text: /*
   * Licensed to Crate under one or more contributor license agreements.
   * See the NOTICE file distributed with this work for additional
   * information regarding copyright ownership.  Crate 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.
   *
   * However, if you have executed another commercial license agreement
   * with Crate these terms will supersede the license and you may use the
   * software solely pursuant to the terms of the relevant commercial
   * agreement.
   */
  
  package io.crate.metadata.sys;
  
  import io.crate.planner.operators.StatementClassifier.Classification;
  import org.HdrHistogram.Histogram;
  import org.HdrHistogram.Recorder;
  
  import java.util.Iterator;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.LongAdder;
  
  public class ClassifiedMetrics implements Iterable<MetricsView> {
  
      private static final long HIGHEST_TRACKABLE_VALUE = TimeUnit.MINUTES.toMillis(10);
      private static final int NUMBER_OF_SIGNIFICANT_VALUE_DIGITS = 3;
  
      private final ConcurrentHashMap<Classification, Metrics> metrics = new ConcurrentHashMap<>();
  
      public static class Metrics {
  
          private final Classification classification;
          private final LongAdder sumOfDurations = new LongAdder();
          private final LongAdder failedCount = new LongAdder();
          private final Recorder recorder;
  
          private final Histogram totalHistogram = new Histogram(HIGHEST_TRACKABLE_VALUE, NUMBER_OF_SIGNIFICANT_VALUE_DIGITS);
  
          public Metrics(Classification classification) {
              this.classification = classification;
              this.recorder = new Recorder(HIGHEST_TRACKABLE_VALUE, NUMBER_OF_SIGNIFICANT_VALUE_DIGITS);
          }
  
          public void recordValue(long duration) {
              // We use start and end time to calculate the duration (since we track them anyway)
              // If the system time is adjusted this can lead to negative durations
              // so we protect here against it.
              recorder.recordValue(Math.min(Math.max(0, duration), HIGHEST_TRACKABLE_VALUE));
              // we record the real duration (with no upper capping) in the sum of durations as there are no upper limits
              // for the values we record as it is the case with the histogram
              sumOfDurations.add(Math.max(0, duration));
          }
  
          public void recordFailedExecution(long duration) {
              recordValue(duration);
              failedCount.increment();
          }
  
          public MetricsView createMetricsView() {
              Histogram histogram;
              synchronized (totalHistogram) {
                  // getIntervalHistogram resets the internal histogram afterwards;
                  // so we keep `totalHistogram` to not lose any measurements.
                  Histogram intervalHistogram = recorder.getIntervalHistogram();
                  totalHistogram.add(intervalHistogram);
                  histogram = totalHistogram.copy();
              }
              return new MetricsView(
                  histogram,
                  sumOfDurations.longValue(),
                  failedCount.longValue(),
                  classification
              );
          }
      }
  
      public void recordValue(Classification classification, long duration) {
          getOrCreate(classification).recordValue(duration);
      }
  
      public void recordFailedExecution(Classification classification, long duration) {
          getOrCreate(classification).recordFailedExecution(duration);
      }
  
      private Metrics getOrCreate(Classification classification) {
          Metrics histogram = metrics.get(classification);
          if (histogram == null) {
              histogram = new Metrics(classification);
              metrics.put(classification, histogram);
          }
          return histogram;
      }
  
      public void reset() {
          metrics.clear();
      }
  
      @Override
      public Iterator<MetricsView> iterator() {
          return metrics.values()
              .stream()
              .map(Metrics::createMetricsView)
              .iterator();
      }
  }
  