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From "Topher ZiCornell (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-5708) Configuration should provide a way to write only properties that have been set
Date Mon, 20 Apr 2009 20:18:47 GMT
Configuration should provide a way to write only properties that have been set
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                 Key: HADOOP-5708
                 URL: https://issues.apache.org/jira/browse/HADOOP-5708
             Project: Hadoop Core
          Issue Type: Improvement
          Components: conf
    Affects Versions: 0.19.1
            Reporter: Topher ZiCornell
            Priority: Minor


The Configuration.write and .writeXml methods always output all properties, whether they came
from a default source, a loaded resource file, or an "overlay" set call.  There should be
a way to write only the properties that were set, leaving out the properties that came from
a default source.

Why?  Suppose I build a configuration on a machine that is not associated with a grid, write
it out to XML, then try to load it on a grid gateway.  The configuration would contain all
of the defaults picked up from my non-grid machine, and would completely overwrite all the
defaults on that grid.

I propose to add methods to write out only the overlay values in Object and XML formats.

I see two options for implementing this:
1) Either completely new methods could be crafted (writeOverlay(DataOutput) and writeOverlayXml(OutputStream),
or 
2) The existing write() and writeXml() methods could be adjusted to take an additional parameter
indicating whether the full properties or overlay properties should be written.  (Of course,
the existing write() and writeXml() methods would remain, defaulting to the current behavior.)

Option 1 has less impact to existing code.  Option 2 is a cleaner implementation with less
code-duplication involved.  I would much prefer to do option 2.

Oh, and in case it's not clear, I'm offering to make this change and submit it.

Thoughts?

.  Topher

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