| /* |
| * 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.cassandra.metrics; |
| |
| |
| import java.util.concurrent.TimeUnit; |
| import java.util.concurrent.atomic.AtomicLong; |
| |
| import static java.lang.Math.exp; |
| import com.codahale.metrics.Clock; |
| |
| /** |
| * A meter metric which measures mean throughput as well as fifteen-minute and two-hour |
| * exponentially-weighted moving average throughputs. |
| * |
| * This is based heavily on the Meter and EWMA classes from codahale/yammer metrics. |
| * |
| * @see <a href="http://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average">EMA</a> |
| */ |
| public class RestorableMeter |
| { |
| private static final long TICK_INTERVAL = TimeUnit.SECONDS.toNanos(5); |
| private static final double NANOS_PER_SECOND = TimeUnit.SECONDS.toNanos(1); |
| |
| private final RestorableEWMA m15Rate; |
| private final RestorableEWMA m120Rate; |
| |
| private final AtomicLong count = new AtomicLong(); |
| private final long startTime; |
| private final AtomicLong lastTick; |
| private final Clock clock = Clock.defaultClock(); |
| |
| /** |
| * Creates a new, uninitialized RestorableMeter. |
| */ |
| public RestorableMeter() { |
| this.m15Rate = new RestorableEWMA(TimeUnit.MINUTES.toSeconds(15)); |
| this.m120Rate = new RestorableEWMA(TimeUnit.MINUTES.toSeconds(120)); |
| this.startTime = this.clock.getTick(); |
| this.lastTick = new AtomicLong(startTime); |
| } |
| |
| /** |
| * Restores a RestorableMeter from the last seen 15m and 2h rates. |
| * @param lastM15Rate the last-seen 15m rate, in terms of events per second |
| * @param lastM120Rate the last seen 2h rate, in terms of events per second |
| */ |
| public RestorableMeter(double lastM15Rate, double lastM120Rate) { |
| this.m15Rate = new RestorableEWMA(lastM15Rate, TimeUnit.MINUTES.toSeconds(15)); |
| this.m120Rate = new RestorableEWMA(lastM120Rate, TimeUnit.MINUTES.toSeconds(120)); |
| this.startTime = this.clock.getTick(); |
| this.lastTick = new AtomicLong(startTime); |
| } |
| |
| /** |
| * Updates the moving averages as needed. |
| */ |
| private void tickIfNecessary() { |
| final long oldTick = lastTick.get(); |
| final long newTick = clock.getTick(); |
| final long age = newTick - oldTick; |
| if (age > TICK_INTERVAL) { |
| final long newIntervalStartTick = newTick - age % TICK_INTERVAL; |
| if (lastTick.compareAndSet(oldTick, newIntervalStartTick)) { |
| final long requiredTicks = age / TICK_INTERVAL; |
| for (long i = 0; i < requiredTicks; i++) { |
| m15Rate.tick(); |
| m120Rate.tick(); |
| } |
| } |
| } |
| } |
| |
| /** |
| * Mark the occurrence of an event. |
| */ |
| public void mark() { |
| mark(1); |
| } |
| |
| /** |
| * Mark the occurrence of a given number of events. |
| * |
| * @param n the number of events |
| */ |
| public void mark(long n) { |
| tickIfNecessary(); |
| count.addAndGet(n); |
| m15Rate.update(n); |
| m120Rate.update(n); |
| } |
| |
| /** |
| * Returns the 15-minute rate in terms of events per second. This carries the previous rate when restored. |
| */ |
| public double fifteenMinuteRate() { |
| tickIfNecessary(); |
| return m15Rate.rate(); |
| } |
| |
| /** |
| * Returns the two-hour rate in terms of events per second. This carries the previous rate when restored. |
| */ |
| public double twoHourRate() { |
| tickIfNecessary(); |
| return m120Rate.rate(); |
| } |
| |
| /** |
| * The total number of events that have occurred since this object was created. Note that the previous count |
| * is *not* carried over when a RestorableMeter is restored. |
| */ |
| public long count() { |
| return count.get(); |
| } |
| |
| /** |
| * Returns the mean rate of events per second since this object was created. Note that the mean rate |
| * does *not* carry over when a RestorableMeter is restored, so the mean rate is only a measure since |
| * this object was created. |
| */ |
| public double meanRate() { |
| if (count() == 0) { |
| return 0.0; |
| } else { |
| final long elapsed = (clock.getTick() - startTime); |
| return (count() / (double) elapsed) * NANOS_PER_SECOND; |
| } |
| } |
| |
| static class RestorableEWMA { |
| private volatile boolean initialized = false; |
| private volatile double rate = 0.0; // average rate in terms of events per nanosecond |
| |
| private final AtomicLong uncounted = new AtomicLong(); |
| private final double alpha, interval; |
| |
| /** |
| * Create a new, uninitialized EWMA with a given window. |
| * |
| * @param windowInSeconds the window of time this EWMA should average over, expressed as a number of seconds |
| */ |
| public RestorableEWMA(long windowInSeconds) { |
| this.alpha = 1 - exp((-TICK_INTERVAL / NANOS_PER_SECOND) / windowInSeconds); |
| this.interval = TICK_INTERVAL; |
| } |
| |
| /** |
| * Restore an EWMA from a last-seen rate and a given window. |
| * |
| * @param intervalInSeconds the window of time this EWMA should average over, expressed as a number of seconds |
| */ |
| public RestorableEWMA(double lastRate, long intervalInSeconds) { |
| this(intervalInSeconds); |
| this.rate = lastRate / NANOS_PER_SECOND; |
| this.initialized = true; |
| } |
| |
| /** |
| * Update the moving average with a new value. |
| */ |
| public void update(long n) { |
| uncounted.addAndGet(n); |
| } |
| |
| /** |
| * Mark the passage of time and decay the current rate accordingly. |
| */ |
| public void tick() { |
| final long count = uncounted.getAndSet(0); |
| final double instantRate = count / interval; |
| if (initialized) { |
| rate += (alpha * (instantRate - rate)); |
| } else { |
| rate = instantRate; |
| initialized = true; |
| } |
| } |
| |
| /** |
| * Returns the rate in terms of events per second. |
| */ |
| public double rate() { |
| return rate * NANOS_PER_SECOND; |
| } |
| } |
| } |