foundationdb/fdbserver/TransactionTagCounter.cpp

/*
 * TransactionTagCounter.cpp
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2022 Apple Inc. and the FoundationDB project authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "fdbserver/Knobs.h"
#include "fdbserver/TransactionTagCounter.h"
#include "flow/Trace.h"

namespace {

class TopKTags {
public:
	struct TagAndCount {
		TransactionTag tag;
		int64_t count;
		bool operator<(TagAndCount const& other) const { return count < other.count; }
		explicit TagAndCount(TransactionTag tag, int64_t count) : tag(tag), count(count) {}
	};

private:
	// Because the number of tracked is expected to be small, they can be tracked
	// in a simple vector. If the number of tracked tags increases, a more sophisticated
	// data structure will be required.
	std::vector<TagAndCount> topTags;
	int limit;

public:
	explicit TopKTags(int limit) : limit(limit) {
		ASSERT_GT(limit, 0);
		topTags.reserve(limit);
	}

	void incrementCount(TransactionTag tag, int previousCount, int increase) {
		auto iter = std::find_if(topTags.begin(), topTags.end(), [tag](const auto& tc) { return tc.tag == tag; });
		if (iter != topTags.end()) {
			ASSERT_EQ(previousCount, iter->count);
			iter->count += increase;
		} else if (topTags.size() < limit) {
			ASSERT_EQ(previousCount, 0);
			topTags.emplace_back(tag, increase);
		} else {
			auto toReplace = std::min_element(topTags.begin(), topTags.end());
			ASSERT_GE(toReplace->count, previousCount);
			if (toReplace->count < previousCount + increase) {
				toReplace->tag = tag;
				toReplace->count = previousCount + increase;
			}
		}
	}

	std::vector<StorageQueuingMetricsReply::TagInfo> getBusiestTags(double elapsed, double totalSampleCount) const {
		std::vector<StorageQueuingMetricsReply::TagInfo> result;
		for (auto const& tagAndCounter : topTags) {
			auto rate = (tagAndCounter.count / CLIENT_KNOBS->READ_TAG_SAMPLE_RATE) / elapsed;
			if (rate > SERVER_KNOBS->MIN_TAG_READ_PAGES_RATE) {
				result.emplace_back(tagAndCounter.tag, rate, tagAndCounter.count / totalSampleCount);
			}
		}
		return result;
	}

	void clear() { topTags.clear(); }
};

} // namespace

class TransactionTagCounterImpl {
	UID thisServerID;
	TransactionTagMap<int64_t> intervalCounts;
	int64_t intervalTotalSampledCount = 0;
	TopKTags topTags;
	double intervalStart = 0;

	std::vector<StorageQueuingMetricsReply::TagInfo> previousBusiestTags;
	Reference<EventCacheHolder> busiestReadTagEventHolder;

	static int64_t costFunction(int64_t bytes) { return bytes / SERVER_KNOBS->READ_COST_BYTE_FACTOR + 1; }

public:
	TransactionTagCounterImpl(UID thisServerID)
	  : thisServerID(thisServerID), topTags(SERVER_KNOBS->SS_THROTTLE_TAGS_TRACKED),
	    busiestReadTagEventHolder(makeReference<EventCacheHolder>(thisServerID.toString() + "/BusiestReadTag")) {}

	void addRequest(Optional<TagSet> const& tags, int64_t bytes) {
		if (tags.present()) {
			CODE_PROBE(true, "Tracking transaction tag in counter");
			double cost = costFunction(bytes);
			for (auto& tag : tags.get()) {
				int64_t& count = intervalCounts[TransactionTag(tag, tags.get().getArena())];
				topTags.incrementCount(tag, count, cost);
				count += cost;
			}

			intervalTotalSampledCount += cost;
		}
	}

	void startNewInterval() {
		double elapsed = now() - intervalStart;
		previousBusiestTags.clear();
		if (intervalStart > 0 && CLIENT_KNOBS->READ_TAG_SAMPLE_RATE > 0 && elapsed > 0) {
			previousBusiestTags = topTags.getBusiestTags(elapsed, intervalTotalSampledCount);

