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bug(server): global command stalls on server load with pipeline mode (#1909)

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* bug(server): global command stalls on server load with pipeline mode
fixes #1797
the bug: global command is not able to schedule into txq when high load pipelined commands. Only after the load finish the global transaction gets scheduled into the txq. The reason for this is when we start a global transaction we set the shard lock and all the transactions start to enter the txq. They compete with the global tx on the order they are inserted into the queue to preserve transaction atomicity. Because the global tx needs to be inserted to all shard queues its chance to schedule with order with all the other transactions is low.
the solution: lock the global transaction inside the schedule in shard, locking closer to scheduling decreases the number of transactions in the queue and the competition on ordering correctly has higher chance now.

Signed-off-by: adi_holden <adi@dragonflydb.io>
This commit is contained in:
adiholden 2023-09-21 16:35:57 +03:00 • committed by GitHub
parent 08ed830d27
commit 36ac31427d
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GPG key ID: 4AEE18F83AFDEB23
4 changed files with 13 additions and 7 deletions
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16
src/server/transaction.cc
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@ -551,16 +551,9 @@ void Transaction::ScheduleInternal() {
// 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 = shard_set->size();
// Lock shards
auto cb = [mode](EngineShard* shard) { shard->shard_lock()->Acquire(mode); };
shard_set->RunBriefInParallel(std::move(cb));
VLOG(1) << "Global shard lock acquired";
} else {
num_shards = unique_shard_cnt_;
DCHECK_GT(num_shards, 0u);
@ -601,6 +594,7 @@ void Transaction::ScheduleInternal() {
}
VLOG(2) << "Cancelling " << DebugId();
ServerState::tlocal()->stats.tx_schedule_cancel_cnt += 1;
atomic_bool should_poll_execution{false};
auto cancel = [&](EngineShard* shard) {
@ -1047,6 +1041,11 @@ pair<bool, bool> Transaction::ScheduleInShard(EngineShard* shard) {
return {false, false};
}
if (IsGlobal()) {
shard->shard_lock()->Acquire(mode);
VLOG(1) << "Global shard lock acquired";
}
TxQueue::Iterator it = txq->Insert(this);
DCHECK_EQ(TxQueue::kEnd, sd.pq_pos);
sd.pq_pos = it;
@ -1080,6 +1079,9 @@ bool Transaction::CancelShardCb(EngineShard* shard) {
shard->db_slice().Release(mode, lock_args);
sd.local_mask &= ~KEYLOCK_ACQUIRED;
}
if (IsGlobal()) {
shard->shard_lock()->Release(Mode());
}
if (pos == head && !txq->Empty()) {
return true;