[infinispan-issues] [JBoss JIRA] (ISPN-5021) Nodes that finish the rebalance later can see outdated values

[Pedro Ruivo (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-5021?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13028401#comment-13028401 ] 

Pedro Ruivo commented on ISPN-5021:
-----------------------------------

[~dan.berindei], I don't think we need to remove the old entries and ignore the writes in the 2nd topology update. I think the data will be kept consistency and we avoid some checking in which state we are. 

> Nodes that finish the rebalance later can see outdated values
> -------------------------------------------------------------
>
>                 Key: ISPN-5021
>                 URL: https://issues.jboss.org/browse/ISPN-5021
>             Project: Infinispan
>          Issue Type: Bug
>          Components: Core, State Transfer
>    Affects Versions: 7.0.2.Final
>            Reporter: Dan Berindei
>            Assignee: Pedro Ruivo
>            Priority: Critical
>             Fix For: 7.1.0.Beta1
>
>
> Copied from [ISPN-4444|https://issues.jboss.org/browse/ISPN-4444?focusedCommentId=13022645#comment-13022645]
> If the CH_UPDATE command is delayed on the old owner, the new owners might update the key without the old owner knowing, and a locality check on the old owner won't help.
> I remember one thing that struck me when reading the Raft algorithm was that they install configuration changes symmetrically, in 3 phases. We might need to do the same for our rebalance: start a rebalance with read_ch=old, write_ch=old+new, when the new owners have all the data install read_ch=new, write_ch=old+new, and finally read_ch=new, write_ch=new. Old cache entries are removed during the 2nd topology update, and further writes should be ignored, in order for this to work.



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