001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.metrics2.annotation;
020
021import java.lang.annotation.*;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025
026/**
027 * Annotation interface for a single metric
028 */
029@InterfaceAudience.Public
030@InterfaceStability.Evolving
031@Documented
032@Target({ElementType.FIELD, ElementType.METHOD})
033@Retention(RetentionPolicy.RUNTIME)
034public @interface Metric {
035
036  public enum Type {
037    DEFAULT, COUNTER, GAUGE, TAG
038  }
039
040  /**
041   * Shorthand for optional name and description
042   * @return {description} or {name, description}
043   */
044  String[] value() default {};
045
046  /**
047   * @return optional description of the metric
048   */
049  String about() default "";
050
051  /**
052   * @return optional sample name for MutableStat/Rate/Rates
053   */
054  String sampleName() default "Ops";
055
056  /**
057   * @return optional value name for MutableStat/Rate/Rates
058   */
059  String valueName() default "Time";
060
061  /**
062   * @return true to create a metric snapshot even if unchanged.
063   */
064  boolean always() default false;
065
066  /**
067   * @return optional type (counter|gauge) of the metric
068   */
069  Type type() default Type.DEFAULT;
070}