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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