Github user JoshRosen commented on a diff in the pull request: https://github.com/apache/spark/pull/3009#discussion_r20759212 --- Diff: core/src/main/scala/org/apache/spark/util/JsonProtocol.scala --- @@ -31,6 +31,21 @@ import org.apache.spark.scheduler._ import org.apache.spark.storage._ import org.apache.spark._ +/** + * Serializes SparkListener events to/from JSON. This protocol provides strong backwards- + * and forwards-compatibility guarantees: any version of Spark should be able to read JSON output + * written by any other version, including newer versions. + * + * JsonProtocolSuite contains backwards-compatibility tests which check that the current version of + * JsonProtocol is able to read output written by earlier versions. We do not currently have tests + * for reading newer JSON output with older Spark versions. + * + * To ensure that we provide these guarantees, follow these rules when modifying these methods: + * + * - Never delete any JSON fields. + * - Any new JSON fields should be optional; use `Utils.jsonOption` when reading these fields + * in `*FromJson` methods. + */ --- End diff -- I agree; I've filed https://issues.apache.org/jira/browse/SPARK-4555 for this.
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