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From "Edward Capriolo (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1096) Hive Variables
Date Fri, 19 Feb 2010 15:46:28 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12835785#action_12835785
] 

Edward Capriolo commented on HIVE-1096:
---------------------------------------

{quote}
True, but I think we should try to improve the situation. As a start we can add code to throw
an error if hive-default.xml or hive-site.xml sets a hive.* configuration property that is
not defined in HiveConf. This would protect the hive.* namespace and at the same time make
it easy to track down cases where folks misspell a hive.* property name.
{quote}

I only see one problem with this. HiveConf has an enumeration of valid properties. I do not
think Hadoop Conf shares that trait. So if someone were to say: 
{noformat}
set hadoop.wrong.variable.name
{noformat}
Would we have a simple way of knowing if that variable was variable is valid. Anyway that
is out of scope a bit.

{quote}
${namespace:variable_name}.
{quote}
I like this. How about?
{noformat}
${hiveconf:variable_name}.
${env:variable_name}.
${property:variable_name}.
{noformat}

This way we do not need the "-hivevar x=y" switch." I say this because we already have three
mechanism to pass data into Java/hive adding a forth is a little confusing.  

The only problem with introducing this is now we have a new question. How do we extend SET
to read/write these?

> Hive Variables
> --------------
>
>                 Key: HIVE-1096
>                 URL: https://issues.apache.org/jira/browse/HIVE-1096
>             Project: Hadoop Hive
>          Issue Type: New Feature
>            Reporter: Edward Capriolo
>            Assignee: Edward Capriolo
>         Attachments: 1096-9.diff, hive-1096-2.diff, hive-1096-7.diff, hive-1096-8.diff,
hive-1096.diff
>
>
> From mailing list:
> --Amazon Elastic MapReduce version of Hive seems to have a nice feature called "Variables."
Basically you can define a variable via command-line while invoking hive with -d DT=2009-12-09
and then refer to the variable via ${DT} within the hive queries. This could be extremely
useful. I can't seem to find this feature even on trunk. Is this feature currently anywhere
in the roadmap?--
> This could be implemented in many places.
> A simple place to put this is 
> in Driver.compile or Driver.run we can do string substitutions at that level, and further
downstream need not be effected. 
> There could be some benefits to doing this further downstream, parser,plan. but based
on the simple needs we may not need to overthink this.
> I will get started on implementing in compile unless someone wants to discuss this more.

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