlock any keys locked since last transaction
const std::unique_ptr<TransactionKeyMap>& keys =
GetTrackedKeysSinceSavePoint();
if (keys) {
txn_db_impl_->UnLock(this, keys.get());
}
return TransactionBaseImpl::RollbackToSavePoint();
}
// Lock all keys in this batch.
// On success, caller should unlock keys_to_unlock
Status PessimisticTransaction::LockBatch(WriteBatch* batch,
TransactionKeyMap* keys_to_unlock) {
class Handler : public WriteBatch::Handler {
public:
// Sorted map of column_family_id to sorted set of keys.
// Since LockBatch() always locks keys in sorted order, it cannot deadlock
// with itself. We're not using a comparator here since it doesn't matter
// what the sorting is as long as it's consistent.
std::map<uint32_t, std::set<std::string>> keys_;
Handler() {}
void RecordKey(uint32_t column_family_id, const Slice& key) {
std::string key_str = key.ToString();
auto iter = (keys_)[column_family_id].find(key_str);
if (iter == (keys_)[column_family_id].end()) {
// key not yet seen, store it.
(keys_)[column_family_id].insert({std::move(key_str)});
}
}
virtual Status PutCF(uint32_t column_family_id, const Slice& key,
const Slice& /* unused */) override {
RecordKey(column_family_id, key);
return Status::OK();
}
virtual Status MergeCF(uint32_t column_family_id, const Slice& key,
const Slice& /* unused */) override {
RecordKey(column_family_id, key);
return Status::OK();
}
virtual Status DeleteCF(uint32_t column_family_id,
const Slice& key) override {
RecordKey(column_family_id, key);
return Status::OK();
}
};
// Iterating on this handler will add all keys in this batch into keys
Handler handler;
batch->Iterate(&handler);
Status s;
// Attempt to lock all keys
for (const auto& cf_iter : handler.keys_) {
uint32_t cfh_id = cf_iter.first;
auto& cfh_keys = cf_iter.second;
for (const auto& key_iter : cfh_keys) {
const std::string& key = key_iter;
s = txn_db_impl_->TryLock(this, cfh_id, key, true /* exclusive */);
if (!s.ok()) {
break;
}
TrackKey(keys_to_unlock, cfh_id, std::move(key), kMaxSequenceNumber,
false, true /* exclusive */);
}
if (!s.ok()) {
break;
}
}
if (!s.ok()) {
txn_db_impl_->UnLock(this, keys_to_unlock);
}
return s;
}
// Attempt to lock this key.
// Returns OK if the key has been successfully locked. Non-ok, otherwise.
// If check_shapshot is true and this transaction has a snapshot set,
// this key will only be locked if there have been no writes to this key since
// the snapshot time.
Status PessimisticTransaction::TryLock(ColumnFamilyHandle* column_family,
const Slice& key, bool read_only,
bool exclusive, bool untracked) {
uint32_t cfh_id = GetColumnFamilyID(column_family);
std::string key_str = key.ToString();
bool previously_locked;
bool lock_upgrade = false;
Status s;
// lock this key if this transactions hasn't already locked it
SequenceNumber current_seqno = kMaxSequenceNumber;
SequenceNumber new_seqno = kMaxSequenceNumber;
const auto& tracked_keys = GetTrackedKeys();
const auto tracked_keys_cf = tracked_keys.find(cfh_id);
if (tracked_keys_cf == tracked_keys.end()) {
previously_locked = false;
} else {
auto iter = tracked_keys_cf->second.find(key_str);
if (iter == tracked_keys_cf->second.end()) {
previously_locked = false;
} else {
if (!iter->second.exclusive && exclusive) {
lock_upgrade = true;
}
previously_locked = true;
current_seqno = iter->second.seq;
}
}
// Lock this key if this transactions hasn't already locked it or we require
// an upgrade.
if (!previously_locked || lock_upgrade) {
s = txn_db_impl_->TryLock(this, cfh_id, key_str, exclusive);
}
SetSnapshotIfNeeded();
// Even though we do not care about doing conflict checking for this write,
// we still need to take a lock to make sure we do not cause a conflict with
// some other write. However, we do not need to check if there have been
// any writes since this transaction's snapshot.
// TODO(agiardullo): could optimize by supporting shared txn locks in the
// future
if (untracked || snapshot_ == nullptr) {
// Need to remember the earliest sequence number that we know that this
// key has not been modified after. This is useful if this same
// transaction
// later tries to lock this key again.
if (current_seqno == kMaxSequenceNumber) {
// Since we haven't checked a snapshot, we only know this key has not
// been modified since after we locked it.
new_seqno = db_->GetLatestSequenceNumber();
} else {
new_seqno = current_seqno;
}
} else {
// If a snapshot is set, we need to make sure the key hasn't been modified
// since the snapshot. This must be done after we locked the key.
if (s.ok()) {
s = ValidateSnapshot(column_family, key, current_seqno, &new_seqno);
if (!s.ok()) {
// Failed to validate key
if (!previously_locked) {
// Unlock key we just locked
if (lock_upgrade) {
s = txn_db_impl_->TryLock(this, cfh_id, key_str,
false /* exclusive */);
assert(s.ok());
} else {
txn_db_impl_->UnLock(this, cfh_id, key.ToString());
}
}
}
}
}
if (s.ok()) {
// Let base class know we've conflict checked this key.
TrackKey(cfh_id, key_str, new_seqno, read_only, exclusive);
}
return s;
}
// Return OK() if this key has not been modified more recently than the
// transaction snapshot_.
Status PessimisticTransaction::ValidateSnapshot(
ColumnFamilyHandle* column_family, const Slice& key,
SequenceNumber prev_seqno, SequenceNumber* new_seqno) {
assert(snapshot_);
SequenceNumber seq = snapshot_->GetSequenceNumber();
if (prev_seqno <= seq) {
// If the key has been previous validated at a sequence number earlier
// than the curent snapshot's sequence number, we already know it has not
// been modified.
return Status::OK();
}
*new_seqno = seq;
ColumnFamilyHandle* cfh =
column_family ? column_family : db_impl_->DefaultColumnFamily();
return TransactionUtil::CheckKeyForConflicts(db_impl_, cfh, key.ToString(),
snapshot_->GetSequenceNumber(),
false /* cache_only */);
}
bool PessimisticTransaction::TryStealingLocks() {
assert(IsExpired());
TransactionState expected = STARTED;
return std::atomic_compare_exchange_strong(&txn_state_, &expected,
LOCKS_STOLEN);
}
void PessimisticTransaction::UnlockGetForUpdate(
ColumnFamilyHandle* column_family, const Slice& key) {
txn_db_impl_->UnLock(this, GetColumnFamilyID(column_family), key.ToString());
}
Status PessimisticTransaction::SetName(const TransactionName& name) {
Status s;
if (txn_state_ == STARTED) {
if (name_.length()) {
s = Status::InvalidArgument("Transaction has already been named.");
} else if (txn_db_impl_->GetTransactionByName(name) != nullptr) {
s = Status::InvalidArgument("Transaction name must be unique.");
} else if (name.length() < 1 || name.length() > 512) {
s = Status::InvalidArgument(
"Transaction name length must be between 1 and 512 chars.");
} else {
name_ = name;
txn_db_impl_->RegisterTransaction(this);
}
} else {
s = Status::InvalidArgument("Transaction is beyond state for naming.");
}
return s;
}
} // namespace rocksdb
#endif // ROCKSDB_LITE