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dragonflydb-dragonfly/server/transaction.cc
Roman Gershman e1c852dfcc Initial support for lua transactions.
Extend multi-transactions to scripts. Differentiate between incremental and instant locking
for multi-transactions.
2022-02-24 14:11:51 +02:00

1157 lines
37 KiB
C++

// Copyright 2021, Roman Gershman. All rights reserved.
// See LICENSE for licensing terms.
//
#include "server/transaction.h"
#include <absl/strings/match.h>
#include "base/logging.h"
#include "server/command_registry.h"
#include "server/db_slice.h"
#include "server/engine_shard_set.h"
namespace dfly {
using namespace std;
using namespace util;
thread_local Transaction::TLTmpSpace Transaction::tmp_space;
namespace {
std::atomic_uint64_t op_seq{1};
[[maybe_unused]] constexpr size_t kTransSize = sizeof(Transaction);
} // namespace
struct Transaction::FindFirstProcessor {
public:
FindFirstProcessor(TxId notify, unsigned size)
: find_res_(size, OpStatus::KEY_NOTFOUND), notify_txid_(notify) {
}
void Find(Transaction* t);
OpResult<Transaction::FindFirstResult> Process(Transaction* t);
private:
OpStatus RunInShard(Transaction* t, EngineShard* shard);
// Holds Find results: (iterator to a found key, and its index in the passed arguments).
// See DbSlice::FindFirst for more details.
// spans all the shards for now.
std::vector<OpResult<std::pair<MainIterator, unsigned>>> find_res_;
TxId notify_txid_;
};
void Transaction::FindFirstProcessor::Find(Transaction* t) {
VLOG(2) << "FindFirst::Find " << t->DebugId();
t->Execute([this](auto* t, auto* s) { return RunInShard(t, s); }, false);
}
OpStatus Transaction::FindFirstProcessor::RunInShard(Transaction* t, EngineShard* shard) {
if (notify_txid_ == kuint64max || shard->committed_txid() == notify_txid_) {
// TODO: to add timestamp logic that provides consistency guarantees for blocking transactions.
auto args = t->ShardArgsInShard(shard->shard_id());
find_res_[shard->shard_id()] = shard->db_slice().FindFirst(t->db_index(), args);
}
return OpStatus::OK;
}
OpResult<Transaction::FindFirstResult> Transaction::FindFirstProcessor::Process(Transaction* t) {
uint32_t min_arg_indx = UINT32_MAX;
FindFirstResult result;
for (size_t sid = 0; sid < find_res_.size(); ++sid) {
const auto& fr = find_res_[sid];
auto status = fr.status();
if (status == OpStatus::KEY_NOTFOUND)
continue;
if (status == OpStatus::WRONG_TYPE) {
return status;
}
DCHECK(fr && IsValid(fr->first));
const auto& it_pos = fr.value();
size_t arg_indx = t->ReverseArgIndex(sid, it_pos.second);
if (arg_indx < min_arg_indx) {
min_arg_indx = arg_indx;
result.sid = sid;
result.find_res = it_pos.first;
}
}
if (result.sid == kInvalidSid) {
return OpStatus::KEY_NOTFOUND;
}
return result;
}
IntentLock::Mode Transaction::Mode() const {
return (cid_->opt_mask() & CO::READONLY) ? IntentLock::SHARED : IntentLock::EXCLUSIVE;
}
/**
* @brief Construct a new Transaction:: Transaction object
*
* @param cid
* @param ess
* @param cs
*/
Transaction::Transaction(const CommandId* cid, EngineShardSet* ess) : cid_(cid), ess_(ess) {
string_view cmd_name(cid_->name());
if (cmd_name == "EXEC" || cmd_name == "EVAL" || cmd_name == "EVALSHA") {
multi_.reset(new Multi);
multi_->multi_opts = cid->opt_mask();
if (cmd_name == "EVAL" || cmd_name == "EVALSHA") {
multi_->incremental = false; // we lock all the keys at once.
}
}
}
Transaction::~Transaction() {
DVLOG(2) << "Transaction " << DebugId() << " destroyed";
}
/**
*
* There are 4 options that we consider here:
* a. T spans a single shard and its not multi.
* unique_shard_id_ is predefined before the schedule() is called.
* In that case only a single thread will be scheduled and it will use shard_data[0] just becase
* shard_data.size() = 1. Coordinator thread can access any data because there is a
* schedule barrier between InitByArgs and RunInShard/IsArmedInShard functions.
* b. T spans multiple shards and its not multi
* In that case multiple threads will be scheduled. Similarly they have a schedule barrier,
* and IsArmedInShard can read any variable from shard_data[x].
* c. Trans spans a single shard and it's multi. shard_data has size of ess_.size.
* IsArmedInShard will check shard_data[x].
* d. Trans spans multiple shards and it's multi. Similarly shard_data[x] will be checked.
* unique_shard_cnt_ and unique_shard_id_ are not accessed until shard_data[x] is armed, hence
* we have a barrier between coordinator and engine-threads. Therefore there should not be
* data races.
