Hi Tsz-Wo, I have one question that may be a bit out of topic:
When a new node join an existing cluster in this case, how it exactly applies logs? Will it applies raft logs from the beginning one by one? TiKV will sends a snapshot of state machine from leader to the new node in this case to speed up the catch up progress and I'd like to know how Ratis implements catch-up. Best, tison. Tsz Wo Sze <[email protected]> 于2022年7月2日周六 01:31写道： > > * It's possible to update the old configuration first by using > client.admin().setConfiguration(), let's say set N=11 first, then start new > nodes. However, since 5 < 11/2, the cluster won't be able to elect leader > until at least 1 new node join. > Yes, you are right. Also, even if one node has joined, the group has to > wait for it to catch up with the previous log entries in order to obtain a > majority for committing new entries. > > > * Or may be we should limit the count when scaling? From N=5 -> N=7 -> > N=9 -> N=11. > > We may start the 6 new nodes as listeners first. Listeners receive log > entries but they are not voting members and they won't be counted for > majority. When the listeners catch up, we may change them to normal nodes > so that they become voting members. > > Tsz-Wo > > > On Fri, Jul 1, 2022 at 10:23 AM Tsz Wo Sze <[email protected]> wrote: > >> Hi Riguz, >> >> > Start 6 new nodes with new configuration N=11, while keeping the >> previous nodes running >> >> This step probably won't work as expected since it will create a new >> group but not adding nodes to the original group. We must use the >> setConfiguration API to change configuration (add/remove nodes); see >> https://github.com/apache/ratis/blob/bd83e7d7fd41540c8bda6bd92a52ac99ccec2076/ratis-client/src/main/java/org/apache/ratis/client/api/AdminApi.java#L35 >> >> Hope it helps. Thanks a lot for trying Ratis! >> >> Tsz-Wo >> >> On Fri, Jul 1, 2022 at 12:30 AM Riguz Lee <[email protected]> wrote: >> >>> >>> >>> Hi, >>> >>> >>> I'm testing scaling up/down the raft cluster, but ratis is not working >>> as expected in new cluster. My steps are: >>> >>> >>> * Initialize a cluster with 5 nodes, the size and peers of the cluster >>> is configured in a configuration file, let's say N=5. The cluster works >>> perfectly, raft logs are synchronized across the cluster. >>> >>> * Start 6 new nodes with new configuration N=11, while keeping the >>> previous nodes running >>> >>> * Recreate the previous nodes with N=11 one by one >>> >>> >>> According the raft paper, raft should be able to handle configuration >>> change by design, but after the above steps, what I've found is that: >>> >>> >>> - New nodes not able to join the cluster >>> >>> - Old nodes still has a size of 5(by >>> *client.getGroupManagementApi(peerId).info(groupId)*) >>> >>> >>> So how should I scale the cluster correctly? A few thoughts of mine: >>> >>> >>> * Definitely the old cluster should not be stopped while starting new >>> nodes, otherwise new nodes might be able to elect new leader(eg. N=11 with >>> 6 new nodes) and raft logs in old nodes will be overriden. >>> >>> * It's possible to update the old configuration first by using >>> client.admin().setConfiguration(), let's say set N=11 first, then start new >>> nodes. However, since 5 < 11/2, the cluster won't be able to elect leader >>> until at least 1 new node join. >>> >>> * Or may be we should limit the count when scaling? From N=5 -> N=7 -> >>> N=9 -> N=11. >>> >>> >>> Thanks, >>> >>> Riguz Lee >>> >>> >>> >>>
