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From AlexG <swift...@gmail.com>
Subject spark hangs at broadcasting during a filter
Date Wed, 05 Aug 2015 18:54:50 GMT
I'm trying to load a 1 Tb file whose lines i,j,v represent the values of a
matrix given as A_{ij} = v so I can convert it to a Parquet file. Only some
of the rows of A are relevant, so the following code first loads the
triplets are text, splits them into Tuple3[Int, Int, Double], drops triplets
whose rows should be skipped, then forms a Tuple2[Int, List[Tuple2[Int,
Double]]] for each row (if I'm judging datatypes correctly).

val valsrows = sc.textFile(valsinpath).map(_.split(",")).
                          map(x => (x(1).toInt, (x(0).toInt,
x(2).toDouble))).
                          filter(x => !droprows.contains(x._1)).
                          groupByKey.
                          map(x => (x._1, x._2.toSeq.sortBy(_._1)))

Spark hangs during a broadcast that occurs during the filter step (according
to the Spark UI). The last two lines in the log before it pauses are:

5/08/05 18:50:10 INFO storage.BlockManagerInfo: Added broadcast_3_piece0 in
memory on 172.31.49.149:37643 (size: 4.6 KB, free: 113.8 GB)
15/08/05 18:50:10 INFO storage.BlockManagerInfo: Added broadcast_3_piece0 in
memory on 172.31.49.159:41846 (size: 4.6 KB, free: 113.8 GB)

I've left Spark running for up to 17 minutes one time, and it never
continues past this point. I'm using a cluster of 30 r3.8xlarge EC2
instances (244Gb, 32 cores) with spark in standalone mode with 220G executor
and driver memory, and using the kyroserializer.

Any ideas on what could be causing this hang?



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