[jira] [Commented] (IOTDB-460) [Distributed]Remove data of outdated slots

["WangChao (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IOTDB-460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17070677#comment-17070677 ] 

WangChao commented on IOTDB-460:
--------------------------------

I think slot could has three info like following.

slot -> (state, source, destination)
state -> normal, rebalance

when a slot is rebalancing, it has following info.

slot -> (rebalance, source, destination)


when destination finished pulling the slot, it should start a raft log to chang the slot state from rebalance to normal.

slot -> (normal, source, null)


source should check the slot's state, if slot is normal and source is not owned by him, it could delete it.


So, we only support a change once time, like delete a node or add a node. Only when all slots finished tranfer, we could do next change.

> [Distributed]Remove data of outdated slots
> ------------------------------------------
>
>                 Key: IOTDB-460
>                 URL: https://issues.apache.org/jira/browse/IOTDB-460
>             Project: Apache IoTDB
>          Issue Type: Improvement
>            Reporter: Tian Jiang
>            Priority: Major
>              Labels: data-transfer, distributed
>
> In node addition/removal, the slots managed by a node will change. However, the data of corresponding slots cannot be removed yet because the new holders of the slots will pull such data to themselves. As the data pulling is issued by the new holders randomly, it is hard for the previous holders to find out when will the data be needless. As a result, the previous holder cannot delete the local data with confidence.
> It will be necessary to find a way for the previous holders to know when the data has been replicated to the new holders so that they will be able to remove the local data.



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