add docs for the configuration

Author: functioner

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -5050,6 +5050,19 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.namenode.edits.async.logsyncnotify.executor.size</name>
+  <value>10</value>
+  <description>
+    The size of the thread pool executing logSyncNotify in FSEditLogAsync.
+    This thread pool decouples the RPC response network sending from
+    the FSEditLogAsync thread so that FSEditLogAsync would not be affected
+    by the potential network hanging issue (HDFS-15869).
+    This property defaults to 10.
+  </description>
+</property>
+
+
 <property>
   <name>dfs.namenode.edits.dir.minimum</name>
   <value>1</value>