From 1bb84cdbcf155ef05f348a5b130e83a373a71ebe Mon Sep 17 00:00:00 2001
From: Gleb Natapov <gleb@scylladb.com>
Date: Thu, 16 May 2019 16:27:47 +0300
Subject: [PATCH] cache_hitrate_calculator: do not copy stats map for each cpu

invoke_on_all() copies provided function for each shard it is executed
on, so by moving stats map into the capture we copy it for each shard
too. Avoid it by putting it into the top level object which is already
captured by reference.
Message-Id: <20190516132748.6469-2-gleb@scylladb.com>

(cherry picked from commit 4517c56a572236f0590624b6898d17aa7e6a895b)
---
 service/cache_hitrate_calculator.hh | 11 +++++++++++
 service/misc_services.cc            | 18 +++++-------------
 2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/service/cache_hitrate_calculator.hh b/service/cache_hitrate_calculator.hh
index 340f91ecb2..f6f13161d7 100644
--- a/service/cache_hitrate_calculator.hh
+++ b/service/cache_hitrate_calculator.hh
@@ -28,11 +28,22 @@
 namespace service {
 
 class cache_hitrate_calculator : public seastar::async_sharded_service<cache_hitrate_calculator> {
+    struct stat {
+        float h = 0;
+        float m = 0;
+        stat& operator+=(stat& o) {
+            h += o.h;
+            m += o.m;
+            return *this;
+        }
+    };
+
     seastar::sharded<database>& _db;
     seastar::sharded<cache_hitrate_calculator>& _me;
     timer<lowres_clock> _timer;
     bool _stopped = false;
     float _diff = 0;
+    std::unordered_map<utils::UUID, stat> _rates;
     future<> _done = make_ready_future();
 
     future<lowres_clock::duration> recalculate_hitrates();
diff --git a/service/misc_services.cc b/service/misc_services.cc
index f0483d6afe..d44426e4ad 100644
--- a/service/misc_services.cc
+++ b/service/misc_services.cc
@@ -112,16 +112,6 @@ void cache_hitrate_calculator::run_on(size_t master, lowres_clock::duration d) {
 }
 
 future<lowres_clock::duration> cache_hitrate_calculator::recalculate_hitrates() {
-    struct stat {
-        float h = 0;
-        float m = 0;
-        stat& operator+=(stat& o) {
-            h += o.h;
-            m += o.m;
-            return *this;
-        }
-    };
-
     auto non_system_filter = [&] (const std::pair<utils::UUID, lw_shared_ptr<column_family>>& cf) {
         return _db.local().find_keyspace(cf.second->schema()->ks_name()).get_replication_strategy().get_type() != locator::replication_strategy_type::local;
     };
@@ -143,12 +133,13 @@ future<lowres_clock::duration> cache_hitrate_calculator::recalculate_hitrates()
 
     return _db.map_reduce0(cf_to_cache_hit_stats, std::unordered_map<utils::UUID, stat>(), sum_stats_per_cf).then([this, non_system_filter] (std::unordered_map<utils::UUID, stat> rates) mutable {
         _diff = 0;
+        _rates = std::move(rates);
         // set calculated rates on all shards
-        return _db.invoke_on_all([this, rates = std::move(rates), cpuid = engine().cpu_id(), non_system_filter] (database& db) {
+        return _db.invoke_on_all([this, cpuid = engine().cpu_id(), non_system_filter] (database& db) {
             sstring gstate;
             for (auto& cf : db.get_column_families() | boost::adaptors::filtered(non_system_filter)) {
-                auto it = rates.find(cf.first);
-                if (it == rates.end()) { // a table may be added before map/reduce compltes and this code runs
+                auto it = _rates.find(cf.first);
+                if (it == _rates.end()) { // a table may be added before map/reduce completes and this code runs
                     continue;
                 }
                 stat s = it->second;
@@ -171,6 +162,7 @@ future<lowres_clock::duration> cache_hitrate_calculator::recalculate_hitrates()
             return make_ready_future<>();
         });
     }).then([this] {
+        _rates.clear();
         // if max difference during this round is big schedule next recalculate earlier
         if (_diff < 0.01) {
             return std::chrono::milliseconds(2000);