change IndexSet::addMetrics return type to pair<metrics, iterator> to reduce another find call

fdbserver/StorageMetrics.actor.cpp

@@ -549,9 +549,9 @@ void StorageServerMetrics::add(KeyRangeMap<int>& map, KeyRangeRef const& keys, i
 
 // Returns the sampled metric value (possibly 0, possibly increased by the sampling factor)
 int64_t TransientStorageMetricSample::addAndExpire(const Key& key, int64_t metric, double expiration) {
-	int64_t x = add(key, metric);
+	auto x = add(key, metric);
 	if (x)
-		queue.emplace_back(expiration, std::make_pair(*sample.find(key), -x));
+		queue.emplace_back(expiration, std::make_pair(key, -x));
 	return x;
 }
 
@@ -575,17 +575,18 @@ bool TransientStorageMetricSample::roll(int64_t metric) const {
 }
 
 void TransientStorageMetricSample::poll(KeyRangeMap<std::vector<PromiseStream<StorageMetrics>>>& waitMap,
-                                        StorageMetrics m) {
+                                        StorageMetrics metrics) {
 	double now = ::now();
 	while (queue.size() && queue.front().first <= now) {
 		KeyRef key = queue.front().second.first;
 		int64_t delta = queue.front().second.second;
 		ASSERT(delta != 0);
 
-		if (sample.addMetric(key, delta) == 0)
-			sample.erase(key);
+		auto [m, it] = sample.addMetric(key, delta);
+		if (m == 0)
+			sample.erase(it);
 
-		StorageMetrics deltaM = m * delta;
+		StorageMetrics deltaM = metrics * delta;
 		auto v = waitMap[key];
 		for (int i = 0; i < v.size(); i++) {
 			CODE_PROBE(true, "TransientStorageMetricSample poll update");
@@ -603,8 +604,9 @@ void TransientStorageMetricSample::poll() {
 		int64_t delta = queue.front().second.second;
 		ASSERT(delta != 0);
 
-		if (sample.addMetric(key, delta) == 0)
-			sample.erase(key);
+		auto [m, it] = sample.addMetric(key, delta);
+		if (m == 0)
+			sample.erase(it);
 
 		queue.pop_front();
 	}
@@ -621,8 +623,9 @@ int64_t TransientStorageMetricSample::add(const Key& key, int64_t metric) {
 		metric = metric < 0 ? -metricUnitsPerSample : metricUnitsPerSample;
 	}
 
-	if (sample.addMetric(key, metric) == 0)
-		sample.erase(key);
+	auto [m, it] = sample.addMetric(key, metric);
+	if (m == 0)
+		sample.erase(it);
 
 	return metric;
 }

fdbserver/include/fdbserver/StorageMetrics.actor.h

@@ -74,6 +74,8 @@ struct TransientStorageMetricSample : StorageMetricSample {
 
 private:
 	bool roll(int64_t metric) const;
+
+	// return the sampled metric delta
 	int64_t add(const Key& key, int64_t metric);
 };
 

flow/include/flow/IndexedSet.h

@@ -193,9 +193,9 @@ public:
 	int insert(const std::vector<std::pair<T, Metric>>& data, bool replaceExisting = true);
 
 	// Increase the metric for the given item by the given amount.  Inserts data into the set if it
-	//   doesn't exist. Returns the new sum.
+	//   doesn't exist. Returns the pair of new sum and inserted iterator.
 	template <class T_, class Metric_>
-	Metric addMetric(T_&& data, Metric_&& metric);
+	std::pair<Metric, iterator> addMetric(T_&& data, Metric_&& metric);
 
 	// Remove the data item, if any, which is equal to key
 	template <class Key>
@@ -820,15 +820,16 @@ typename IndexedSet<T, Metric>::template Impl<isConst>::IteratorT IndexedSet<T,
 
 template <class T, class Metric>
 template <class T_, class Metric_>
-Metric IndexedSet<T, Metric>::addMetric(T_&& data, Metric_&& metric) {
+std::pair<Metric, typename IndexedSet<T, Metric>::iterator> IndexedSet<T, Metric>::addMetric(T_&& data,
+                                                                                             Metric_&& metric) {
 	auto i = find(data);
 	if (i == end()) {
-		insert(std::forward<T_>(data), std::forward<Metric_>(metric));
-		return metric;
+		auto it = insert(std::forward<T_>(data), std::forward<Metric_>(metric));
+		return { metric, it };
 	} else {
 		Metric m = metric + getMetric(i);
-		insert(std::forward<T_>(data), m);
-		return m;
+		auto it = insert(std::forward<T_>(data), m);
+		return { m, it };
 	}
 }
 

flow/include/flow/MetricSample.h

@@ -127,14 +127,14 @@ struct TransientThresholdMetricSample : MetricSample<T> {
 			int64_t delta = std::get<2>(queue.front());
 			ASSERT(delta != 0);
 
-			int64_t val = this->sample.addMetric(T(key), delta);
+			auto [val, it] = this->sample.addMetric(T(key), delta);
 			if (val < thresholdLimit && (val + std::abs(delta)) >= thresholdLimit) {
 				auto iter = thresholdCrossedSet.find(key);
 				ASSERT(iter != thresholdCrossedSet.end());
 				thresholdCrossedSet.erase(iter);
 			}
 			if (val == 0)
-				this->sample.erase(key);
+				this->sample.erase(it);
 
 			queue.pop_front();
 		}
@@ -159,7 +159,7 @@ private:
 			metric = metric < 0 ? -this->metricUnitsPerSample : this->metricUnitsPerSample;
 		}
 
-		int64_t val = this->sample.addMetric(T(key), metric);
+		auto [val, it] = this->sample.addMetric(T(key), metric);
 		if (val >= thresholdLimit) {
 			ASSERT((val - metric) < thresholdLimit ? thresholdCrossedSet.find(key) == thresholdCrossedSet.end()
 			                                       : thresholdCrossedSet.find(key) != thresholdCrossedSet.end());
@@ -167,7 +167,7 @@ private:
 		}
 
 		if (val == 0)
-			this->sample.erase(key);
+			this->sample.erase(it);
 
 		return metric;
 	}