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HBase Metrics API descriptions
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/*
 * 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.hadoop.hbase.metrics;

import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.yetus.audience.InterfaceAudience;
import org.apache.yetus.audience.InterfaceStability;

/**
 * A metric which measure the rate at which some operation is invoked.
 */
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
@InterfaceStability.Evolving
public interface Meter extends Metric {

  /**
   * Records one occurrence.
   */
  void mark();

  /**
   * Records {@code events} occurrences.
   * @param events Number of occurrences to record.
   */
  void mark(long events);

  /**
   * Returns the number of events.
   * @return the number of events.
   */
  long getCount();

  /**
   * Returns the mean rate at which events have occurred since the meter was created.
   * @return the mean rate at which events have occurred since the meter was created
   */
  double getMeanRate();

  /**
   * Returns the one-minute exponentially-weighted moving average rate at which events have occurred
   * since the meter was created.
   * 
   * This rate has the same exponential decay factor as the one-minute load average in the {@code
   * top} Unix command.
   * @return the one-minute exponentially-weighted moving average rate at which events have occurred
   *         since the meter was created
   */
  double getOneMinuteRate();

  /**
   * Returns the five-minute exponentially-weighted moving average rate at which events have
   * occurred since the meter was created.
   * 

   * This rate has the same exponential decay factor as the five-minute load average in the {@code
   * top} Unix command.
   * @return the five-minute exponentially-weighted moving average rate at which events have
   *         occurred since the meter was created
   */
  double getFiveMinuteRate();

  /**
   * Returns the fifteen-minute exponentially-weighted moving average rate at which events have
   * occurred since the meter was created.
   * 
   * This rate has the same exponential decay factor as the fifteen-minute load average in the
   * {@code top} Unix command.
   * @return the fifteen-minute exponentially-weighted moving average rate at which events have
   *         occurred since the meter was created
   */
  double getFifteenMinuteRate();
}