Hi Matei, Thanks for your reply.
The Writable classes have never been serializable and this is why it is weird. I did try as you suggested to map the Writables to integers and strings. It didn’t pass, either. Similar exceptions were thrown except that the messages became IntWritable, Text are not serializable. The reason is in the implicits defined in the SparkContext object that convert those values into their corresponding Writable classes before saving the data in sequence file. My original code was actual some test cases to try out SequenceFile related APIs. The tests all passed when the spark version was specified as 1.0.2. But this one failed after I changed the spark version to 1.1.0 the new release, nothing else changed. In addition, it failed when I called rdd2.collect(), take(1), and first(). But it worked fine when calling rdd2.count(). As you can see, count() does not need to serialize and ship data while the other three methods do. Do you recall any difference between spark 1.0 and 1.1 that might cause this problem? Thanks, Du From: Matei Zaharia <matei.zaha...@gmail.com<mailto:matei.zaha...@gmail.com>> Date: Friday, September 12, 2014 at 9:10 PM To: Du Li <l...@yahoo-inc.com.invalid<mailto:l...@yahoo-inc.com.invalid>>, "user@spark.apache.org<mailto:user@spark.apache.org>" <user@spark.apache.org<mailto:user@spark.apache.org>>, "d...@spark.apache.org<mailto:d...@spark.apache.org>" <d...@spark.apache.org<mailto:d...@spark.apache.org>> Subject: Re: NullWritable not serializable Hi Du, I don't think NullWritable has ever been serializable, so you must be doing something differently from your previous program. In this case though, just use a map() to turn your Writables to serializable types (e.g. null and String). Matie On September 12, 2014 at 8:48:36 PM, Du Li (l...@yahoo-inc.com.invalid<mailto:l...@yahoo-inc.com.invalid>) wrote: Hi, I was trying the following on spark-shell (built with apache master and hadoop 2.4.0). Both calling rdd2.collect and calling rdd3.collect threw java.io.NotSerializableException: org.apache.hadoop.io.NullWritable. I got the same problem in similar code of my app which uses the newly released Spark 1.1.0 under hadoop 2.4.0. Previously it worked fine with spark 1.0.2 under either hadoop 2.40 and 0.23.10. Anybody knows what caused the problem? Thanks, Du ---- import org.apache.hadoop.io.{NullWritable, Text} val rdd = sc.textFile("README.md") val res = rdd.map(x => (NullWritable.get(), new Text(x))) res.saveAsSequenceFile("./test_data") val rdd2 = sc.sequenceFile("./test_data", classOf[NullWritable], classOf[Text]) rdd2.collect val rdd3 = sc.sequenceFile[NullWritable,Text]("./test_data") rdd3.collect
