英文:
What will happen if I reduce RF from 5 to 3 then decommission 2 of 5 nodes?
问题
我有一个包含5个节点的 Scylla 集群，我的 keyspace 的复制因子也是5。现在我想从集群中移除2个节点。
我计划将复制因子从5更改为3，并取消2个节点。我可以在不进行维护的情况下执行此操作吗？
一个安全且平稳的在线修改是我期望的... 😄
英文:
I have a scylla cluster which has 5 nodes and my keyspace's replication factor is also 5. Now I want to remove 2 nodes from the cluster.
I plan to change the replication factor from 5 to 3, and decommission 2 nodes. Can I take this operation without a maintenance?
A safe and smooth online modification is what I expected ... 😄
答案1
得分: 2
减少副本数量不需要停机。当节点退役时，只要环中剩余足够的副本并且有足够的容量处理应用程序流量，也不需要停机。
需要考虑的重要事项是定期修复集群（确保副本一致性）并且节点不会因为丢失的变异而受到影响，因为这表明节点被过载。
如果在节点退役之前容量不足，当节点减少时情况会变得更糟，因为集群的容量也会下降，这将导致应用程序的正常操作受到干扰，甚至可能出现服务中断。祝好！
英文:
Reducing the replica count doesn't require downtime. Decommissioning nodes doesn't require downtime either as long as there are sufficient replicas left in the ring plus there is sufficient capacity left to handle the application traffic.
The important thing to consider is that the cluster is repaired regularly (to make sure that the replicas are consistent) and that the nodes do not suffer from dropped mutations because it is an indication that nodes are overloaded.
If there isn't sufficient capacity BEFORE nodes are decommissioned, the situation will be even worse when there are less nodes because the capacity of the cluster will also drop so there will be a disruption to the normal operation of your application or worse, a service outage. Cheers!
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