*
**/
void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
db_index_ = index;
if (IsGlobal()) {
unique_shard_cnt_ = ess_->size();
shard_data_.resize(unique_shard_cnt_);
return;
}
CHECK_GT(args.size(), 1U); // first entry is the command name.
DCHECK_EQ(unique_shard_cnt_, 0u);
KeyIndex key_index = DetermineKeys(cid_, args);
if (key_index.start == args.size()) { // eval with 0 keys.
CHECK(absl::StartsWith(cid_->name(), "EVAL"));
return;
}
DCHECK_LT(key_index.start, args.size());
DCHECK_GT(key_index.start, 0u);
bool incremental_locking = multi_ && multi_->incremental;
bool single_key = !multi_ && (key_index.start + key_index.step) >= key_index.end;
if (single_key) {
shard_data_.resize(1); // Single key optimization
auto key = ArgS(args, key_index.start);
args_.push_back(key);
unique_shard_cnt_ = 1;
unique_shard_id_ = Shard(key, ess_->size());
return;
}
// Our shard_data is not sparse, so we must allocate for all threads :(
shard_data_.resize(ess_->size());
CHECK(key_index.step == 1 || key_index.step == 2);
DCHECK(key_index.step == 1 || (args.size() % 2) == 1);
// Reuse thread-local temporary storage. Since this code is atomic we can use it here.
auto& shard_index = tmp_space.shard_cache;
shard_index.resize(shard_data_.size());
for (auto& v : shard_index) {
v.Clear();
}
// TODO: to determine correctly locking mode for transactions, scripts
// and regular commands.
IntentLock::Mode mode = IntentLock::EXCLUSIVE;
bool should_record_locks = false;
if (multi_) {
mode = Mode();
tmp_space.uniq_keys.clear();
DCHECK_LT(int(mode), 2);
should_record_locks = incremental_locking || !multi_->locks_recorded;
}
for (unsigned i = key_index.start; i < key_index.end; ++i) {
string_view key = ArgS(args, i);
uint32_t sid = Shard(key, shard_data_.size());
shard_index[sid].args.push_back(key);
shard_index[sid].original_index.push_back(i - 1);
if (should_record_locks && tmp_space.uniq_keys.insert(key).second) {
multi_->locks[key].cnt[int(mode)]++;
};
if (key_index.step == 2) { // value
++i;
auto val = ArgS(args, i);
shard_index[sid].args.push_back(val);
shard_index[sid].original_index.push_back(i - 1);
}
}
if (multi_) {
multi_->locks_recorded = true;
}
args_.resize(key_index.end - key_index.start);
reverse_index_.resize(args_.size());
auto next_arg = args_.begin();
auto rev_indx_it = reverse_index_.begin();
// slice.arg_start/arg_count point to args_ array which is sorted according to shard of each key.
// reverse_index_[i] says what's the original position of args_[i] in args.
for (size_t i = 0; i < shard_data_.size(); ++i) {
auto& sd = shard_data_[i];
auto& si = shard_index[i];
CHECK_LT(si.args.size(), 1u << 15);
sd.arg_count = si.args.size();
sd.arg_start = next_arg - args_.begin();
// We reset the local_mask for incremental locking to allow locking of arguments
// for each operation within the same transaction. For instant locking we lock at
// the beginning all the keys so we must preserve the mask to avoid double locking.
if (incremental_locking) {
sd.local_mask = 0;
}
if (!sd.arg_count)
continue;
++unique_shard_cnt_;
unique_shard_id_ = i;
uint32_t orig_indx = 0;
for (size_t j = 0; j < si.args.size(); ++j) {
*next_arg = si.args[j];
*rev_indx_it = si.original_index[orig_indx];
++next_arg;
++orig_indx;
++rev_indx_it;
}
}
CHECK(next_arg == args_.end());
DVLOG(1) << "InitByArgs " << DebugId() << " " << args_.front();
if (unique_shard_cnt_ == 1) {
PerShardData* sd;
if (multi_) {
sd = &shard_data_[unique_shard_id_];
} else {
shard_data_.resize(1);
sd = &shard_data_.front();
}
sd->arg_count = -1;
sd->arg_start = -1;
}
// Validation.
for (const auto& sd : shard_data_) {
// sd.local_mask may be non-zero for multi transactions with instant locking.
// Specifically EVALs may maintain state between calls.
DCHECK_EQ(0, sd.local_mask & ARMED);
if (!multi_) {
DCHECK_EQ(TxQueue::kEnd, sd.pq_pos);
}
}
}
void Transaction::SetExecCmd(const CommandId* cid) {
DCHECK(multi_);
DCHECK(!cb_);
// The order is important, we are Schedule() for multi transaction before overriding cid_.
// TODO: The flow is ugly. I should introduce a proper interface for Multi transactions
// like SetupMulti/TurndownMulti. We already have UnlockMulti that should be part of
// TurndownMulti.
if (txid_ == 0) {
Schedule();
}
unique_shard_cnt_ = 0;
cid_ = cid;
cb_ = nullptr;
}
string Transaction::DebugId() const {
return absl::StrCat(Name(), "@", txid_, "/", unique_shard_cnt_, " (", trans_id(this), ")");
}
// Runs in the dbslice thread. Returns true if transaction needs to be kept in the queue.
bool Transaction::RunInShard(EngineShard* shard) {
DCHECK_GT(run_count_.load(memory_order_relaxed), 0u);
CHECK(cb_) << DebugId();
DCHECK_GT(txid_, 0u);
// Unlike with regular transactions we do not acquire locks upon scheduling
// because Scheduling is done before multi-exec batch is executed. Therefore we
// lock keys right before the execution of each statement.
