[GitHub] [ozone] adoroszlai commented on a diff in pull request #4599: HDDS-8416. ReplicationManager: RatisUnderReplication handler should filter sources by highest BCSID

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

adoroszlai commented on code in PR #4599:
URL: https://github.com/apache/ozone/pull/4599#discussion_r1172940793


##########
hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/RatisUnderReplicationHandler.java:
##########
@@ -217,7 +217,15 @@ private List<DatanodeDetails> getSources(
           }
         })
         .filter(r -> !pendingDeletion.contains(r.getDatanodeDetails()))
-        .sorted((r1, r2) -> r2.getSequenceId().compareTo(r1.getSequenceId()))
+        .collect(Collectors.toList());
+
+    // We should replicate only the max available sequence ID, as replicas with
+    // earlier sequence IDs may be stale copies.
+    long maxSequenceId = availableSources.stream()
+        .map(ContainerReplica::getSequenceId).max(Long::compareTo).orElse(0L);

Review Comment:
   `Long getSequenceId()` may return `null`, so for safety we may add a filter in the stream collecting `availableSources` above.
   
   ```
           .filter(r -> r.getSequenceId() != null)
   ```
   
   Not strictly necessary, as I'm not sure all other code handles `null` gracefully.



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