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August 28, 2017 22:34
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What happens when we add new buckets to a Prometheus Histogram dynamically?
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package io.micrometer.core.samples; | |
import com.sun.net.httpserver.HttpServer; | |
import java.io.IOException; | |
import java.io.OutputStream; | |
import java.net.InetSocketAddress; | |
import java.util.Map; | |
import java.util.TreeMap; | |
import java.util.concurrent.atomic.DoubleAdder; | |
import java.util.stream.Collectors; | |
public class TempPrometheusVaryingHistogram { | |
DoubleAdder count = new DoubleAdder(); | |
DoubleAdder sum = new DoubleAdder(); | |
TreeMap<Double, DoubleAdder> buckets = new TreeMap<>(); | |
DoubleAdder currentValue = new DoubleAdder(); | |
public static void main(String[] args) { | |
new TempPrometheusVaryingHistogram().run(); | |
} | |
public void record(double value) { | |
count.add(1); | |
sum.add(value); | |
buckets.tailMap(value).forEach((bucket, bucketCount) -> bucketCount.add(1)); | |
} | |
public String scrape() { | |
return "# HELP summary \n" + | |
"# TYPE summary histogram\n" + | |
"summary_count " + count.sum() + "\n" + | |
"summary_sum" + sum.sum() + "\n" + | |
buckets.entrySet().stream() | |
.map(entry -> "summary_bucket{le=\"" + entry.getKey() + "\",} " + entry.getValue()) | |
.collect(Collectors.joining("\n")) + "\n\n" + | |
// so we have a sense of where the current value used for recording is | |
"# HELP curValue \n" + | |
"# TYPE curValue gauge\n" + | |
"curValue " + currentValue.sum() + "\n"; | |
} | |
// add a new bucket, initializing it's value to be equal to that of the bucket that immediately precedes it | |
public void addBucket(double bucket) { | |
DoubleAdder initialValue = new DoubleAdder(); | |
Map.Entry<Double, DoubleAdder> floor = buckets.floorEntry(bucket); | |
if(floor != null) | |
initialValue.add(floor.getValue().sum()); | |
buckets.put(bucket, initialValue); | |
} | |
@SuppressWarnings("Duplicates") | |
public void run() { | |
addBucket(1); | |
addBucket(2); | |
addBucket(3); | |
currentValue.add(2.5); | |
try { | |
HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0); | |
server.createContext("/prometheus", httpExchange -> { | |
record(currentValue.sum()); | |
currentValue.add(0.1); | |
// as we sample higher and higher values, we keep adding buckets | |
if(currentValue.sum() > buckets.lastEntry().getKey()) { | |
addBucket(buckets.lastEntry().getKey() + 1); | |
} | |
String scrape = scrape(); | |
httpExchange.sendResponseHeaders(200, scrape.length()); | |
OutputStream os = httpExchange.getResponseBody(); | |
os.write(scrape.getBytes()); | |
os.close(); | |
}); | |
new Thread(server::start).run(); | |
} catch (IOException e) { | |
throw new RuntimeException(e); | |
} | |
} | |
} |
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