chore: Remove manual memory management from stats (#2550)

Simplift stats memory management

Signed-off-by: Vladislav Oleshko <vlad@dragonflydb.io>

src/server/server_family.cc

@@ -1674,7 +1674,7 @@ Metrics ServerFamily::GetMetrics() const {
     result.fiber_longrun_cnt += fb2::FiberLongRunCnt();
     result.fiber_longrun_usec += fb2::FiberLongRunSumUsec();
 
-    result.coordinator_stats.Add(shard_set->size(), ss->stats);
+    result.coordinator_stats.Add(ss->stats);
 
     result.uptime = time(NULL) - this->start_time_;
     result.qps += uint64_t(ss->MovingSum6());

src/server/server_state.cc

@@ -23,32 +23,12 @@ namespace dfly {
 
 __thread ServerState* ServerState::state_ = nullptr;
 
-ServerState::Stats::Stats() {
+ServerState::Stats::Stats(unsigned num_shards) : tx_width_freq_arr(num_shards) {
   tx_type_cnt.fill(0);
 }
 
-ServerState::Stats::~Stats() {
-  delete[] tx_width_freq_arr;
-}
-
-auto ServerState::Stats::operator=(Stats&& other) -> Stats& {
-  for (int i = 0; i < NUM_TX_TYPES; ++i) {
-    this->tx_type_cnt[i] = other.tx_type_cnt[i];
-  }
-  this->eval_io_coordination_cnt = other.eval_io_coordination_cnt;
-  this->eval_shardlocal_coordination_cnt = other.eval_shardlocal_coordination_cnt;
-  this->eval_squashed_flushes = other.eval_squashed_flushes;
-  this->tx_schedule_cancel_cnt = other.tx_schedule_cancel_cnt;
-
-  delete[] this->tx_width_freq_arr;
-  this->tx_width_freq_arr = other.tx_width_freq_arr;
-  other.tx_width_freq_arr = nullptr;
-
-  return *this;
-}
-
-ServerState::Stats& ServerState::Stats::Add(unsigned num_shards, const ServerState::Stats& other) {
-  static_assert(sizeof(Stats) == 13 * 8, "Stats size mismatch");
+ServerState::Stats& ServerState::Stats::Add(const ServerState::Stats& other) {
+  static_assert(sizeof(Stats) == 14 * 8, "Stats size mismatch");
 
   for (int i = 0; i < NUM_TX_TYPES; ++i) {
     this->tx_type_cnt[i] += other.tx_type_cnt[i];
@@ -65,15 +45,12 @@ ServerState::Stats& ServerState::Stats::Add(unsigned num_shards, const ServerSta
 
   this->blocked_on_interpreter += other.blocked_on_interpreter;
 
-  if (this->tx_width_freq_arr == nullptr) {
-    this->tx_width_freq_arr = new uint64_t[num_shards];
-    std::copy_n(other.tx_width_freq_arr, num_shards, this->tx_width_freq_arr);
+  if (this->tx_width_freq_arr.size() > 0) {
+    DCHECK_EQ(this->tx_width_freq_arr.size(), other.tx_width_freq_arr.size());
+    this->tx_width_freq_arr += other.tx_width_freq_arr;
   } else {
-    for (unsigned i = 0; i < num_shards; ++i) {
-      this->tx_width_freq_arr[i] += other.tx_width_freq_arr[i];
-    }
+    this->tx_width_freq_arr = other.tx_width_freq_arr;
   }
-
   return *this;
 }
 
@@ -121,8 +98,7 @@ void ServerState::Init(uint32_t thread_index, uint32_t num_shards, acl::UserRegi
   state_->gstate_ = GlobalState::ACTIVE;
   state_->thread_index_ = thread_index;
   state_->user_registry = registry;
-  state_->stats.tx_width_freq_arr = new uint64_t[num_shards];
-  std::fill_n(state_->stats.tx_width_freq_arr, num_shards, 0);
+  state_->stats = Stats(num_shards);
 }
 
 void ServerState::Destroy() {

src/server/server_state.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <optional>
+#include <valarray>
 #include <vector>
 
 #include "base/histogram.h"
@@ -95,6 +96,15 @@ class ServerState {  // public struct - to allow initialization.
  public:
   enum TxType { GLOBAL, NORMAL, QUICK, INLINE, NUM_TX_TYPES };
   struct Stats {
+    Stats(unsigned num_shards = 0);  // Default initialization should be valid for Add()
+
+    Stats(Stats&& other) = default;
+    Stats& operator=(Stats&& other) = default;
+    Stats(const Stats&) = delete;
+    Stats& operator=(const Stats& other) = delete;
+
+    Stats& Add(const Stats& other);
+
     std::array<uint64_t, NUM_TX_TYPES> tx_type_cnt;
     uint64_t tx_schedule_cancel_cnt = 0;
 
@@ -108,23 +118,7 @@ class ServerState {  // public struct - to allow initialization.
 
     uint64_t blocked_on_interpreter = 0;
 
-    // Array of size of number of shards.
-    // Each entry is how many transactions we had with this width (unique_shard_cnt).
-    uint64_t* tx_width_freq_arr = nullptr;
-
-    Stats();
-    ~Stats();
-
-    Stats(Stats&& other) {
-      *this = std::move(other);
-    }
-
-    Stats& operator=(Stats&& other);
-
-    Stats& Add(unsigned num_shards, const Stats& other);
-
-    Stats(const Stats&) = delete;
-    Stats& operator=(const Stats&) = delete;
+    std::valarray<uint64_t> tx_width_freq_arr;
   };
 
   // Unsafe version.

src/server/test_utils.cc

@@ -318,11 +318,8 @@ unsigned BaseFamilyTest::NumLocked() {
 }
 
 void BaseFamilyTest::ClearMetrics() {
-  shard_set->pool()->Await([](auto*) {
-    ServerState::Stats stats;
-    stats.tx_width_freq_arr = new uint64_t[shard_set->size()];
-    ServerState::tlocal()->stats = std::move(stats);
-  });
+  shard_set->pool()->Await(
+      [](auto*) { ServerState::tlocal()->stats = ServerState::Stats(shard_set->size()); });
 }
 
 void BaseFamilyTest::WaitUntilLocked(DbIndex db_index, string_view key, double timeout) {