DVLOG(1) << "RunInShard: " << DebugId() << " sid:" << shard->shard_id();
unsigned idx = SidToId(shard->shard_id());
auto& sd = shard_data_[idx];
DCHECK(sd.local_mask & ARMED);
sd.local_mask &= ~ARMED;
DCHECK_EQ(sd.local_mask & (SUSPENDED_Q | EXPIRED_Q), 0);
bool awaked_prerun = (sd.local_mask & AWAKED_Q) != 0;
bool incremental_lock = multi_ && multi_->incremental;
// For multi we unlock transaction (i.e. its keys) in UnlockMulti() call.
// Therefore we differentiate between concluding, which says that this specific
// runnable concludes current operation, and should_release which tells
// whether we should unlock the keys. should_release is false for multi and
// equal to concluding otherwise.
bool should_release = (coordinator_state_ & COORD_EXEC_CONCLUDING) && !multi_;
IntentLock::Mode mode = Mode();
// We make sure that we lock exactly once for each (multi-hop) transaction inside
// transactions that lock incrementally.
if (incremental_lock && ((sd.local_mask & KEYLOCK_ACQUIRED) == 0)) {
DCHECK(!awaked_prerun); // we should not have blocking transaction inside multi block.
sd.local_mask |= KEYLOCK_ACQUIRED;
shard->db_slice().Acquire(mode, GetLockArgs(idx));
}
DCHECK(IsGlobal() || (sd.local_mask & KEYLOCK_ACQUIRED));
/*************************************************************************/
// Actually running the callback.
OpStatus status = cb_(this, shard);
/*************************************************************************/
if (unique_shard_cnt_ == 1) {
cb_ = nullptr; // We can do it because only a single thread runs the callback.
local_result_ = status;
} else {
CHECK_EQ(OpStatus::OK, status);
}
// at least the coordinator thread owns the reference.
DCHECK_GE(use_count(), 1u);
// we remove tx from tx-queue upon first invocation.
// if it needs to run again it runs via a dedicated continuation_trans_ state in EngineShard.
if (sd.pq_pos != TxQueue::kEnd) {
shard->txq()->Remove(sd.pq_pos);
sd.pq_pos = TxQueue::kEnd;
}
// If it's a final hop we should release the locks.
if (should_release) {
bool is_suspended = sd.local_mask & SUSPENDED_Q;
if (IsGlobal()) {
DCHECK(!awaked_prerun && !is_suspended); // Global transactions can not be blocking.
shard->shard_lock()->Release(Mode());
} else { // not global.
KeyLockArgs largs = GetLockArgs(idx);
// If a transaction has been suspended, we keep the lock so that future transaction
// touching those keys will be ordered via TxQueue. It's necessary because we preserve
// the atomicity of awaked transactions by halting the TxQueue.
if (!is_suspended) {
shard->db_slice().Release(mode, largs);
sd.local_mask &= ~KEYLOCK_ACQUIRED;
}
sd.local_mask &= ~OUT_OF_ORDER;
// It has 2 responsibilities.
// 1: to go over potential wakened keys, verify them and activate watch queues.
// 2: if this transaction was notified and finished running - to remove it from the head
// of the queue and notify the next one.
shard->ProcessAwakened(awaked_prerun ? this : nullptr);
}
}
CHECK_GE(DecreaseRunCnt(), 1u);
// From this point on we can not access 'this'.
return !should_release; // keep
}
void Transaction::RunNoop(EngineShard* shard) {
DVLOG(1) << "RunNoop " << DebugId();
unsigned idx = SidToId(shard->shard_id());
auto& sd = shard_data_[idx];
DCHECK(sd.local_mask & ARMED);
DCHECK(sd.local_mask & KEYLOCK_ACQUIRED);
DCHECK(!multi_);
DCHECK(!IsGlobal());
sd.local_mask &= ~ARMED;
if (unique_shard_cnt_ == 1) {
cb_ = nullptr;
local_result_ = OpStatus::OK;
}
if (coordinator_state_ & COORD_EXEC_CONCLUDING) {
KeyLockArgs largs = GetLockArgs(idx);
shard->db_slice().Release(Mode(), largs);
sd.local_mask &= ~KEYLOCK_ACQUIRED;
if (sd.local_mask & SUSPENDED_Q) {
sd.local_mask |= EXPIRED_Q;
shard->GCWatched(largs);
}
}
// Decrease run count after we update all the data in the transaction object.
CHECK_GE(DecreaseRunCnt(), 1u);
}
void Transaction::ScheduleInternal() {
DCHECK_EQ(0u, txid_);
DCHECK_EQ(0, coordinator_state_ & (COORD_SCHED | COORD_OOO));
bool span_all = IsGlobal();
bool single_hop = (coordinator_state_ & COORD_EXEC_CONCLUDING);
uint32_t num_shards;
std::function<bool(uint32_t)> is_active;
// TODO: For multi-transactions we should be able to deduce mode() at run-time based
// on the context. For regular multi-transactions we can actually inspect all commands.
