| /* |
| * 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.utils; |
| |
| import java.io.Serializable; |
| import java.util.*; |
| import java.util.concurrent.*; |
| |
| import org.apache.cassandra.concurrent.*; |
| import org.slf4j.*; |
| |
| import com.clearspring.analytics.stream.*; |
| import com.clearspring.analytics.stream.cardinality.HyperLogLogPlus; |
| import com.google.common.annotations.VisibleForTesting; |
| |
| public class TopKSampler<T> |
| { |
| private static final Logger logger = LoggerFactory.getLogger(TopKSampler.class); |
| private volatile boolean enabled = false; |
| |
| @VisibleForTesting |
| static final ThreadPoolExecutor samplerExecutor = new JMXEnabledThreadPoolExecutor(1, 1, |
| TimeUnit.SECONDS, |
| new LinkedBlockingQueue<Runnable>(), |
| new NamedThreadFactory("Sampler"), |
| "internal"); |
| |
| private StreamSummary<T> summary; |
| @VisibleForTesting |
| HyperLogLogPlus hll; |
| |
| /** |
| * Start to record samples |
| * |
| * @param capacity |
| * Number of sample items to keep in memory, the lower this is |
| * the less accurate results are. For best results use value |
| * close to cardinality, but understand the memory trade offs. |
| */ |
| public synchronized void beginSampling(int capacity) |
| { |
| if (!enabled) |
| { |
| summary = new StreamSummary<T>(capacity); |
| hll = new HyperLogLogPlus(14); |
| enabled = true; |
| } |
| } |
| |
| /** |
| * Call to stop collecting samples, and gather the results |
| * @param count Number of most frequent items to return |
| */ |
| public synchronized SamplerResult<T> finishSampling(int count) |
| { |
| List<Counter<T>> results = Collections.EMPTY_LIST; |
| long cardinality = 0; |
| if (enabled) |
| { |
| enabled = false; |
| results = summary.topK(count); |
| cardinality = hll.cardinality(); |
| } |
| return new SamplerResult<T>(results, cardinality); |
| } |
| |
| public void addSample(T item) |
| { |
| addSample(item, item.hashCode(), 1); |
| } |
| |
| /** |
| * Adds a sample to statistics collection. This method is non-blocking and will |
| * use the "Sampler" thread pool to record results if the sampler is enabled. If not |
| * sampling this is a NOOP |
| */ |
| public void addSample(final T item, final long hash, final int value) |
| { |
| if (enabled) |
| { |
| final Object lock = this; |
| samplerExecutor.execute(new Runnable() |
| { |
| public void run() |
| { |
| // samplerExecutor is single threaded but still need |
| // synchronization against jmx calls to finishSampling |
| synchronized (lock) |
| { |
| if (enabled) |
| { |
| try |
| { |
| summary.offer(item, value); |
| hll.offerHashed(hash); |
| } catch (Exception e) |
| { |
| logger.trace("Failure to offer sample", e); |
| } |
| } |
| } |
| } |
| }); |
| } |
| } |
| |
| /** |
| * Represents the cardinality and the topK ranked items collected during a |
| * sample period |
| */ |
| public static class SamplerResult<S> implements Serializable |
| { |
| public final List<Counter<S>> topK; |
| public final long cardinality; |
| |
| public SamplerResult(List<Counter<S>> topK, long cardinality) |
| { |
| this.topK = topK; |
| this.cardinality = cardinality; |
| } |
| } |
| |
| } |
| |