[infinispan-issues] [JBoss JIRA] Commented: (ISPN-1275) Virtual nodes producing same hash id for two different cluster nodes

[Dan Berindei (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-1275?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12617466#comment-12617466 ] 

Dan Berindei commented on ISPN-1275:
------------------------------------

I got it now, if we have a collision (A and B should both get hash id 100, B is moved to 101) and then A leaves, B will get id 100 unless we somehow remember that B was assigned position 101 before.

The problem is that not all nodes will have the same chain of CHs, if we have a cluster {A, B} and B and C join in rapid succession A may see ch_0 = {A, B}, ch_1 = {A, B, C}, ch_2 = {A, B, C, D}, while B might see only ch_0 = {A, B} and ch_1 = {A, B, C, D}.

Reassigning to Manik, it turns out the fix isn't the one-liner in AbstractWheelConsistentHash I was thinking of...

> Virtual nodes producing same hash id for two different cluster nodes
> --------------------------------------------------------------------
>
>                 Key: ISPN-1275
>                 URL: https://issues.jboss.org/browse/ISPN-1275
>             Project: Infinispan
>          Issue Type: Bug
>          Components: Distributed Cache
>    Affects Versions: 5.0.0.CR8
>            Reporter: Galder Zamarreño
>            Assignee: Dan Berindei
>            Priority: Blocker
>             Fix For: 5.0.0.FINAL
>
>         Attachments: hashids.log
>
>
> While working on ISPN-1273, I've discovered that when virtual nodes are enabled, ConsistentHash.getHashIds(address) can return the same hash for two different cluster nodes. Example: with 500 virtual nodes, both NodeA-23181 and NodeB-39177 produce hash id *5289*. See attached log.

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