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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5090) Expose optionally detailed metrics about network queue lengths
Date Thu, 02 Mar 2017 15:20:45 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15892404#comment-15892404
] 

ASF GitHub Bot commented on FLINK-5090:
---------------------------------------

Github user zentol commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3348#discussion_r103948091
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/consumer/InputGateMetrics.java
---
    @@ -0,0 +1,168 @@
    +/*
    + * 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.flink.runtime.io.network.partition.consumer;
    +
    +import org.apache.flink.metrics.Gauge;
    +import org.apache.flink.metrics.MetricGroup;
    +
    +import static org.apache.flink.util.Preconditions.checkNotNull;
    +
    +public class InputGateMetrics {
    +
    +	private final SingleInputGate inputGate;
    +
    +	private long lastTotal = -1;
    +
    +	private int lastMin = -1;
    +
    +	private int lastMax = -1;
    +
    +	private float lastAvg = -1.0f;
    +
    +	// ------------------------------------------------------------------------
    +
    +	private InputGateMetrics(SingleInputGate inputGate) {
    +		this.inputGate = checkNotNull(inputGate);
    +	}
    +
    +	// ------------------------------------------------------------------------
    +
    +	// these methods are package private to make access from the nested classes faster 
    +
    +	long refreshAndGetTotal() {
    +		long total;
    +		if ((total = lastTotal) == -1) {
    +			refresh();
    --- End diff --
    
    I'm not sure whether this pattern is really worth it.
    
    The stated goal is that the values returned by the gauges all originate from the same
point in time. However this only holds if all gauges are accessed in sequence. The moment
that a metric is accessed multiple times (like a reporter that writes to multiple systems
and first loops over metrics and then over reporters), or in a random pattern (JMX) this breaks
down. In this case the end result isn't just out-of-sync but potentially outdated metrics.
    
    Say with JMX a user accesses one of the gauges a single time and then waits for, let's
say 10 minutes. If he now access another metric the result will be that of 10 minutes ago.
If he accesses the value again he will experience a(n abnormally large) jump in time, which
is inconsistent with all other metrics that always provide the most up-to-date value.


> Expose optionally detailed metrics about network queue lengths
> --------------------------------------------------------------
>
>                 Key: FLINK-5090
>                 URL: https://issues.apache.org/jira/browse/FLINK-5090
>             Project: Flink
>          Issue Type: New Feature
>          Components: Metrics, Network
>    Affects Versions: 1.1.3
>            Reporter: Stephan Ewen
>            Assignee: Stephan Ewen
>
> For debugging purposes, it is important to have access to more detailed metrics about
the length of network input and output queues.



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