[GitHub] [hadoop] simbadzina commented on a diff in pull request #5990: HDFS-17166. RBF: Throwing NoNamenodesAvailableException for a long time, when failover

["simbadzina (via GitHub)" <gi...@apache.org>]

simbadzina commented on code in PR #5990:
URL: https://github.com/apache/hadoop/pull/5990#discussion_r1309343672


##########
hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MembershipNamenodeResolver.java:
##########
@@ -478,4 +478,40 @@ private List<MembershipState> getRecentRegistrationForQuery(
   public void setRouterId(String router) {
     this.routerId = router;
   }
+
+  /**
+   * Rotate cache, make the current namenode have the lowest priority,
+   * to ensure that the current namenode will not be accessed first next time.
+   *
+   * @param nsId name service id
+   * @param namenode namenode contexts
+   */
+  @Override
+  public synchronized void rotateCache(String nsId, FederationNamenodeContext namenode) {
+    cacheNS.compute(Pair.of(nsId, false), (ns, namenodeContexts) -> {

Review Comment:
   I think we need to refresh the cache for the key `Pair.of(nsId, true)` at times.
   
   You can extend the signature of rotateCache to 
   ```java
   public synchronized void rotateCache(String nsId, FederationNamenodeContext namenode, boolean listObserversFirst)
   ```
   
   And then call it with
   ```java
   this.namenodeResolver.rotateCache(nsId, namenode, shouldUseObserver);
   ```
   



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