// For eval-like transactions - we can decided based on the command flavor (EVAL/EVALRO) or
// auto-tune based on the static analysis (by identifying commands with hardcoded command names).
IntentLock::Mode mode = Mode();
if (span_all) {
is_active = [](uint32_t) { return true; };
num_shards = ess_->size();
// Lock shards
auto cb = [mode](EngineShard* shard) { shard->shard_lock()->Acquire(mode); };
ess_->RunBriefInParallel(std::move(cb));
} else {
num_shards = unique_shard_cnt_;
DCHECK_GT(num_shards, 0u);
is_active = [&](uint32_t i) {
return num_shards == 1 ? (i == unique_shard_id_) : shard_data_[i].arg_count > 0;
};
}
while (true) {
txid_ = op_seq.fetch_add(1, std::memory_order_relaxed);
std::atomic_uint32_t lock_granted_cnt{0};
std::atomic_uint32_t success{0};
auto cb = [&](EngineShard* shard) {
pair<bool, bool> res = ScheduleInShard(shard);
success.fetch_add(res.first, memory_order_relaxed);
lock_granted_cnt.fetch_add(res.second, memory_order_relaxed);
};
ess_->RunBriefInParallel(std::move(cb), is_active);
if (success.load(memory_order_acquire) == num_shards) {
// We allow out of order execution only for single hop transactions.
// It might be possible to do it for multi-hop transactions as well but currently is
// too complicated to reason about.
if (single_hop && lock_granted_cnt.load(memory_order_relaxed) == num_shards) {
// OOO can not happen with span-all transactions. We ensure it in ScheduleInShard when we
// refuse to acquire locks for these transactions..
DCHECK(!span_all);
coordinator_state_ |= COORD_OOO;
}
DVLOG(1) << "Scheduled " << DebugId()
<< " OutOfOrder: " << bool(coordinator_state_ & COORD_OOO);
coordinator_state_ |= COORD_SCHED;
break;
}
DVLOG(1) << "Cancelling " << DebugId();
auto cancel = [&](EngineShard* shard) {
success.fetch_sub(CancelInShard(shard), memory_order_relaxed);
};
ess_->RunBriefInParallel(std::move(cancel), is_active);
CHECK_EQ(0u, success.load(memory_order_relaxed));
}
if (IsOOO()) {
for (auto& sd : shard_data_) {
sd.local_mask |= OUT_OF_ORDER;
}
}
}
// Optimized "Schedule and execute" function for the most common use-case of a single hop
// transactions like set/mset/mget etc. Does not apply for more complicated cases like RENAME or
// BLPOP where a data must be read from multiple shards before performing another hop.
OpStatus Transaction::ScheduleSingleHop(RunnableType cb) {
DCHECK(!cb_);
cb_ = std::move(cb);
// single hop -> concluding.
coordinator_state_ |= (COORD_EXEC | COORD_EXEC_CONCLUDING);
if (!multi_) { // for non-multi transactions we schedule exactly once.
DCHECK_EQ(0, coordinator_state_ & COORD_SCHED);
}
bool schedule_fast = (unique_shard_cnt_ == 1) && !IsGlobal() && !multi_;
if (schedule_fast) { // Single shard (local) optimization.
// We never resize shard_data because that would affect MULTI transaction correctness.
DCHECK_EQ(1u, shard_data_.size());
shard_data_[0].local_mask |= ARMED;
// memory_order_release because we do not want it to be reordered with shard_data writes
// above.
// IsArmedInShard() first checks run_count_ before accessing shard_data.
run_count_.fetch_add(1, memory_order_release);
// Please note that schedule_cb can not update any data on ScheduleSingleHop stack
// since the latter can exit before ScheduleUniqueShard returns.
// The problematic flow is as follows: ScheduleUniqueShard schedules into TxQueue and then
// call PollExecute that runs the callback which calls DecreaseRunCnt.
// As a result WaitForShardCallbacks below is unblocked.
auto schedule_cb = [&] {
bool run_eager = ScheduleUniqueShard(EngineShard::tlocal());
if (run_eager) {
// it's important to DecreaseRunCnt only for run_eager and after run_eager was assigned.
// If DecreaseRunCnt were called before ScheduleUniqueShard finishes
// then WaitForShardCallbacks below could exit before schedule_cb assigns return value
// to run_eager and cause stack corruption.
CHECK_GE(DecreaseRunCnt(), 1u);
}
};
ess_->Add(unique_shard_id_, std::move(schedule_cb)); // serves as a barrier.
} else {
// Transaction spans multiple shards or it's global (like flushdb) or multi.
if (!multi_)
ScheduleInternal();
ExecuteAsync();
}
DVLOG(1) << "ScheduleSingleHop before Wait " << DebugId() << " " << run_count_.load();
WaitForShardCallbacks();
DVLOG(1) << "ScheduleSingleHop after Wait " << DebugId();
cb_ = nullptr;
return local_result_;
}
// Runs in the coordinator fiber.
void Transaction::UnlockMulti() {
VLOG(1) << "UnlockMulti " << DebugId();
DCHECK(multi_);
using KeyList = vector<pair<std::string_view, LockCnt>>;
vector<KeyList> sharded_keys(ess_->size());
// It's LE and not EQ because there may be callbacks in progress that increase use_count_.
