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From "Davide Giannella (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-2472) Add support for atomic counters on cluster solutions
Date Wed, 16 Dec 2015 08:16:46 GMT

    [ https://issues.apache.org/jira/browse/OAK-2472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15059679#comment-15059679
] 

Davide Giannella commented on OAK-2472:
---------------------------------------

[~lbyrum]
bq. So we have a couple of use cases where it is highly expected that we can have multiple
threads updating the same count

It should not be an issue at all. Our ITs cover an update of the same counter from 100 concurrent
threads. There should not be any failures and no need to deal with locks that would not than
scale. Of course if anything breaks, please report.

https://github.com/apache/jackrabbit-oak/blob/trunk/oak-jcr/src/test/java/org/apache/jackrabbit/oak/jcr/AtomicCounterIT.java#L60

bq. Alternately, we saw in the docs and code that there were some plans where not just oak:increment
was recognized, but oak:increment-UUID was recognized.

What docs are you referring to? Please ignore any technical details attached to jira issues
as they are implementation details on who Oak achieve the atomic counter. From an end-user
POV the only docs so far are the javadoc. Will produce some more docs once the feature will
be completed for cluster.

http://jackrabbit.apache.org/oak/docs/apidocs/org/apache/jackrabbit/oak/plugins/atomic/AtomicCounterEditor.html

[~masonw]

bq. If you look at the attached spec from OAK-2220...

Don't. That's a summary of discussions we, oak team, had in order to approach the problem.
They are technical details and as a end-user you should not be worried about those.

bq. That said, if thread1 sets oak:increment to 1 and thread2 simultaneously sets oak:increment
to 2, then regardless of which order they actually commit in, since oak:increment is never
actually saved, but just used to update oak:counter, I think the result will always be oak:counter+=3

yes it is.

> Add support for atomic counters on cluster solutions
> ----------------------------------------------------
>
>                 Key: OAK-2472
>                 URL: https://issues.apache.org/jira/browse/OAK-2472
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.3.0
>            Reporter: Davide Giannella
>            Assignee: Davide Giannella
>              Labels: scalability
>             Fix For: 1.4
>
>         Attachments: atomic-counter.md
>
>
> As of OAK-2220 we added support for atomic counters in a non-clustered situation. 
> This ticket is about covering the clustered ones.



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