[infinispan-issues] [JBoss JIRA] (ISPN-3918) Inconsistent view of the cache with putIfAbsent in a non-tx cache during state transfer

[Radim Vansa (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-3918?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13380769#comment-13380769 ] 

Radim Vansa commented on ISPN-3918:
-----------------------------------

This situation can happen with triangle algorithm even without any topology change; as primary does not hold the lock during replication, second putIfAbsent may fail before the first putIfAbsent is executed on backup.

> Inconsistent view of the cache with putIfAbsent in a non-tx cache during state transfer
> ---------------------------------------------------------------------------------------
>
>                 Key: ISPN-3918
>                 URL: https://issues.jboss.org/browse/ISPN-3918
>             Project: Infinispan
>          Issue Type: Bug
>          Components: Core, State Transfer
>    Affects Versions: 6.0.0.Final
>            Reporter: Dan Berindei
>              Labels: consistency
>             Fix For: 9.0.0.Final
>
>         Attachments: ntpiadjst.log.gz
>
>
> In a non-tx cache, sometimes it's possible for a {{get(k)}} to return {{null}} even though a previous {{putIfAbsent(k, v)}} returned a non-null value and the only concurrent operations on the cache are concurrent putIfAbsent calls.
> Say \[B, A, C] are the owners of k (C just joined)
> 1. A starts a {{putIfAbsent(k, v1)}} command, sends it to B
> 2. B forwards the command to A and C
> 3. C writes {{k=v1}} 
> 4. C becomes the primary owner of k (owners are now  \[C, A])
> 5. A/B see the new topology before committing and throw an outdatedTopologyException
> 6. A retries the command, sends it to C
> 7. C forwards the command to A, which writes {{k=v1}}
> 8. C doesn't have to update the entry, returns null
> If, between steps 3 and 7, another thread on A starts a {{putIfAbsent(k, v2)}} command, the command will fail and return {{v1}} (because the primary owner already has a value). However, a subsequent {{get(k)}} command will return {{null}}, because A is an owner and doesn't have the value.



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