[SPARK-21530] Update description of spark.shuffle.maxChunksBeingTransferred.

## What changes were proposed in this pull request?

Update the description of `spark.shuffle.maxChunksBeingTransferred` to include that the new coming connections will be closed when the max is hit and client should have retry mechanism.

Author: jinxing <jinxing6042@126.com>

Closes #18735 from jinxing64/SPARK-21530.

common/network-common/src/main/java/org/apache/spark/network/util/TransportConf.java

@@ -258,7 +258,11 @@ public class TransportConf {
   }
 
   /**
-   * The max number of chunks allowed to being transferred at the same time on shuffle service.
+   * The max number of chunks allowed to be transferred at the same time on shuffle service.
+   * Note that new incoming connections will be closed when the max number is hit. The client will
+   * retry according to the shuffle retry configs (see `spark.shuffle.io.maxRetries` and
+   * `spark.shuffle.io.retryWait`), if those limits are reached the task will fail with fetch
+   * failure.
    */
   public long maxChunksBeingTransferred() {
     return conf.getLong("spark.shuffle.maxChunksBeingTransferred", Long.MAX_VALUE);

docs/configuration.md

@@ -635,7 +635,11 @@ Apart from these, the following properties are also available, and may be useful
   <td><code>spark.shuffle.maxChunksBeingTransferred</code></td>
   <td>Long.MAX_VALUE</td>
   <td>
-    The max number of chunks allowed to being transferred at the same time on shuffle service.
+    The max number of chunks allowed to be transferred at the same time on shuffle service.
+    Note that new incoming connections will be closed when the max number is hit. The client will
+    retry according to the shuffle retry configs (see <code>spark.shuffle.io.maxRetries</code> and
+    <code>spark.shuffle.io.retryWait</code>), if those limits are reached the task will fail with
+    fetch failure.
   </td>
 </tr>
 <tr>