[GitHub] [spark] zhengruifeng commented on pull request #37918: [SPARK-40476][ML][SQL] Reduce the shuffle size of ALS

[GitBox <gi...@apache.org>]

zhengruifeng commented on PR #37918:
URL: https://github.com/apache/spark/pull/37918#issuecomment-1249957261

   take the [`ALSExample`](https://github.com/apache/spark/blob/e1ea806b3075d279b5f08a29fe4c1ad6d3c4191a/examples/src/main/scala/org/apache/spark/examples/ml/ALSExample.scala) for example:
   
   ```
   import org.apache.spark.ml.recommendation._
   
   case class Rating(userId: Int, movieId: Int, rating: Float, timestamp: Long)
   
   def parseRating(str: String): Rating = {
       val fields = str.split("::")
       assert(fields.size == 4)
       Rating(fields(0).toInt, fields(1).toInt, fields(2).toFloat, fields(3).toLong)
   }
   
   val ratings = spark.read.textFile("data/mllib/als/sample_movielens_ratings.txt").map(parseRating).toDF()
   
   val als = new ALS().setMaxIter(1).setRegParam(0.01).setUserCol("userId").setItemCol("movieId").setRatingCol("rating")
   
   val model = als.fit(ratings)
   
   model.recommendForAllItems(10).collect()
   ```
   
   before:
   <img width="1704" alt="image" src="https://user-images.githubusercontent.com/7322292/190832964-3f31bcd4-6bfb-445a-a339-b415f82719e3.png">
   
   
   
   after:
   <img width="1708" alt="image" src="https://user-images.githubusercontent.com/7322292/190832980-d0ccc2d3-f4d9-4801-9046-9d56f2fbab3c.png">
   
   
   the shuffle size in this case was reduced from `298.4 KiB` to `130.3 KiB`


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