[SPARK-10955] [STREAMING] Add a warning if dynamic allocation for Streaming applications

Dynamic allocation can be painful for streaming apps and can lose data. Log a warning for streaming applications if dynamic allocation is enabled.

Author: Hari Shreedharan <hshreedharan@apache.org>

Closes #8998 from harishreedharan/ss-log-error and squashes the following commits:

462b264 [Hari Shreedharan] Improve log message.
2733d94 [Hari Shreedharan] Minor change to warning message.
eaa48cc [Hari Shreedharan] Log a warning instead of failing the application if dynamic allocation is enabled.
725f090 [Hari Shreedharan] Add config parameter to allow dynamic allocation if the user explicitly sets it.
b3f9a95 [Hari Shreedharan] Disable dynamic allocation and kill app if it is enabled.
a4a5212 [Hari Shreedharan] [streaming] SPARK-10955. Disable dynamic allocation for Streaming applications.

1 files changed, 8 insertions, 1 deletions

diff --git a/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala b/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala
index 94fea63f55..9b2632c229 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala
@@ -44,7 +44,7 @@ import org.apache.spark.streaming.dstream._
 import org.apache.spark.streaming.receiver.{ActorReceiver, ActorSupervisorStrategy, Receiver}
 import org.apache.spark.streaming.scheduler.{JobScheduler, StreamingListener}
 import org.apache.spark.streaming.ui.{StreamingJobProgressListener, StreamingTab}
-import org.apache.spark.util.{CallSite, ShutdownHookManager, ThreadUtils}
+import org.apache.spark.util.{CallSite, ShutdownHookManager, ThreadUtils, Utils}
 
 /**
  * Main entry point for Spark Streaming functionality. It provides methods used to create
@@ -564,6 +564,13 @@ class StreamingContext private[streaming] (
           )
       }
     }
+
+    if (Utils.isDynamicAllocationEnabled(sc.conf)) {
+      logWarning("Dynamic Allocation is enabled for this application. " +
+        "Enabling Dynamic allocation for Spark Streaming applications can cause data loss if " +
+        "Write Ahead Log is not enabled for non-replayable sources like Flume. " +
+        "See the programming guide for details on how to enable the Write Ahead Log")
+    }
   }
 
   /**