DCHECK_LE(1u, use_count());
for (const auto& k_v : multi_->locks) {
ShardId sid = Shard(k_v.first, sharded_keys.size());
sharded_keys[sid].push_back(k_v);
}
auto cb = [&] {
EngineShard* shard = EngineShard::tlocal();
if (multi_->multi_opts & CO::GLOBAL_TRANS) {
shard->shard_lock()->Release(IntentLock::EXCLUSIVE);
}
ShardId sid = shard->shard_id();
for (const auto& k_v : sharded_keys[sid]) {
auto release = [&](IntentLock::Mode mode) {
if (k_v.second.cnt[mode]) {
shard->db_slice().Release(mode, this->db_index_, k_v.first, k_v.second.cnt[mode]);
}
};
release(IntentLock::SHARED);
release(IntentLock::EXCLUSIVE);
}
auto& sd = shard_data_[SidToId(shard->shard_id())];
// It does not have to be that all shards in multi transaction execute this tx.
// Hence it could stay in the tx queue. We perform the necessary cleanup and remove it from
// there.
if (sd.pq_pos != TxQueue::kEnd) {
DVLOG(1) << "unlockmulti: TxPopFront " << DebugId();
TxQueue* txq = shard->txq();
DCHECK(!txq->Empty());
Transaction* trans = absl::get<Transaction*>(txq->Front());
DCHECK(trans == this);
txq->PopFront();
sd.pq_pos = TxQueue::kEnd;
}
shard->ShutdownMulti(this);
// notify awakened transactions.
shard->ProcessAwakened(nullptr);
shard->PollExecution("unlockmulti", nullptr);
this->DecreaseRunCnt();
};
uint32_t prev = run_count_.fetch_add(shard_data_.size(), memory_order_relaxed);
DCHECK_EQ(prev, 0u);
for (ShardId i = 0; i < shard_data_.size(); ++i) {
ess_->Add(i, cb);
}
WaitForShardCallbacks();
DCHECK_GE(use_count(), 1u);
VLOG(1) << "UnlockMultiEnd " << DebugId();
}
// Runs in coordinator thread.
void Transaction::Execute(RunnableType cb, bool conclude) {
cb_ = std::move(cb);
coordinator_state_ |= COORD_EXEC;
if (conclude) {
coordinator_state_ |= COORD_EXEC_CONCLUDING;
} else {
coordinator_state_ &= ~COORD_EXEC_CONCLUDING;
}
ExecuteAsync();
DVLOG(1) << "Wait on Exec " << DebugId();
WaitForShardCallbacks();
DVLOG(1) << "Wait on Exec " << DebugId() << " completed";
cb_ = nullptr;
}
// Runs in coordinator thread.
void Transaction::ExecuteAsync() {
DVLOG(1) << "ExecuteAsync " << DebugId();
DCHECK_GT(unique_shard_cnt_, 0u);
DCHECK_GT(use_count_.load(memory_order_relaxed), 0u);
// We do not necessarily Execute this transaction in 'cb' below. It well may be that it will be
// executed by the engine shard once it has been armed and coordinator thread will finish the
// transaction before engine shard thread stops accessing it. Therefore, we increase reference
// by number of callbacks accessesing 'this' to allow callbacks to execute shard->Execute(this);
// safely.
use_count_.fetch_add(unique_shard_cnt_, memory_order_relaxed);
bool is_global = IsGlobal();
if (unique_shard_cnt_ == 1) {
shard_data_[SidToId(unique_shard_id_)].local_mask |= ARMED;
} else {
for (ShardId i = 0; i < shard_data_.size(); ++i) {
auto& sd = shard_data_[i];
if (!is_global && sd.arg_count == 0)
continue;
DCHECK_LT(sd.arg_count, 1u << 15);
sd.local_mask |= ARMED;
}
}
uint32_t seq = seqlock_.load(memory_order_relaxed);
// this fence prevents that a read or write operation before a release fence will be reordered
// with a write operation after a release fence. Specifically no writes below will be reordered
// upwards. Important, because it protects non-threadsafe local_mask from being accessed by
// IsArmedInShard in other threads.
run_count_.store(unique_shard_cnt_, memory_order_release);
// We verify seq lock has the same generation number. See below for more info.
auto cb = [seq, this] {
EngineShard* shard = EngineShard::tlocal();
uint16_t local_mask = GetLocalMask(shard->shard_id());
// we use fetch_add with release trick to make sure that local_mask is loaded before
// we load seq_after. We could gain similar result with "atomic_thread_fence(acquire)"
uint32_t seq_after = seqlock_.fetch_add(0, memory_order_release);
bool should_poll = (seq_after == seq) && (local_mask & ARMED);
DVLOG(2) << "EngineShard::Exec " << DebugId() << " sid:" << shard->shard_id() << " "
<< run_count_.load(memory_order_relaxed) << ", should_poll: " << should_poll;
// We verify that this callback is still relevant.
