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https://issues.apache.org/jira/browse/HADOOP-7939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13176779#comment-13176779
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Roman Shaposhnik commented on HADOOP-7939:
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@Eric
I believe your constant appeal to "complexity" and "un-manageability" of the
proposed solution is not only the red herring here, but also serves as a
detraction from the current sad state of things. Hadoop scripts already have as
many (if not more!) env. variables dedicated to locating various things.
As one of its goals, this proposal aims at rationalizing the naming convention
and clearly documenting what every single one of them does.
Finally, when you say that there could be a simpler solution, I'm curious, but
not hopeful. If you look at an example of any modern Unix packaging/deployment
system you'd see that they hall pretty much the same set of knobs to tweak
(e.g. read the section of the following RPM
doc that says *Use these macros wherever possible to avoid hard-coded paths and
settings*:
http://docs.fedoraproject.org/en-US/Fedora_Draft_Documentation/0.1/html/RPM_Guide/ch09s07.html
). Even autotools have pretty much the same set of knobs. I think there's a
reason
UNIX community hasn't come up with a simpler implementation in all these years.
> 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
>
>
> 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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