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Date: Mon, 29 Sep 2008 16:44:44 -0700 (PDT)
From: "Doug Cutting (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-4049) Cross-system causal tracing within
 Hadoop
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    [ https://issues.apache.org/jira/browse/HADOOP-4049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12635600#action_12635600 ] 

Doug Cutting commented on HADOOP-4049:
--------------------------------------

+1 This looks good to me.  Have you run any RPC-intensive benchmarks?

> Cross-system causal tracing within Hadoop
> -----------------------------------------
>
>                 Key: HADOOP-4049
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4049
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs, ipc, mapred
>    Affects Versions: 0.18.0, 0.18.1
>            Reporter: George Porter
>         Attachments: HADOOP-4049.2-ipc.patch, HADOOP-4049.3-ipc.patch, HADOOP-4049.4-rpc.patch, HADOOP-4049.6-rpc.patch, HADOOP-4049.7-rpc.patch, HADOOP-4049.patch, multiblockread.png, multiblockwrite.png
>
>
> Much of Hadoop's behavior is client-driven, with clients responsible for contacting individual datanodes to read and write data, as well as dividing up work for map and reduce tasks.  In a large deployment with many concurrent users, identifying the effects of individual clients on the infrastructure is a challenge.  The use of data pipelining in HDFS and Map/Reduce make it hard to follow the effects of a given client request through the system.
> This proposal is to instrument the HDFS, IPC, and Map/Reduce layers of Hadoop with X-Trace.  X-Trace is an open-source framework for capturing causality of events in a distributed system.  It can correlate operations making up a single user request, even if those operations span multiple machines.  As an example, you could use X-Trace to follow an HDFS write operation as it is pipelined through intermediate nodes.  Additionally, you could trace a single Map/Reduce job and see how it is decomposed into lower-layer HDFS operations.
> Matei Zaharia and Andy Konwinski initially integrated X-Trace with a local copy of the 0.14 release, and I've brought that code up to release 0.17.  Performing the integration involves modifying the IPC protocol, inter-datanode protocol, and some data structures in the map/reduce layer to include 20-byte long tracing metadata.  With release 0.18, the generated traces could be collected with Chukwa.
> I've attached some example traces of HDFS and IPC layers from the 0.17 patch to this JIRA issue.
> More information about X-Trace is available from http://www.x-trace.net/ as well as in a paper that appeared at NSDI 2007, available online at http://www.usenix.org/events/nsdi07/tech/fonseca.html

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