// If we still have the same sequence number and local_mask is ARMED it means
// the coordinator thread has not crossed WaitForShardCallbacks barrier.
// Otherwise, this callback is redundant. We may still call PollExecution but
// we should not pass this to it since it can be in undefined state for this callback.
if (should_poll) {
// shard->PollExecution(this) does not necessarily execute this transaction.
// Therefore, everything that should be handled during the callback execution
// should go into RunInShard.
shard->PollExecution("exec_cb", this);
}
DVLOG(2) << "ptr_release " << DebugId() << " " << seq;
intrusive_ptr_release(this); // against use_count_.fetch_add above.
};
// IsArmedInShard is the protector of non-thread safe data.
if (!is_global && unique_shard_cnt_ == 1) {
ess_->Add(unique_shard_id_, std::move(cb)); // serves as a barrier.
} else {
for (ShardId i = 0; i < shard_data_.size(); ++i) {
auto& sd = shard_data_[i];
if (!is_global && sd.arg_count == 0)
continue;
ess_->Add(i, cb); // serves as a barrier.
}
}
}
void Transaction::RunQuickie(EngineShard* shard) {
DCHECK(!multi_);
DCHECK_EQ(1u, shard_data_.size());
DCHECK_EQ(0u, txid_);
shard->IncQuickRun();
auto& sd = shard_data_[0];
DCHECK_EQ(0, sd.local_mask & (KEYLOCK_ACQUIRED | OUT_OF_ORDER));
DVLOG(1) << "RunQuickSingle " << DebugId() << " " << shard->shard_id() << " " << args_[0];
CHECK(cb_) << DebugId() << " " << shard->shard_id() << " " << args_[0];
local_result_ = cb_(this, shard);
sd.local_mask &= ~ARMED;
cb_ = nullptr; // We can do it because only a single shard runs the callback.
}
// runs in coordinator thread.
// Marks the transaction as expired but does not remove it from the waiting queue.
void Transaction::ExpireBlocking() {
DVLOG(1) << "ExpireBlocking " << DebugId();
DCHECK(!IsGlobal());
run_count_.store(unique_shard_cnt_, memory_order_release);
auto expire_cb = [this] {
EngineShard* shard = EngineShard::tlocal();
auto lock_args = GetLockArgs(shard->shard_id());
shard->db_slice().Release(Mode(), lock_args);
unsigned sd_idx = SidToId(shard->shard_id());
auto& sd = shard_data_[sd_idx];
sd.local_mask |= EXPIRED_Q;
sd.local_mask &= ~KEYLOCK_ACQUIRED;
// Need to see why I decided to call this.
// My guess - probably to trigger the run of stalled transactions in case
// this shard concurrently awoke this transaction and stalled the processing
// of TxQueue.
shard->PollExecution("expirecb", nullptr);
CHECK_GE(DecreaseRunCnt(), 1u);
};
if (unique_shard_cnt_ == 1) {
DCHECK_LT(unique_shard_id_, ess_->size());
ess_->Add(unique_shard_id_, std::move(expire_cb));
} else {
for (ShardId i = 0; i < shard_data_.size(); ++i) {
auto& sd = shard_data_[i];
DCHECK_EQ(0, sd.local_mask & ARMED);
if (sd.arg_count == 0)
continue;
ess_->Add(i, expire_cb);
}
}
// Wait for all callbacks to conclude.
WaitForShardCallbacks();
DVLOG(1) << "ExpireBlocking finished " << DebugId();
}
const char* Transaction::Name() const {
return cid_->name();
}
KeyLockArgs Transaction::GetLockArgs(ShardId sid) const {
KeyLockArgs res;
res.db_index = db_index_;
res.key_step = cid_->key_arg_step();
res.args = ShardArgsInShard(sid);
return res;
}
// Runs within a engine shard thread.
// Optimized path that schedules and runs transactions out of order if possible.
// Returns true if was eagerly executed, false if it was scheduled into queue.
bool Transaction::ScheduleUniqueShard(EngineShard* shard) {
DCHECK(!multi_);
DCHECK_EQ(0u, txid_);
DCHECK_EQ(1u, shard_data_.size());
auto mode = Mode();
auto lock_args = GetLockArgs(shard->shard_id());
auto& sd = shard_data_.front();
DCHECK_EQ(TxQueue::kEnd, sd.pq_pos);
// Fast path - for uncontended keys, just run the callback.
// That applies for single key operations like set, get, lpush etc.
if (shard->db_slice().CheckLock(mode, lock_args)) {
RunQuickie(shard);
return true;
}
// we can do it because only a single thread writes into txid_ and sd.
txid_ = op_seq.fetch_add(1, std::memory_order_relaxed);
sd.pq_pos = shard->txq()->Insert(this);
DCHECK_EQ(0, sd.local_mask & KEYLOCK_ACQUIRED);
bool lock_acquired = shard->db_slice().Acquire(mode, lock_args);
sd.local_mask |= KEYLOCK_ACQUIRED;
DCHECK(!lock_acquired); // Because CheckLock above failed.
