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From Xiangrui Meng <men...@gmail.com>
Subject Switch RDD-based MLlib APIs to maintenance mode in Spark 2.0
Date Tue, 05 Apr 2016 18:01:16 GMT
Hi all,

More than a year ago, in Spark 1.2 we introduced the ML pipeline API built
on top of Spark SQL’s DataFrames. Since then the new DataFrame-based API
has been developed under the spark.ml package, while the old RDD-based API
has been developed in parallel under the spark.mllib package. While it was
easier to implement and experiment with new APIs under a new package, it
became harder and harder to maintain as both packages grew bigger and
bigger. And new users are often confused by having two sets of APIs with
overlapped functions.

We started to recommend the DataFrame-based API over the RDD-based API in
Spark 1.5 for its versatility and flexibility, and we saw the development
and the usage gradually shifting to the DataFrame-based API. Just counting
the lines of Scala code, from 1.5 to the current master we added ~10000
lines to the DataFrame-based API while ~700 to the RDD-based API. So, to
gather more resources on the development of the DataFrame-based API and to
help users migrate over sooner, I want to propose switching RDD-based MLlib
APIs to maintenance mode in Spark 2.0. What does it mean exactly?

* We do not accept new features in the RDD-based spark.mllib package,
unless they block implementing new features in the DataFrame-based spark.ml
package.
* We still accept bug fixes in the RDD-based API.
* We will add more features to the DataFrame-based API in the 2.x series to
reach feature parity with the RDD-based API.
* Once we reach feature parity (possibly in Spark 2.2), we will deprecate
the RDD-based API.
* We will remove the RDD-based API from the main Spark repo in Spark 3.0.

Though the RDD-based API is already in de facto maintenance mode, this
announcement will make it clear and hence important to both MLlib
developers and users. So we’d greatly appreciate your feedback!

(As a side note, people sometimes use “Spark ML” to refer to the
DataFrame-based API or even the entire MLlib component. This also causes
confusion. To be clear, “Spark ML” is not an official name and there are no
plans to rename MLlib to “Spark ML” at this time.)

Best,
Xiangrui

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