title: How to read a compressed Spark eventLog?
body: <p>When I try to read a Spark 2.4.4 eventLog compressed with lz4, I obtain an empty DataFrame:</p>
  
  <pre><code>cd /opt/spark-2.4.4-bin-hadoop2.7
  bin/spark-shell --master=local --conf spark.eventLog.enabled=true --conf spark.eventLog.compress=true --conf spark.io.compression.codec=lz4 --driver-memory 4G --driver-library-path=/opt/hadoop-2.7.1/lib/native/
  
  // Trying to read an event log from a previous session
  spark.read.option("compression", "lz4").json(s"file:///tmp/spark-events/local-1589202668377.lz4")
  
  // res0: org.apache.spark.sql.DataFrame = []                                       
  </code></pre>
  
  <p>However it works fine when I read an uncompressed eventLog:</p>
  
  <pre><code>bin/spark-shell --master=local --conf spark.eventLog.enabled=true --conf spark.eventLog.compress=false
  spark.read.json(s"file:///tmp/spark-events/${sc.applicationId}.inprogress").printSchema
  
  //root
  // |-- App ID: string (nullable = true)
  // |-- App Name: string (nullable = true)
  // |-- Block Manager ID: struct (nullable = true)
  // |    |-- Executor ID: string (nullable = true)
  </code></pre>
  
  <p>I also tried to read an eventLog compressed with snappy, same result.</p>