foundationdb/flow/Histogram.cpp

/*
 * Histogram.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 <flow/Histogram.h>
#include <flow/flow.h>
#include <flow/UnitTest.h>
// TODO: remove dependency on fdbrpc.

// we need to be able to check if we're in simulation so that the histograms are properly
// scoped to the right "machine".
// either we pull g_simulator into flow, or flow (and the I/O path) will be unable to log performance
// metrics.
#include <limits>

#pragma region HistogramRegistry

HistogramRegistry& GetHistogramRegistry() {
	auto h = g_network->global(INetwork::enHistogram);

	if (h) {
		return *reinterpret_cast<HistogramRegistry*>(h);
	} else {
		auto res = new HistogramRegistry();
		g_network->setGlobal(INetwork::enHistogram, res);
		return *res;
	}
}

void HistogramRegistry::registerHistogram(Histogram* h) {
	if (histograms.find(h->name()) != histograms.end()) {
		TraceEvent(SevError, "HistogramDoubleRegistered").detail("group", h->group).detail("op", h->op);
		ASSERT(false);
	}
	histograms.insert(std::pair<std::string, Histogram*>(h->name(), h));
}

void HistogramRegistry::unregisterHistogram(Histogram* h) {
	std::string name = h->name();
	if (histograms.find(name) == histograms.end()) {
		TraceEvent(SevError, "HistogramNotRegistered").detail("group", h->group).detail("op", h->op);
	}
	int count = histograms.erase(name);
	ASSERT(count == 1);
}

Histogram* HistogramRegistry::lookupHistogram(std::string const& name) {
	auto h = histograms.find(name);
	if (h == histograms.end()) {
		return nullptr;
	}
	return h->second;
}

void HistogramRegistry::logReport(double elapsed) {
	for (auto& i : histograms) {
		// Reset all buckets in writeToLog function
		i.second->writeToLog(elapsed);
	}
}

void HistogramRegistry::clear() {
	for (auto& i : histograms) {
		i.second->clear();
	}
}

#pragma endregion // HistogramRegistry

#pragma region Histogram

const char* const Histogram::UnitToStringMapper[] = { "milliseconds", "bytes", "bytes_per_second",
	                                                  "percentage",   "count", "none" };

void Histogram::writeToLog(double elapsed) {
	bool active = false;
	for (uint32_t i = 0; i < 32; i++) {
		if (buckets[i]) {
			active = true;
			break;
		}
	}
	if (!active) {
		return;
	}

	TraceEvent e(SevInfo, "Histogram");
	e.detail("Group", group).detail("Op", op).detail("Unit", UnitToStringMapper[(size_t)unit]);
	if (elapsed > 0)
		e.detail("Elapsed", elapsed);
	int totalCount = 0;
	for (uint32_t i = 0; i < 32; i++) {
		uint64_t value = uint64_t(1) << (i + 1);

		if (buckets[i]) {
			totalCount += buckets[i];
			switch (unit) {
			case Unit::milliseconds:
				// value stored in microseconds, so divide by 1000 before writing
				e.detail(format("LessThan%u.%03u", int(value / 1000), int(value % 1000)), buckets[i]);
				break;
			case Unit::bytes:
			case Unit::bytes_per_second:
				e.detail(format("LessThan%" PRIu64, value), buckets[i]);
				break;
			case Unit::percentageLinear:
				e.detail(format("LessThan%f", (i + 1) * 0.04), buckets[i]);
				break;
			case Unit::countLinear:
				value = uint64_t((i + 1) * ((upperBound - lowerBound) / 31.0));
				e.detail(format("LessThan%" PRIu64, value), buckets[i]);
				break;
			case Unit::MAXHISTOGRAMUNIT:
				e.detail(format("Default%u", i), buckets[i]);
				break;
			default:
				ASSERT(false);
			}
		}
	}
	e.detail("TotalCount", totalCount);
	clear();
}

std::string Histogram::drawHistogram() {

	std::stringstream result;

	const char* verticalLine = "├\0";
	const char* origin = "└\0";
	const char* emptyCell = "------\0";
	const char* halfCell = "---▄▄▄\0";
	const char* fullCell = "---███\0";
	const char* xFull = "---▀▀▀\0";
	const char* xEmpty = "------\0";
	const char* lineEnd = "--- \0";
	const unsigned int width = std::strlen(emptyCell);

	int max_lines = 23;
	uint32_t total = 0;
	double maxPct = 0;

	for (int i = 0; i < 32; i++) {
		total += buckets[i];
	}
	for (int i = 0; i < 32; i++) {
		maxPct = std::max(maxPct, (100.0 * buckets[i]) / total);
	}

	double intervalSize = (maxPct < (max_lines - 3)) ? 1 : maxPct / (max_lines - 3);
	unsigned int lines = (maxPct < (max_lines - 3)) ? (unsigned int)maxPct : (max_lines - 3);

	result << "Total Inputs: " << total << std::fixed << "\n";
	result << "Percent"
	       << "\n";
	for (int l = 0; l < lines; l++) {
		double currHeight = (lines - l) * intervalSize;
		double halfFullHeight = currHeight - intervalSize / 4;
		result << std::setw(6) << std::setprecision(2) << currHeight << " " << verticalLine;
		for (int i = 0; i < 32; i++) {
			double pct = (100.0 * buckets[i]) / total;
			if (pct > currHeight)
				result << fullCell;
			else if (pct > halfFullHeight)
				result << halfCell;
			else
				result << emptyCell;
		}
		result << lineEnd << "\n";
	}

	result << "  0.00 " << origin;
	for (int i = 0; i < 32; i++) {
		double pct = (100.0 * buckets[i]) / total;
		if (pct > intervalSize / 4)
			result << xFull;
		else
			result << xEmpty;
	}
	result << lineEnd << "\n";

	result << std::string(9, ' ');
	for (int i = 0; i < 32; i++) {
		result << std::left << std::setw(width) << "  B" + std::to_string(i);
	}
	result << "\n";
	return result.str();
}

#pragma endregion // Histogram

TEST_CASE("/flow/histogram/smoke_test") {
	{
		Reference<Histogram> h = Histogram::getHistogram("smoke_test"_sr, "counts"_sr, Histogram::Unit::bytes);

		h->sample(0);
		ASSERT(h->buckets[0] == 1);
		h->sample(1);
		ASSERT(h->buckets[0] == 2);

		h->sample(2);
		ASSERT(h->buckets[1] == 1);

		GetHistogramRegistry().logReport();

		ASSERT(h->buckets[0] == 0);
		h->sample(0);
		ASSERT(h->buckets[0] == 1);
		h = Histogram::getHistogram("smoke_test"_sr, "counts2"_sr, Histogram::Unit::bytes);

		// confirm that old h was deallocated.
		h = Histogram::getHistogram("smoke_test"_sr, "counts"_sr, Histogram::Unit::bytes);
		ASSERT(h->buckets[0] == 0);

		h = Histogram::getHistogram("smoke_test"_sr, "times"_sr, Histogram::Unit::milliseconds);

		h->sampleSeconds(0.000000);
		h->sampleSeconds(0.0000019);
		ASSERT(h->buckets[0] == 2);
		h->sampleSeconds(0.0000021);
		ASSERT(h->buckets[1] == 1);
		h->sampleSeconds(0.000015);
		ASSERT(h->buckets[3] == 1);

		h->sampleSeconds(4400.0);
		ASSERT(h->buckets[31] == 1);

		GetHistogramRegistry().logReport();
	}

	// h has been deallocated.  Does this crash?
	GetHistogramRegistry().logReport();

	return Void();
}