DVLOG(1) << "Rescheduling into TxQueue " << DebugId();
shard->PollExecution("schedule_unique", nullptr);
return false;
}
// This function should not block since it's run via RunBriefInParallel.
pair<bool, bool> Transaction::ScheduleInShard(EngineShard* shard) {
// schedule_success, lock_granted.
pair<bool, bool> result{false, false};
if (shard->committed_txid() >= txid_) {
return result;
}
TxQueue* txq = shard->txq();
KeyLockArgs lock_args;
IntentLock::Mode mode = Mode();
bool spans_all = IsGlobal();
bool lock_granted = false;
ShardId sid = SidToId(shard->shard_id());
auto& sd = shard_data_[sid];
if (!spans_all) {
bool shard_unlocked = shard->shard_lock()->Check(mode);
lock_args = GetLockArgs(shard->shard_id());
// we need to acquire the lock unrelated to shard_unlocked since we register into Tx queue.
// All transactions in the queue must acquire the intent lock.
lock_granted = shard->db_slice().Acquire(mode, lock_args) && shard_unlocked;
sd.local_mask |= KEYLOCK_ACQUIRED;
DVLOG(1) << "Lock granted " << lock_granted << " for trans " << DebugId();
}
if (!txq->Empty()) {
// If the new transaction requires reordering of the pending queue (i.e. it comes before tail)
// and some other transaction already locked its keys we can not reorder 'trans' because
// that other transaction could have deduced that it can run OOO and eagerly execute. Hence, we
// fail this scheduling attempt for trans.
// However, when we schedule span-all transactions we can still reorder them. The reason is
// before we start scheduling them we lock the shards and disable OOO.
// We may record when they disable OOO via barrier_ts so if the queue contains transactions
// that were only scheduled afterwards we know they are not free so we can still
// reorder the queue. Currently, this optimization is disabled: barrier_ts < pq->HeadScore().
bool to_proceed = lock_granted || txq->TailScore() < txid_;
if (!to_proceed) {
if (sd.local_mask & KEYLOCK_ACQUIRED) { // rollback the lock.
shard->db_slice().Release(mode, lock_args);
sd.local_mask &= ~KEYLOCK_ACQUIRED;
}
return result; // false, false
}
}
result.second = lock_granted;
result.first = true;
TxQueue::Iterator it = txq->Insert(this);
DCHECK_EQ(TxQueue::kEnd, sd.pq_pos);
sd.pq_pos = it;
DVLOG(1) << "Insert into tx-queue, sid(" << sid << ") " << DebugId() << ", qlen " << txq->size();
return result;
}
bool Transaction::CancelInShard(EngineShard* shard) {
ShardId idx = SidToId(shard->shard_id());
auto& sd = shard_data_[idx];
auto pos = sd.pq_pos;
if (pos == TxQueue::kEnd)
return false;
sd.pq_pos = TxQueue::kEnd;
TxQueue* pq = shard->txq();
auto val = pq->At(pos);
Transaction* trans = absl::get<Transaction*>(val);
DCHECK(trans == this) << "Pos " << pos << ", pq size " << pq->size() << ", trans " << trans;
pq->Remove(pos);
if (sd.local_mask & KEYLOCK_ACQUIRED) {
auto mode = Mode();
auto lock_args = GetLockArgs(shard->shard_id());
shard->db_slice().Release(mode, lock_args);
sd.local_mask &= ~KEYLOCK_ACQUIRED;
}
return true;
}
// runs in engine-shard thread.
ArgSlice Transaction::ShardArgsInShard(ShardId sid) const {
DCHECK(!args_.empty());
DCHECK_NOTNULL(EngineShard::tlocal());
// We can read unique_shard_cnt_ only because ShardArgsInShard is called after IsArmedInShard
// barrier.
if (unique_shard_cnt_ == 1) {
return args_;
}
const auto& sd = shard_data_[sid];
return ArgSlice{args_.data() + sd.arg_start, sd.arg_count};
}
size_t Transaction::ReverseArgIndex(ShardId shard_id, size_t arg_index) const {
if (unique_shard_cnt_ == 1)
return arg_index;
return reverse_index_[shard_data_[shard_id].arg_start + arg_index];
}
bool Transaction::WaitOnWatch(const time_point& tp) {
// Assumes that transaction is pending and scheduled. TODO: To verify it with state machine.
VLOG(2) << "WaitOnWatch Start use_count(" << use_count() << ")";
using namespace chrono;
// wake_txid_.store(kuint64max, std::memory_order_relaxed);
Execute([](auto* t, auto* shard) { return t->AddToWatchedShardCb(shard); }, true);
coordinator_state_ |= COORD_BLOCKED;
bool res = true; // returns false if timeout occurs.
