Adds references to KeyCommitTooLargeException docs whever we throw th…

…e exception and also mentions --experiments=throw_exceptions_on_large_output as an option.

runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/OutputTooLargeException.java

@@ -22,7 +22,9 @@
 /** Indicates that an output element was too large. */
 public class OutputTooLargeException extends RuntimeException {
   public OutputTooLargeException(String reason) {
-    super(reason);
+    super(
+        reason
+            + " See https://cloud.google.com/dataflow/docs/guides/common-errors#key-commit-too-large-exception.");
   }
 
   /** Returns whether an exception was caused by a {@link OutputTooLargeException}. */

runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillSink.java

@@ -183,7 +183,9 @@ public long add(WindowedValue<T> data) throws IOException {
               "Trying to output too large key with size "
                   + key.size()
                   + ". Limit is "
-                  + context.getMaxOutputKeyBytes());
+                  + context.getMaxOutputKeyBytes()
+                  + ". See https://cloud.google.com/dataflow/docs/guides/common-errors#key-commit-too-large-exception."
+                  + " Running with --experiments=throw_exceptions_on_large_output will instead throw an OutputTooLargeException which may be caught in user code.");
         }
       }
       if (value.size() > context.getMaxOutputValueBytes()) {
@@ -194,7 +196,9 @@ public long add(WindowedValue<T> data) throws IOException {
               "Trying to output too large value with size "
                   + value.size()
                   + ". Limit is "
-                  + context.getMaxOutputValueBytes());
+                  + context.getMaxOutputValueBytes()
+                  + ". See https://cloud.google.com/dataflow/docs/guides/common-errors#key-commit-too-large-exception."
+                  + " Running with --experiments=throw_exceptions_on_large_output will instead throw an OutputTooLargeException which may be caught in user code.");
         }
       }
 

runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/streaming/KeyCommitTooLargeException.java

@@ -40,7 +40,8 @@ public static KeyCommitTooLargeException causedBy(
     message.append(
         ". This may be caused by grouping a very "
             + "large amount of data in a single window without using Combine,"
-            + " or by producing a large amount of data from a single input element.");
+            + " or by producing a large amount of data from a single input element."
+            + " See https://cloud.google.com/dataflow/docs/guides/common-errors#key-commit-too-large-exception.");
     return new KeyCommitTooLargeException(message.toString());
   }