xBis7 commented on code in PR #5726:
URL: https://github.com/apache/ozone/pull/5726#discussion_r1427902450
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hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/SCMCommonPlacementPolicy.java:
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@@ -445,6 +445,7 @@ public ContainerPlacementStatus validateContainerPlacement(
}
}
List<Integer> currentRackCount = new ArrayList<>(dns.stream()
+ .filter(d -> !(d.isDecommissioned()))
Review Comment:
@sodonnel I've been looking into your suggestion. With that change, we will
be ignoring mis-replication for every over-replicated container.
Let's say we have this scenario
* RackAware policy
* 7 datanodes, 3 are IN_SERVICE, 4 are offline
* 2 of the offline nodes get back IN_SERVICE
* Now we have, 5 nodes IN_SERVICE, 2 offline
* 5 available replicas and we only need 3, so the container is
over-replicated
Initially
```
/rack0/node0 -> in_service - used
/rack0/node1 -> in_service - used
/rack0/node2 -> offline
/rack0/node3 -> offline
/rack0/node4 -> offline
/rack1/node5 -> in_service - used
/rack1/node6 -> offline
```
After 2 offline coming back
```
/rack0/node0 -> in_service - used
/rack0/node1 -> in_service - used
/rack0/node2 -> offline -> in_service - used
/rack0/node3 -> offline
/rack0/node4 -> offline
/rack1/node5 -> in_service - used
/rack1/node6 -> offline -> in_service - used
```
The placement will be [3, 2] where we need [2, 1]. The container is
mis-replicated but because we adjust the maxReplica number by adding the
replicaDelta, we get that the policy is satisfied.
`maxReplicaPerRack = 2`
`dns.size() = 7`
`replicas = 3`
`Math.max(0, dns.size() - replicas) = Math.max(0, 4) = 4` regardless of
whether the excessive replicas are healthy or not.
`maxReplicaPerRack = 6`
Even if we add a check to increase the maxReplica number, only if there are
decommission or maintenance nodes, it won't make a difference. We can't
distinguish between replicas on offline nodes and replicas on online nodes.
This approach will effectively ignore `mis-replication` when caused by
`over-replication`.
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