/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
package org.apache.hadoop.hbase.metrics.histogram;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import org.apache.hadoop.metrics.MetricsRecord;
import org.apache.hadoop.metrics.util.MetricsBase;
import org.apache.hadoop.metrics.util.MetricsRegistry;
import com.yammer.metrics.stats.Sample;
import com.yammer.metrics.stats.Snapshot;
import com.yammer.metrics.stats.UniformSample;
import com.yammer.metrics.stats.ExponentiallyDecayingSample;
public class MetricsHistogram extends MetricsBase {
// 1028 items implies 99.9% CI w/ 5% margin of error
// (assuming a normal distribution on the underlying data)
private static final int DEFAULT_SAMPLE_SIZE = 1028;
// the bias towards sampling from more recent data.
// Per Cormode et al. an alpha of 0.015 strongly biases to the last 5 minutes
private static final double DEFAULT_ALPHA = 0.015;
/**
* Constructor to create a new histogram metric
* @param nam the name to publish the metric under
* @param registry where the metrics object will be registered
* @param description the metric's description
* @param forwardBiased true if you want this histogram to give more
* weight to recent data,
* false if you want all data to have uniform weight
*/
public MetricsHistogram(final String nam, final MetricsRegistry registry,
final String description, boolean forwardBiased) {
super(nam, description);
this.min = new AtomicLong();
this.max = new AtomicLong();
this.sum = new AtomicLong();
this.sample = forwardBiased ?
new ExponentiallyDecayingSample(DEFAULT_SAMPLE_SIZE, DEFAULT_ALPHA)
: new UniformSample(DEFAULT_SAMPLE_SIZE);
this.variance = new AtomicReference<double[]>(new double[]{-1, 0});
this.count = new AtomicLong();
this.clear();
if (registry != null) {
registry.add(nam, this);
}
}
/**
* Constructor create a new (forward biased) histogram metric
* @param nam the name to publish the metric under
* @param registry where the metrics object will be registered
* @param description the metric's description
*/
public MetricsHistogram(final String nam, MetricsRegistry registry,
final String description) {
this(nam, registry, NO_DESCRIPTION, true);
}
/**
* Constructor - create a new (forward biased) histogram metric
* @param nam the name of the metrics to be used to publish the metric
* @param registry - where the metrics object will be registered
*/
public MetricsHistogram(final String nam, MetricsRegistry registry) {
this(nam, registry, NO_DESCRIPTION);
}
private final Sample sample;
private final AtomicLong min;
private final AtomicLong max;
private final AtomicLong sum;
// these are for computing a running-variance,
// without letting floating point errors accumulate via Welford's algorithm
private final AtomicReference<double[]> variance;
private final AtomicLong count;
/**
* Clears all recorded values.
*/
public void clear() {
this.sample.clear();
this.count.set(0);
this.max.set(Long.MIN_VALUE);
this.min.set(Long.MAX_VALUE);
this.sum.set(0);
variance.set(new double[]{-1, 0});
}
public void update(int val) {
update((long) val);
}
public void update(final long val) {
count.incrementAndGet();
sample.update(val);
setMax(val);
setMin(val);
sum.getAndAdd(val);
updateVariance(val);
}
private void setMax(final long potentialMax) {
boolean done = false;
while (!done) {
final long currentMax = max.get();
done = currentMax >= potentialMax
|| max.compareAndSet(currentMax, potentialMax);
}
}
private void setMin(long potentialMin) {
boolean done = false;
while (!done) {
final long currentMin = min.get();
done = currentMin <= potentialMin
|| min.compareAndSet(currentMin, potentialMin);
}
}
private void updateVariance(long value) {
boolean done = false;
while (!done) {
final double[] oldValues = variance.get();
final double[] newValues = new double[2];
if (oldValues[0] == -1) {
newValues[0] = value;
newValues[1] = 0;
} else {
final double oldM = oldValues[0];
final double oldS = oldValues[1];
final double newM = oldM + ((value - oldM) / getCount());
final double newS = oldS + ((value - oldM) * (value - newM));
newValues[0] = newM;
newValues[1] = newS;
}
done = variance.compareAndSet(oldValues, newValues);
}
}
public long getCount() {
return count.get();
}
public long getMax() {
if (getCount() > 0) {
return max.get();
}
return 0L;
}
public long getMin() {
if (getCount() > 0) {
return min.get();
}
return 0L;
}
public double getMean() {
if (getCount() > 0) {
return sum.get() / (double) getCount();
}
return 0.0;
}
public double getStdDev() {
if (getCount() > 0) {
return Math.sqrt(getVariance());
}
return 0.0;
}
public Snapshot getSnapshot() {
return sample.getSnapshot();
}
private double getVariance() {
if (getCount() <= 1) {
return 0.0;
}
return variance.get()[1] / (getCount() - 1);
}
@Override
public void pushMetric(MetricsRecord mr) {
final Snapshot s = this.getSnapshot();
mr.setMetric(getName() + "_num_ops", this.getCount());
mr.setMetric(getName() + "_min", this.getMin());
mr.setMetric(getName() + "_max", this.getMax());
mr.setMetric(getName() + "_mean", (float) this.getMean());
mr.setMetric(getName() + "_std_dev", (float) this.getStdDev());
mr.setMetric(getName() + "_median", (float) s.getMedian());
mr.setMetric(getName() + "_75th_percentile",
(float) s.get75thPercentile());
mr.setMetric(getName() + "_95th_percentile",
(float) s.get95thPercentile());
mr.setMetric(getName() + "_99th_percentile",
(float) s.get99thPercentile());
}
}