chore: introduce a secondary TaskQueue for shards (#3508)

Also allow the TaskQueue to support multiple consumer fibers.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

helio

@@ -1 +1 @@
-Subproject commit fb46b481e3eb82ecbc7bbf1d22b2fda7f5fac409
+Subproject commit f9e28c79d3f9234ab0f094a7101cad8b5847c184

src/core/task_queue.cc

@@ -4,8 +4,35 @@
 
 #include "core/task_queue.h"
 
+#include <absl/strings/str_cat.h>
+
+#include "base/logging.h"
+
+using namespace std;
 namespace dfly {
 
 __thread unsigned TaskQueue::blocked_submitters_ = 0;
 
+TaskQueue::TaskQueue(unsigned queue_size, unsigned start_size, unsigned pool_max_size)
+    : queue_(queue_size), consumer_fibers_(start_size), pool_max_size_(pool_max_size) {
+  CHECK_GT(start_size, 0u);
+  CHECK_LE(start_size, pool_max_size);
+}
+
+void TaskQueue::Start(std::string_view base_name) {
+  for (size_t i = 0; i < consumer_fibers_.size(); ++i) {
+    auto& fb = consumer_fibers_[i];
+    CHECK(!fb.IsJoinable());
+
+    string name = absl::StrCat(base_name, "/", i);
+    fb = util::fb2::Fiber(name, [this] { queue_.Run(); });
+  }
+}
+
+void TaskQueue::Shutdown() {
+  queue_.Shutdown();
+  for (auto& fb : consumer_fibers_)
+    fb.JoinIfNeeded();
+}
+
 }  // namespace dfly

src/core/task_queue.h

@@ -15,8 +15,8 @@ namespace dfly {
  */
 class TaskQueue {
  public:
-  explicit TaskQueue(unsigned queue_size = 128) : queue_(queue_size) {
-  }
+  // TODO: to add a mechanism to moderate pool size. Currently it's static with pool_start_size.
+  TaskQueue(unsigned queue_size, unsigned pool_start_size, unsigned pool_max_size);
 
   template <typename F> bool TryAdd(F&& f) {
     return queue_.TryAdd(std::forward<F>(f));
@@ -51,18 +51,13 @@ class TaskQueue {
    * @brief Start running consumer loop in the caller thread by spawning fibers.
    *        Returns immediately.
    */
-  void Start(std::string_view base_name) {
-    consumer_fiber_ = util::fb2::Fiber(base_name, [this] { queue_.Run(); });
-  }
+  void Start(std::string_view base_name);
 
   /**
    * @brief Notifies Run() function to empty the queue and to exit and waits for the consumer
    *        fiber to finish.
    */
-  void Shutdown() {
-    queue_.Shutdown();
-    consumer_fiber_.JoinIfNeeded();
-  }
+  void Shutdown();
 
   static unsigned blocked_submitters() {
     return blocked_submitters_;
@@ -70,7 +65,9 @@ class TaskQueue {
 
  private:
   util::fb2::FiberQueue queue_;
-  util::fb2::Fiber consumer_fiber_;
+  std::vector<util::fb2::Fiber> consumer_fibers_;
+  unsigned pool_max_size_;
+
   static __thread unsigned blocked_submitters_;
 };
 

src/server/engine_shard.cc

@@ -371,7 +371,8 @@ uint32_t EngineShard::DefragTask() {
 }
 
 EngineShard::EngineShard(util::ProactorBase* pb, mi_heap_t* heap)
-    : queue_(kQueueLen),
+    : queue_(kQueueLen, 1, 1),
+      queue2_(kQueueLen / 2, 2, 2),
       txq_([](const Transaction* t) { return t->txid(); }),
       mi_resource_(heap),
       shard_id_(pb->GetPoolIndex()) {
@@ -379,6 +380,7 @@ EngineShard::EngineShard(util::ProactorBase* pb, mi_heap_t* heap)
 
   defrag_task_ = pb->AddOnIdleTask([this]() { return DefragTask(); });
   queue_.Start(absl::StrCat("shard_queue_", shard_id()));
+  queue2_.Start(absl::StrCat("l2_queue_", shard_id()));
 }
 
 EngineShard::~EngineShard() {
@@ -389,7 +391,7 @@ void EngineShard::Shutdown() {
   DVLOG(1) << "EngineShard::Shutdown";
 
   queue_.Shutdown();
-
+  queue2_.Shutdown();
   DCHECK(!fiber_periodic_.IsJoinable());
 
