HDFS-15356. Unify configuration `dfs.ha.allow.stale.reads` to DFSConfigKeys. Contributed by Xiaoqiao He.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -1164,6 +1164,9 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
       "dfs.ha.nn.not-become-active-in-safemode";
   public static final boolean DFS_HA_NN_NOT_BECOME_ACTIVE_IN_SAFEMODE_DEFAULT =
       false;
+  public static final String DFS_HA_ALLOW_STALE_READ_KEY =
+      "dfs.ha.allow.stale.reads";
+  public static final boolean DFS_HA_ALLOW_STALE_READ_DEFAULT = false;
 
   // Security-related configs
   public static final String DFS_ENCRYPT_DATA_TRANSFER_KEY = "dfs.encrypt.data.transfer";

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/HAUtil.java

@@ -17,6 +17,8 @@
  */
 package org.apache.hadoop.hdfs;
 
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_HA_ALLOW_STALE_READ_DEFAULT;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_HA_ALLOW_STALE_READ_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_HA_NAMENODE_ID_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_HTTPS_ADDRESS_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_HTTPS_BIND_HOST_KEY;
@@ -220,11 +222,12 @@ public class HAUtil {
    * @return true if the NN should allow read operations while in standby mode.
    */
   public static boolean shouldAllowStandbyReads(Configuration conf) {
-    return conf.getBoolean("dfs.ha.allow.stale.reads", false);
+    return conf.getBoolean(DFS_HA_ALLOW_STALE_READ_KEY,
+        DFS_HA_ALLOW_STALE_READ_DEFAULT);
   }
   
   public static void setAllowStandbyReads(Configuration conf, boolean val) {
-    conf.setBoolean("dfs.ha.allow.stale.reads", val);
+    conf.setBoolean(DFS_HA_ALLOW_STALE_READ_KEY, val);
   }
 
   /**

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

@@ -4602,6 +4602,15 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.ha.allow.stale.reads</name>
+  <value>false</value>
+  <description>
+    If true, a NameNode in Standby state can process read request and the result
+    could be stale.
+  </description>
+</property>
+
 <property>
   <name>dfs.journalnode.edits.dir</name>
   <value>/tmp/hadoop/dfs/journalnode/</value>