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https://issues.apache.org/jira/browse/SPARK-15573?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15836604#comment-15836604
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Asher Krim commented on SPARK-15573:
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Thanks for your comment [~jkbradley]
What I mean by "coupling" is that relying on the spark version means that
there's a time element to a PR which, to me at least, feels foreign. Imagine a
commiter who uses spark 2.2 as the version for a fix, but the PR gets delayed
to 2.3. Now a code change is needed, but there might not be any test or compile
errors to make that obvious.
Regarding backporting, what I have in mind is specifically making bugfixes
back-portable to a future 1.6.x release. For example, there are bugs in the
word2vec+LDA model save logic. Relying on the spark version makes it clunky to
backport the fix (the code would have to be different to account for different
spark versions).
I agree that relying on columns/content can be problematic for the reason you
mentioned.
Relying on an internal version flag like in MLlib seems like the lesser evil.
I'm wondering, is there a particular reason that it was abandoned in ML?
> Backwards-compatible persistence for spark.ml
> ---------------------------------------------
>
> Key: SPARK-15573
> URL: https://issues.apache.org/jira/browse/SPARK-15573
> Project: Spark
> Issue Type: Improvement
> Components: ML
> Reporter: Joseph K. Bradley
>
> This JIRA is for imposing backwards-compatible persistence for the
> DataFrames-based API for MLlib. I.e., we want to be able to load models
> saved in previous versions of Spark. We will not require loading models
> saved in later versions of Spark.
> This requires:
> * Putting unit tests in place to check loading models from previous versions
> * Notifying all committers active on MLlib to be aware of this requirement in
> the future
> The unit tests could be written as in spark.mllib, where we essentially
> copied and pasted the save() code every time it changed. This happens
> rarely, so it should be acceptable, though other designs are fine.
> Subtasks of this JIRA should cover checking and adding tests for existing
> cases, such as KMeansModel (whose format changed between 1.6 and 2.0).
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