xyuanlu commented on code in PR #2805:
URL: https://github.com/apache/helix/pull/2805#discussion_r1633654654


##########
meta-client/src/main/java/org/apache/helix/metaclient/impl/zk/ZkMetaClient.java:
##########
@@ -207,16 +208,55 @@ public void set(String key, T data, int version) {
 
   @Override
   public T update(String key, DataUpdater<T> updater) {
-    org.apache.zookeeper.data.Stat stat = new org.apache.zookeeper.data.Stat();
-    // TODO: add retry logic for ZkBadVersionException.
-    try {
-      T oldData = _zkClient.readData(key, stat);
-      T newData = updater.update(oldData);
-      set(key, newData, stat.getVersion());
-      return newData;
-    } catch (ZkException e) {
-      throw translateZkExceptionToMetaclientException(e);
-    }
+    return update(key, updater, false);
+  }
+
+  @Override
+  public T update(String key, DataUpdater<T> updater, boolean retryOnFailure) {
+    final int MAX_RETRY_ATTEMPTS = 3;
+    int retryAttempts = 0;
+    boolean retry;
+    T updatedData = null;
+    do {
+      retry = false;
+      retryAttempts++;
+      try {
+        ImmutablePair<T, Stat> tup = getDataAndStat(key);
+        Stat stat = tup.right;
+        T oldData = tup.left;
+        T newData = updater.update(oldData);
+        set(key, newData, stat.getVersion());
+        updatedData = newData;
+      } catch (MetaClientBadVersionException badVersionException) {
+        // If exceeded max retry attempts, re-throw exception
+        if (retryAttempts >= MAX_RETRY_ATTEMPTS) {
+          LOG.error("Failed to update node at " + key + " after " + 
MAX_RETRY_ATTEMPTS + " attempts.");
+          throw badVersionException;
+        }
+        // Retry on bad version
+        retry = true;
+      } catch (MetaClientNoNodeException noNodeException) {
+        // If node does not exist, attempt to create it - pass null to updater
+        T newData = updater.update(null);
+        if (newData != null) {
+          try {
+            create(key, newData);

Review Comment:
   I would second no creation as well. Say if we try to update "/a/b/c" and get 
no node exception, we just fail immediately. 



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