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https://issues.apache.org/jira/browse/HADOOP-13341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15476796#comment-15476796
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ASF GitHub Bot commented on HADOOP-13341:
-----------------------------------------
Github user aw-was-here commented on a diff in the pull request:
https://github.com/apache/hadoop/pull/126#discussion_r78162457
--- Diff:
hadoop-common-project/hadoop-common/src/site/markdown/UnixShellGuide.md ---
@@ -24,14 +24,26 @@ Apache Hadoop has many environment variables that
control various aspects of the
### `HADOOP_CLIENT_OPTS`
-This environment variable is used for almost all end-user operations. It
can be used to set any Java options as well as any Apache Hadoop options via a
system property definition. For example:
+This environment variable is used for all end-user, non-daemon operations.
It can be used to set any Java options as well as any Apache Hadoop options
via a system property definition. For example:
```bash
HADOOP_CLIENT_OPTS="-Xmx1g -Dhadoop.socks.server=localhost:4000" hadoop fs
-ls /tmp
```
will increase the memory and send this command via a SOCKS proxy server.
+### `(command)_(subcommand)_OPTS`
+
+It is also possible to set options on a per subcommand basis. This allows
for one to create special options for particular cases. The first part of the
pattern is the command being used, but all uppercase. The second part of the
command is the subcommand being used. Then finally followed by the string
`_OPT`.
+
+For example, to configure `mapred distcp` to use a 2GB heap, one would use:
+
+```bash
+MAPRED_DISTCP_OPTS="-Xmx2g"
+```
+
+These options will appear *after* `HADOOP_CLIENT_OPTS` during execution
and will generally take precedence.
--- End diff --
If there is an Xmx in HADOOP_CLIENT_OPTS and an Xmx in MAPRED_DISTCP_OPTS,
then the mapred distcp final HADOOP_OPTS will definitely have two Xmx flags.
After HADOOP-13365, we'll be in a position to potentially de-dupe user provided
settings like we do for other things. But until de-dupe, you're correct that
it's a JVM decision. In the past, that decision has been last one wins and I
doubt Oracle could change it if they wanted to at this point without major
ramifications.
> Deprecate HADOOP_SERVERNAME_OPTS; replace with (command)_(subcommand)_OPTS
> --------------------------------------------------------------------------
>
> Key: HADOOP-13341
> URL: https://issues.apache.org/jira/browse/HADOOP-13341
> Project: Hadoop Common
> Issue Type: Improvement
> Components: scripts
> Affects Versions: 3.0.0-alpha1
> Reporter: Allen Wittenauer
> Assignee: Allen Wittenauer
> Attachments: HADOOP-13341.00.patch
>
>
> Big features like YARN-2928 demonstrate that even senior level Hadoop
> developers forget that daemons need a custom _OPTS env var. We can replace
> all of the custom vars with generic handling just like we do for the username
> check.
> For example, with generic handling in place:
> || Old Var || New Var ||
> | HADOOP_NAMENODE_OPTS | HDFS_NAMENODE_OPTS |
> | YARN_RESOURCEMANAGER_OPTS | YARN_RESOURCEMANAGER_OPTS |
> | n/a | YARN_TIMELINEREADER_OPTS |
> | n/a | HADOOP_DISTCP_OPTS |
> | n/a | MAPRED_DISTCP_OPTS |
> | HADOOP_DN_SECURE_EXTRA_OPTS | HDFS_DATANODE_SECURE_EXTRA_OPTS |
> | HADOOP_NFS3_SECURE_EXTRA_OPTS | HDFS_NFS3_SECURE_EXTRA_OPTS |
> | HADOOP_JOB_HISTORYSERVER_OPTS | MAPRED_HISTORYSERVER_OPTS |
> This makes it:
> a) consistent across the entire project
> b) consistent for every subcommand
> c) eliminates almost all of the custom appending in the case statements
> It's worth pointing out that subcommands like distcp that sometimes need a
> higher than normal client-side heapsize or custom options are a huge win.
> Combined with .hadooprc and/or dynamic subcommands, it means users can easily
> do customizations based upon their needs without a lot of weirdo shell
> aliasing or one line shell scripts off to the side.
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