			// For status, report the busiest tag:
			if (previousBusiestTags.empty()) {
				TraceEvent("BusiestReadTag", thisServerID).detail("TagCost", 0);
			} else {
				auto busiestTagInfo = previousBusiestTags[0];
				for (int i = 1; i < previousBusiestTags.size(); ++i) {
					auto const& tagInfo = previousBusiestTags[i];
					if (tagInfo.rate > busiestTagInfo.rate) {
						busiestTagInfo = tagInfo;
					}
				}
				TraceEvent("BusiestReadTag", thisServerID)
				    .detail("Tag", printable(busiestTagInfo.tag))
				    .detail("TagCost", busiestTagInfo.rate)
				    .detail("FractionalBusyness", busiestTagInfo.fractionalBusyness);
			}

			for (const auto& tagInfo : previousBusiestTags) {
				TraceEvent("BusyReadTag", thisServerID)
				    .detail("Tag", printable(tagInfo.tag))
				    .detail("TagCost", tagInfo.rate)
				    .detail("FractionalBusyness", tagInfo.fractionalBusyness);
			}
		}

		intervalCounts.clear();
		intervalTotalSampledCount = 0;
		topTags.clear();
		intervalStart = now();
	}

	std::vector<StorageQueuingMetricsReply::TagInfo> const& getBusiestTags() const { return previousBusiestTags; }
};

TransactionTagCounter::TransactionTagCounter(UID thisServerID)
  : impl(PImpl<TransactionTagCounterImpl>::create(thisServerID)) {}

TransactionTagCounter::~TransactionTagCounter() = default;

void TransactionTagCounter::addRequest(Optional<TagSet> const& tags, int64_t bytes) {
	return impl->addRequest(tags, bytes);
}

void TransactionTagCounter::startNewInterval() {
	return impl->startNewInterval();
}

std::vector<StorageQueuingMetricsReply::TagInfo> const& TransactionTagCounter::getBusiestTags() const {
	return impl->getBusiestTags();
}

TEST_CASE("/TransactionTagCounter/TopKTags") {
	TopKTags topTags(2);

	// Ensure that costs are larger enough to show up
	auto const costMultiplier =
	    std::max<double>(1.0, 2 * SERVER_KNOBS->MIN_TAG_READ_PAGES_RATE * CLIENT_KNOBS->READ_TAG_SAMPLE_RATE);

	ASSERT_EQ(topTags.getBusiestTags(1.0, 0).size(), 0);
	topTags.incrementCount("a"_sr, 0, 1 * costMultiplier);
	{
		auto const busiestTags = topTags.getBusiestTags(1.0, 1 * costMultiplier);
		ASSERT_EQ(busiestTags.size(), 1);
		ASSERT_EQ(std::count_if(busiestTags.begin(),
		                        busiestTags.end(),
		                        [](auto const& tagInfo) { return tagInfo.tag == "a"_sr; }),
		          1);
	}
	topTags.incrementCount("b"_sr, 0, 2 * costMultiplier);
	topTags.incrementCount("c"_sr, 0, 3 * costMultiplier);
	{
		auto busiestTags = topTags.getBusiestTags(1.0, 6 * costMultiplier);
		ASSERT_EQ(busiestTags.size(), 2);
		ASSERT_EQ(std::count_if(busiestTags.begin(),
		                        busiestTags.end(),
		                        [](auto const& tagInfo) { return tagInfo.tag == "a"_sr; }),
		          0);
		ASSERT_EQ(std::count_if(busiestTags.begin(),
		                        busiestTags.end(),
		                        [](auto const& tagInfo) { return tagInfo.tag == "b"_sr; }),
		          1);
		ASSERT_EQ(std::count_if(busiestTags.begin(),
		                        busiestTags.end(),
		                        [](auto const& tagInfo) { return tagInfo.tag == "c"_sr; }),
		          1);
	}
	topTags.incrementCount("a"_sr, 1 * costMultiplier, 3 * costMultiplier);
	{
		auto busiestTags = topTags.getBusiestTags(1.0, 9 * costMultiplier);
		ASSERT_EQ(busiestTags.size(), 2);
		ASSERT_EQ(std::count_if(busiestTags.begin(),
		                        busiestTags.end(),
		                        [](auto const& tagInfo) { return tagInfo.tag == "a"_sr; }),
		          1);
		ASSERT_EQ(std::count_if(busiestTags.begin(),
		                        busiestTags.end(),
		                        [](auto const& tagInfo) { return tagInfo.tag == "b"_sr; }),
		          0);
		ASSERT_EQ(std::count_if(busiestTags.begin(),
		                        busiestTags.end(),
		                        [](auto const& tagInfo) { return tagInfo.tag == "c"_sr; }),
		          1);
	}
	topTags.clear();
	ASSERT_EQ(topTags.getBusiestTags(1.0, 0).size(), 0);
	return Void();
}