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https://issues.apache.org/jira/browse/HADOOP-4049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12634963#action_12634963
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Doug Cutting commented on HADOOP-4049:
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We should be able to do this without replicating the logic of
ObjectWritable#writeObject and #readObject. Why can't you just invoke
super.writeObject() and super.readObject() from the implementations? If your
ObjectWritable subclass was called RPCResponse, and RPC's always returned
instances of this, regardless of whether instrumentation is enabled, and it has
a pathState field, but the pathState might be null, would that make things
simpler?
> 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.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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