adoroszlai commented on code in PR #4599:
URL: https://github.com/apache/ozone/pull/4599#discussion_r1173439504
##########
hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/RatisUnderReplicationHandler.java:
##########
@@ -217,7 +217,18 @@ 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(r -> {
+ Long seqId = r.getSequenceId();
+ return seqId == null ? Long.valueOf(0L) : seqId;
+ }).max(Long::compareTo).orElse(0L);
+
+ return availableSources.stream()
+ .filter(r -> r.getSequenceId() == maxSequenceId)
Review Comment:
This comparison may still produce NPE if `r.getSequenceId()` is `null`, due
to auto-unboxing (converted to `long` for comparison).
```
java.lang.NullPointerException
at
org.apache.hadoop.hdds.scm.container.replication.RatisUnderReplicationHandler.lambda$getSources$5(RatisUnderReplicationHandler.java:231)
at
java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174)
at
java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1384)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at
java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at
java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at
java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566)
at
org.apache.hadoop.hdds.scm.container.replication.RatisUnderReplicationHandler.getSources(RatisUnderReplicationHandler.java:233)
```
The following is safe (tested with all non-nulls, mixed, all nulls):
```suggestion
OptionalLong maxSequenceId = availableSources.stream()
.filter(r -> r.getSequenceId() != null)
.mapToLong(ContainerReplica::getSequenceId)
.max();
Stream<ContainerReplica> replicaStream = availableSources.stream();
if (maxSequenceId.isPresent()) {
replicaStream = replicaStream
.filter(r -> r.getSequenceId() != null)
.filter(r -> r.getSequenceId() == maxSequenceId.getAsLong());
}
return replicaStream
```
Note: some new imports are needed for it to compile.
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