content: /*
   * 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.io.PrintStream;
  import java.io.Serializable;
  import java.util.List;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.function.BiFunction;
  
  import org.apache.cassandra.concurrent.ExecutorPlus;
  import org.apache.cassandra.net.MessagingService;
  import org.apache.cassandra.net.Verb;
  import org.apache.cassandra.utils.ExecutorUtils;
  import org.apache.cassandra.utils.MonotonicClock;
  
  import com.google.common.annotations.VisibleForTesting;
  
  import static org.apache.cassandra.concurrent.ExecutorFactory.Global.executorFactory;
  
  public abstract class Sampler<T>
  {
      private static long DISABLED = -1L;
  
      private static final BiFunction<SamplerType, SamplingManager.ResultBuilder, SamplingManager.ResultBuilder>
          FrequencySamplerFomatter = (type, resultBuilder) ->
                                     resultBuilder.forType(type, type.description)
                                                  .addColumn("Table", "table")
                                                  .addColumn("Partition", "value")
                                                  .addColumn("Count", "count")
                                                  .addColumn("+/-", "error");
  
      public enum SamplerType
      {
          READS("Frequency of reads by partition", FrequencySamplerFomatter),
          WRITES("Frequency of writes by partition", FrequencySamplerFomatter),
          LOCAL_READ_TIME("Longest read query times", ((samplerType, resultBuilder) ->
                                                       resultBuilder.forType(samplerType, samplerType.description)
                                                                    .addColumn("Query", "value")
                                                                    .addColumn("Microseconds", "count"))),
          READ_ROW_COUNT("Partitions read with the most rows", ((samplerType, resultBuilder) ->
                                                        resultBuilder.forType(samplerType, samplerType.description)
                                                        .addColumn("Table", "table")
                                                        .addColumn("Partition", "value")
                                                        .addColumn("Rows", "count"))),
  
          READ_TOMBSTONE_COUNT("Partitions read with the most tombstones", ((samplerType, resultBuilder) ->
                                                        resultBuilder.forType(samplerType, samplerType.description)
                                                                     .addColumn("Table", "table")
                                                                     .addColumn("Partition", "value")
                                                                     .addColumn("Tombstones", "count"))),
  
          READ_SSTABLE_COUNT("Partitions read with the most sstables", ((samplerType, resultBuilder) ->
                                                                        resultBuilder.forType(samplerType, samplerType.description)
                                                                                     .addColumn("Table", "table")
                                                                                     .addColumn("Partition", "value")
                                                                                     .addColumn("SSTables", "count"))),
          WRITE_SIZE("Max mutation size by partition", ((samplerType, resultBuilder) ->
                                                        resultBuilder.forType(samplerType, samplerType.description)
                                                                     .addColumn("Table", "table")
                                                                     .addColumn("Partition", "value")
                                                                     .addColumn("Bytes", "count"))),
          CAS_CONTENTIONS("Frequency of CAS contention by partition", FrequencySamplerFomatter);
  
          private final String description;
          private final BiFunction<SamplerType, SamplingManager.ResultBuilder, SamplingManager.ResultBuilder> formatter;
  
          SamplerType(String description, BiFunction<SamplerType, SamplingManager.ResultBuilder, SamplingManager.ResultBuilder> formatter)
          {
              this.description = description;
              this.formatter = formatter;
          }
  
          void format(SamplingManager.ResultBuilder resultBuilder, PrintStream ps)
          {
              formatter.apply(this, resultBuilder).print(ps);
          }
      }
  
      @VisibleForTesting
      MonotonicClock clock = MonotonicClock.Global.approxTime;
  
      @VisibleForTesting
      public static final ExecutorPlus samplerExecutor = executorFactory()
              .withJmxInternal()
              .configureSequential("Sampler")
              .withQueueLimit(1000)
              .withRejectedExecutionHandler((runnable, executor) -> MessagingService.instance().metrics.recordSelfDroppedMessage(Verb._SAMPLE))
              .build();
  
      private long endTimeNanos = -1;
  
      public void addSample(final T item, final int value)
      {
          if (isEnabled())
              samplerExecutor.submit(() -> insert(item, value));
      }
  
      protected abstract void insert(T item, long value);
  
      /**
       * A sampler is enabled between {@link this#beginSampling} and {@link this#finishSampling}
       * @return true if the sampler is enabled.
       */
      public boolean isEnabled()
      {
          return endTimeNanos != DISABLED;
      }
  
      public void disable()
      {
          endTimeNanos = DISABLED;
      }
  
      /**
       * @return true if the sampler is active.
       * A sampler is active only if it is enabled and the current time is within the `durationMillis` when beginning sampling.
       */
      public boolean isActive()
      {
          return isEnabled() && clock.now() <= endTimeNanos;
      }
  
      /**
       * Update the end time for the sampler. Implicitly, calling this method enables the sampler.
       */
      public void updateEndTime(long endTimeMillis)
      {
          this.endTimeNanos = endTimeMillis;
      }
  
      /**
       * Begin sampling with the configured capacity and duration
       * @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.
       * @param durationMillis Upperbound duration in milliseconds for sampling. The sampler
       *                       stops accepting new samples after exceeding the duration
       *                       even if {@link #finishSampling(int)}} is not called.
       */
      public abstract void beginSampling(int capacity, long durationMillis);
  
      /**
       * Stop sampling and return the results
       * @param count The number of the samples requested to retrieve from the sampler
       * @return a list of samples, the size is the minimum of the total samples and {@param count}.
       */
      public abstract List<Sample<T>> finishSampling(int count);
  
      public abstract String toString(T value);
  
      /**
       * Represents the ranked items collected during a sample period
       */
      public static class Sample<S> implements Serializable
      {
          private static final long serialVersionUID = 0;  // for simulator support
          public final S value;
          public final long count;
          public final long error;
  
          public Sample(S value, long count, long error)
          {
              this.value = value;
              this.count = count;
              this.error = error;
          }
  
          @Override
          public String toString()
          {
              return "Sample [value=" + value + ", count=" + count + ", error=" + error + "]";
          }
      }
  
      public static void shutdownNowAndWait(long time, TimeUnit units) throws InterruptedException, TimeoutException
      {
          ExecutorUtils.shutdownNowAndWait(time, units, samplerExecutor);
      }
  }
  