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From "Doug Cutting (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7939) Improve Hadoop subcomponent integration in Hadoop 0.23
Date Thu, 19 Jan 2012 19:44:41 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13189335#comment-13189335
] 

Doug Cutting commented on HADOOP-7939:
--------------------------------------

> we are currently debating adding features here which Apache Hadoop will never use

Many if not most of Hadoop's features are primarily used by downstream projects.  BigTop will
use these features, as would any other downstream packager.  So lack of use of a feature within
Hadoop itself does not seem like a reason to reject a feature.

> and then we are assuming the burden of maintenance

Do you think downstream packagers like BigTop will disappear?  They are trying to maintain
this stuff, right here, now.  This is not a drive-by contribution.

> it would be useful for folks in Apache Bigtop project to share why they feel they cannot
collaborate with Apache Hadoop

They are trying to collaborate with Apache Hadoop right here.  They seem to reasonably believe
that downstream packaging makes more sense, for the reasons I outlined above.  Consider HBase,
Pig & Hive, which each might like to ship a single release that's compatible with multiple
releases of Hadoop, e.g, 0.20.205 and 0.23, which have different layouts.  Must each of these
projects duplicate the logic required to handle these different layouts?  Why would you inhibit
folks from trying to consolidate that logic downstream?

                
> Improve Hadoop subcomponent integration in Hadoop 0.23
> ------------------------------------------------------
>
>                 Key: HADOOP-7939
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7939
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: build, conf, documentation, scripts
>    Affects Versions: 0.23.0
>            Reporter: Roman Shaposhnik
>            Assignee: Roman Shaposhnik
>             Fix For: 0.23.1
>
>         Attachments: HADOOP-7939.patch.txt, hadoop-layout.sh
>
>
> h1. Introduction
> For the rest of this proposal it is assumed that the current set
> of Hadoop subcomponents is:
>  * hadoop-common
>  * hadoop-hdfs
>  * hadoop-yarn
>  * hadoop-mapreduce
> It must be noted that this is an open ended list, though. For example,
> implementations of additional frameworks on top of yarn (e.g. MPI) would
> also be considered a subcomponent.
> h1. Problem statement
> Currently there's an unfortunate coupling and hard-coding present at the
> level of launcher scripts, configuration scripts and Java implementation
> code that prevents us from treating all subcomponents of Hadoop independently
> of each other. In a lot of places it is assumed that bits and pieces
> from individual subcomponents *must* be located at predefined places
> and they can not be dynamically registered/discovered during the runtime.
> This prevents a truly flexible deployment of Hadoop 0.23. 
> h1. Proposal
> NOTE: this is NOT a proposal for redefining the layout from HADOOP-6255. 
> The goal here is to keep as much of that layout in place as possible,
> while permitting different deployment layouts.
> The aim of this proposal is to introduce the needed level of indirection and
> flexibility in order to accommodate the current assumed layout of Hadoop tarball
> deployments and all the other styles of deployments as well. To this end the
> following set of environment variables needs to be uniformly used in all of
> the subcomponent's launcher scripts, configuration scripts and Java code
> (<SC> stands for a literal name of a subcomponent). These variables are
> expected to be defined by <SC>-env.sh scripts and sourcing those files is
> expected to have the desired effect of setting the environment up correctly.
>   # HADOOP_<SC>_HOME
>    ## root of the subtree in a filesystem where a subcomponent is expected to be installed

>    ## default value: $0/..
>   # HADOOP_<SC>_JARS 
>    ## a subdirectory with all of the jar files comprising subcomponent's implementation

>    ## default value: $(HADOOP_<SC>_HOME)/share/hadoop/$(<SC>)
>   # HADOOP_<SC>_EXT_JARS
>    ## a subdirectory with all of the jar files needed for extended functionality of the
subcomponent (nonessential for correct work of the basic functionality)
>    ## default value: $(HADOOP_<SC>_HOME)/share/hadoop/$(<SC>)/ext
>   # HADOOP_<SC>_NATIVE_LIBS
>    ## a subdirectory with all the native libraries that component requires
>    ## default value: $(HADOOP_<SC>_HOME)/share/hadoop/$(<SC>)/native
>   # HADOOP_<SC>_BIN
>    ## a subdirectory with all of the launcher scripts specific to the client side of
the component
>    ## default value: $(HADOOP_<SC>_HOME)/bin
>   # HADOOP_<SC>_SBIN
>    ## a subdirectory with all of the launcher scripts specific to the server/system side
of the component
>    ## default value: $(HADOOP_<SC>_HOME)/sbin
>   # HADOOP_<SC>_LIBEXEC
>    ## a subdirectory with all of the launcher scripts that are internal to the implementation
and should *not* be invoked directly
>    ## default value: $(HADOOP_<SC>_HOME)/libexec
>   # HADOOP_<SC>_CONF
>    ## a subdirectory containing configuration files for a subcomponent
>    ## default value: $(HADOOP_<SC>_HOME)/conf
>   # HADOOP_<SC>_DATA
>    ## a subtree in the local filesystem for storing component's persistent state
>    ## default value: $(HADOOP_<SC>_HOME)/data
>   # HADOOP_<SC>_LOG
>    ## a subdirectory for subcomponents's log files to be stored
>    ## default value: $(HADOOP_<SC>_HOME)/log
>   # HADOOP_<SC>_RUN
>    ## a subdirectory with runtime system specific information
>    ## default value: $(HADOOP_<SC>_HOME)/run
>   # HADOOP_<SC>_TMP
>    ## a subdirectory with temprorary files
>    ## default value: $(HADOOP_<SC>_HOME)/tmp

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