Github user pwendell commented on a diff in the pull request:
https://github.com/apache/spark/pull/42#discussion_r10186680
--- Diff: core/src/main/scala/org/apache/spark/ui/UISparkListener.scala ---
@@ -0,0 +1,210 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ui
+
+import scala.collection.mutable
+import scala.collection.mutable.ArrayBuffer
+
+import org.json4s.jackson.JsonMethods._
+
+import org.apache.spark.scheduler._
+import org.apache.spark.storage._
+import org.apache.spark.util.FileLogger
+import org.apache.spark.util.JsonProtocol
+
+private[ui] trait UISparkListener extends SparkListener
+
+/**
+ * A SparkListener that serves as an entry point for all events posted to
the UI.
+ *
+ * GatewayUISparkListener achieves two functions:
+ *
+ * (1) If the UI is live, GatewayUISparkListener posts each event to all
attached listeners
+ * then logs it as JSON. This centralizes event logging and avoids
having all attached
+ * listeners log the events on their own. By default,
GatewayUISparkListener logs one
+ * file per job, though this needs not be the case.
+ *
+ * (2) If the UI is rendered from disk, GatewayUISparkListener replays
each event deserialized
+ * from the event logs to all attached listeners.
+ */
+private[ui] class GatewayUISparkListener(parent: SparkUI, live: Boolean)
extends SparkListener {
--- End diff --
I think as a starting point it would be better to just log at application
boundaries rather than job boundaries. I.e. just have a single log for the
entire spark application. This class makes the assumption that jobs are
(mostly) sequential, but in fact stages and tasks from different jobs can be
interleaved. So rolling the log based on onJobStart/onJobEnd is not correct.
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