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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5743) Configuration: Hierachical; documented; null-safe; thread-safe
Date Fri, 24 Apr 2009 21:39:30 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12702568#action_12702568

Doug Cutting commented on HADOOP-5743:

I don't know all of the places where Configuration is used as a Writable, but my hunch is
that it's okay to change its format.  Where it's passed in an RPC, an incompatible change
is okay, since we don't permit cross-version RPC.  Configurations are written to disk on the
job tracker, but I don't think we guarantee that the job queue survives upgrades.

It might be nice is if it included a version number in the serialized form.  The new version
could be -1, so that old code reading the new format would see this as the size and fail.
 But new code reading the old could do something back-compatible when the version is positive.

There are still lots of whitespace-only changes in your patch that inject noise and make me
stop reading it.

I'm also not (yet) highly incented to spend a lot of time reviewing this, since it's not entirely
clear to me that this is fixing problems that folks are actually encountering.  Radically
changing something low-level like this has a very good chance of breaking lots of systems,
which will take a lot of time to debug and fix, and should thus not be entered into lightly.

That said, if you feel strongly, I encourage you to develop this to the point where it passes
unit tests and can be automatically tested by Hudson.  Also, please read your patch files
before you submit them to see that they only include changes that are critical to your mission.
 They should not include discussions of the changes annotated with your name.  Jira is for
discussion of patches.


> Configuration: Hierachical; documented; null-safe; thread-safe
> --------------------------------------------------------------
>                 Key: HADOOP-5743
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5743
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: conf
>            Reporter: Shevek
>         Attachments: 01_configuration.patch, 02_configuration.patch
> Patch to configuration to:
> * Update documentation to match code
> * Make configurations hierarchical
> * Remove global REGISTRY of configurations
> * Adding global default does not reload child configurations
> * (Eventually) make properly thread-safe
> * Allow well-behaved overriding with nulls
> * Allow future satisfaction of ticket 5708 (with which I agree, but Doug does not).

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