   ProactorBase::me()->RemoveOnIdleTask(defrag_task_);

src/server/engine_shard.h

@@ -68,6 +68,10 @@ class EngineShard {
     return &queue_;
   }
 
+  TaskQueue* GetSecondaryQueue() {
+    return &queue2_;
+  }
+
   // Processes TxQueue, blocked transactions or any other execution state related to that
   // shard. Tries executing the passed transaction if possible (does not guarantee though).
   void PollExecution(const char* context, Transaction* trans);
@@ -223,7 +227,7 @@ class EngineShard {
   // return true if we did not complete the shard scan
   bool DoDefrag();
 
-  TaskQueue queue_;
+  TaskQueue queue_, queue2_;
 
   TxQueue txq_;
   MiMemoryResource mi_resource_;

src/server/engine_shard_set.cc

@@ -103,11 +103,11 @@ EngineShardSet* shard_set = nullptr;
 
 void EngineShardSet::Init(uint32_t sz, std::function<void()> shard_handler) {
   CHECK_EQ(0u, size());
-  shard_queue_.resize(sz);
-
+  shards_.reset(new EngineShard*[sz]);
+  size_ = sz;
   size_t max_shard_file_size = GetTieredFileLimit(sz);
-  pp_->AwaitFiberOnAll([&](uint32_t index, ProactorBase* pb) {
-    if (index < shard_queue_.size()) {
+  pp_->AwaitFiberOnAll([this](uint32_t index, ProactorBase* pb) {
+    if (index < size_) {
       InitThreadLocal(pb);
     }
   });
@@ -115,7 +115,7 @@ void EngineShardSet::Init(uint32_t sz, std::function<void()> shard_handler) {
   namespaces.Init();
 
   pp_->AwaitFiberOnAll([&](uint32_t index, ProactorBase* pb) {
-    if (index < shard_queue_.size()) {
+    if (index < size_) {
       auto* shard = EngineShard::tlocal();
       shard->InitTieredStorage(pb, max_shard_file_size);
 
@@ -144,7 +144,7 @@ void EngineShardSet::Shutdown() {
 void EngineShardSet::InitThreadLocal(ProactorBase* pb) {
   EngineShard::InitThreadLocal(pb);
   EngineShard* es = EngineShard::tlocal();
-  shard_queue_[es->shard_id()] = es->GetFiberQueue();
+  shards_[es->shard_id()] = es;
 }
 
 void EngineShardSet::TEST_EnableCacheMode() {

src/server/engine_shard_set.h

@@ -45,7 +45,7 @@ class EngineShardSet {
   }
 
   uint32_t size() const {
-    return uint32_t(shard_queue_.size());
+    return size_;
   }
 
   util::ProactorPool* pool() {
@@ -63,13 +63,17 @@ class EngineShardSet {
 
   // Uses a shard queue to dispatch. Callback runs in a dedicated fiber.
   template <typename F> auto Await(ShardId sid, F&& f) {
-    return shard_queue_[sid]->Await(std::forward<F>(f));
+    return shards_[sid]->GetFiberQueue()->Await(std::forward<F>(f));
   }
 
   // Uses a shard queue to dispatch. Callback runs in a dedicated fiber.
   template <typename F> auto Add(ShardId sid, F&& f) {
-    assert(sid < shard_queue_.size());
-    return shard_queue_[sid]->Add(std::forward<F>(f));
+    assert(sid < size_);
+    return shards_[sid]->GetFiberQueue()->Add(std::forward<F>(f));
+  }
+
+  template <typename F> auto AddL2(ShardId sid, F&& f) {
+    return shards_[sid]->GetSecondaryQueue()->Add(std::forward<F>(f));
   }
 
   // Runs a brief function on all shards. Waits for it to complete.
@@ -94,8 +98,8 @@ class EngineShardSet {
   // The functions running inside the shard queue run atomically (sequentially)
   // with respect each other on the same shard.
   template <typename U> void AwaitRunningOnShardQueue(U&& func) {
-    util::fb2::BlockingCounter bc(shard_queue_.size());
-    for (size_t i = 0; i < shard_queue_.size(); ++i) {
+    util::fb2::BlockingCounter bc(size_);
+    for (size_t i = 0; i < size_; ++i) {
       Add(i, [&func, bc]() mutable {
         func(EngineShard::tlocal());
         bc->Dec();
@@ -112,7 +116,8 @@ class EngineShardSet {
   void InitThreadLocal(util::ProactorBase* pb);
 
   util::ProactorPool* pp_;
-  std::vector<TaskQueue*> shard_queue_;
+  std::unique_ptr<EngineShard*[]> shards_;
+  uint32_t size_ = 0;
 };
 
 template <typename U, typename P>