| /* |
| * 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.Collections; |
| import java.util.List; |
| import java.util.stream.Collectors; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| import com.clearspring.analytics.stream.StreamSummary; |
| |
| import static java.util.concurrent.TimeUnit.MILLISECONDS; |
| |
| /** |
| * Find the most frequent sample. A sample adds to the sum of its key ie |
| * <p>add("x", 10); and add("x", 20); will result in "x" = 30</p> This uses StreamSummary to only store the |
| * approximate cardinality (capacity) of keys. If the number of distinct keys exceed the capacity, the error of the |
| * sample may increase depending on distribution of keys among the total set. |
| * |
| * @param <T> |
| */ |
| public abstract class FrequencySampler<T> extends Sampler<T> |
| { |
| private static final Logger logger = LoggerFactory.getLogger(FrequencySampler.class); |
| private long endTimeNanos = -1; |
| |
| private StreamSummary<T> summary; |
| |
| /** |
| * 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, int durationMillis) |
| { |
| if (endTimeNanos == -1 || clock.now() > endTimeNanos) |
| { |
| summary = new StreamSummary<>(capacity); |
| endTimeNanos = clock.now() + MILLISECONDS.toNanos(durationMillis); |
| } |
| else |
| throw new RuntimeException("Sampling already in progress"); |
| } |
| |
| /** |
| * Call to stop collecting samples, and gather the results |
| * @param count Number of most frequent items to return |
| */ |
| public synchronized List<Sample<T>> finishSampling(int count) |
| { |
| List<Sample<T>> results = Collections.emptyList(); |
| if (endTimeNanos != -1) |
| { |
| endTimeNanos = -1; |
| results = summary.topK(count) |
| .stream() |
| .map(c -> new Sample<T>(c.getItem(), c.getCount(), c.getError())) |
| .collect(Collectors.toList()); |
| } |
| return results; |
| } |
| |
| protected synchronized void insert(final T item, final long value) |
| { |
| // samplerExecutor is single threaded but still need |
| // synchronization against jmx calls to finishSampling |
| if (value > 0 && clock.now() <= endTimeNanos) |
| { |
| try |
| { |
| summary.offer(item, (int) Math.min(value, Integer.MAX_VALUE)); |
| } catch (Exception e) |
| { |
| logger.trace("Failure to offer sample", e); |
| } |
| } |
| } |
| |
| public boolean isEnabled() |
| { |
| return endTimeNanos != -1 && clock.now() <= endTimeNanos; |
| } |
| |
| } |
| |