auto wake_cb = [this] {
return (coordinator_state_ & COORD_CANCELLED) ||
notify_txid_.load(memory_order_relaxed) != kuint64max;
};
cv_status status = cv_status::no_timeout;
if (tp == time_point::max()) {
DVLOG(1) << "WaitOnWatch foreva " << DebugId();
blocking_ec_.await(move(wake_cb));
DVLOG(1) << "WaitOnWatch AfterWait";
} else {
DVLOG(1) << "WaitOnWatch TimeWait for "
<< duration_cast<milliseconds>(tp - time_point::clock::now()).count() << " ms";
status = blocking_ec_.await_until(move(wake_cb), tp);
DVLOG(1) << "WaitOnWatch await_until " << int(status);
}
if ((coordinator_state_ & COORD_CANCELLED) || status == cv_status::timeout) {
ExpireBlocking();
coordinator_state_ &= ~COORD_BLOCKED;
return false;
}
// We were notified by a shard, so lets make sure that our notifications converged to a stable
// form.
if (unique_shard_cnt_ > 1) {
run_count_.store(unique_shard_cnt_, memory_order_release);
auto converge_cb = [this] {
EngineShard* shard = EngineShard::tlocal();
auto& sd = shard_data_[shard->shard_id()];
TxId notify = notify_txid();
if ((sd.local_mask & AWAKED_Q) || shard->HasResultConverged(notify)) {
CHECK_GE(DecreaseRunCnt(), 1u);
return;
}
shard->WaitForConvergence(notify, this);
};
for (ShardId i = 0; i < shard_data_.size(); ++i) {
auto& sd = shard_data_[i];
DCHECK_EQ(0, sd.local_mask & ARMED);
if (sd.arg_count == 0)
continue;
ess_->Add(i, converge_cb);
}
// Wait for all callbacks to conclude.
WaitForShardCallbacks();
DVLOG(1) << "Convergence finished " << DebugId();
}
// Lift blocking mask.
coordinator_state_ &= ~COORD_BLOCKED;
return res;
}
void Transaction::UnregisterWatch() {
auto cb = [](Transaction* t, EngineShard* shard) {
t->RemoveFromWatchedShardCb(shard);
return OpStatus::OK;
};
Execute(std::move(cb), true);
}
// Runs only in the shard thread.
OpStatus Transaction::AddToWatchedShardCb(EngineShard* shard) {
ShardId sid = SidToId(shard->shard_id());
auto& sd = shard_data_[sid];
CHECK_EQ(0, sd.local_mask & SUSPENDED_Q);
DCHECK_EQ(0, sd.local_mask & ARMED);
auto args = ShardArgsInShard(shard->shard_id());
for (auto s : args) {
shard->AddWatched(s, this);
}
sd.local_mask |= SUSPENDED_Q;
return OpStatus::OK;
}
// Runs only in the shard thread.
// Quadratic complexity in number of arguments and queue length.
bool Transaction::RemoveFromWatchedShardCb(EngineShard* shard) {
ShardId sid = SidToId(shard->shard_id());
auto& sd = shard_data_[sid];
constexpr uint16_t kQueueMask =
-Transaction::SUSPENDED_Q | Transaction::AWAKED_Q | Transaction::EXPIRED_Q;
if ((sd.local_mask & kQueueMask) == 0)
return false;
sd.local_mask &= kQueueMask;
// TODO: what if args have keys and values?
auto args = ShardArgsInShard(shard->shard_id());
for (auto s : args) {
shard->RemovedWatched(s, this);
}
return true;
}
inline uint32_t Transaction::DecreaseRunCnt() {
// to protect against cases where Transaction is destroyed before run_ec_.notify
// finishes running. We can not put it inside the (res == 1) block because then it's too late.
::boost::intrusive_ptr guard(this);
// We use release so that no stores will be reordered after.
uint32_t res = run_count_.fetch_sub(1, std::memory_order_release);
if (res == 1) {
run_ec_.notify();
}
return res;
}
bool Transaction::IsGlobal() const {
return (cid_->opt_mask() & CO::GLOBAL_TRANS) != 0;
}
// Runs only in the shard thread.
bool Transaction::NotifySuspended(TxId committed_txid, ShardId sid) {
unsigned sd_id = SidToId(sid);
auto& sd = shard_data_[sd_id];
unsigned local_mask = sd.local_mask;
CHECK_NE(0u, local_mask & SUSPENDED_Q);
DVLOG(1) << "NotifyBlocked " << DebugId() << ", local_mask: " << local_mask;
if (local_mask & Transaction::EXPIRED_Q) {
return false;
}
if (local_mask & SUSPENDED_Q) {
DCHECK_EQ(0u, local_mask & AWAKED_Q);
sd.local_mask &= ~SUSPENDED_Q;
sd.local_mask |= AWAKED_Q;
TxId notify_id = notify_txid_.load(memory_order_relaxed);
while (committed_txid < notify_id) {
if (notify_txid_.compare_exchange_weak(notify_id, committed_txid, memory_order_relaxed)) {
// if we improved notify_txid_ - break.
blocking_ec_.notify(); // release barrier.
break;
}
}
return true;
}
CHECK(sd.local_mask & AWAKED_Q);
return true;
}
void Transaction::BreakOnClose() {
if (coordinator_state_ & COORD_BLOCKED) {
coordinator_state_ |= COORD_CANCELLED;
blocking_ec_.notify();
}
}
auto Transaction::FindFirst() -> OpResult<FindFirstResult> {
FindFirstProcessor processor(notify_txid_.load(memory_order_relaxed), ess_->size());
processor.Find(this);
return processor.Process(this);
}
} // namespace dfly