[infinispan-issues] [JBoss JIRA] (ISPN-3422) In non-tx caches, write operations may not be atomic during rebalance

[Dan Berindei (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-3422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12824590#comment-12824590 ] 

Dan Berindei commented on ISPN-3422:
------------------------------------

Yes, we should be able to fix this by comparing the PutIfAbsentCommand's value with the value that exists in the data container even when ignorePreviousValue is set to true. If the value in the data container is either null or the same, then the command should succeed, otherwise it should fail.

I didn't implement this back when fixing ISPN-3357 because of 2 reasons:
1) Values would have to implement equals() for this to work. AFAICT we don't really support versioning in non-tx mode.
2) We should only do the comparison check on the primary, because we want the final value to be the same on all the owners even if there was an inconsistency before. So we'd need to inject a {{ClusteringDependentLogic}}  in all the conditional commands.
                
> In non-tx caches, write operations may not be atomic during rebalance
> ---------------------------------------------------------------------
>
>                 Key: ISPN-3422
>                 URL: https://issues.jboss.org/browse/ISPN-3422
>             Project: Infinispan
>          Issue Type: Bug
>            Reporter: Dan Berindei
>            Assignee: Dan Berindei
>            Priority: Critical
>              Labels: jdg62blocker
>             Fix For: 6.0.0.CR2, 6.0.0.Final
>
>
> If the cache topology changes while a write command is running and before it has actually committed the entry to the data container, we retry the command (see ISPN-3366 and ISPN-3357). But before we detect the topology change, one or more of the backup owners may have already applied the modification.
> Retrying the command re-acquires the key lock on the primary owner (even if the primary owner didn't change). That means another command could have modified the same key in the meantime, but the retried command is going to ignore any changes and is going to return the value before the first attempt. Obviously, the command is not retried if the first attempt is not successful, but scenarios like this are possible:
> {code}
> thread 1: putIfAbsent(k, v1) -> null
> thread 2: putIfAbsent(k, v2) -> null
> {code}

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