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Date: Mon, 5 Oct 2015 18:43:28 +0000 (UTC)
From: "Oliver Seiler (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-9602) EACH_QUORUM READ support needed
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    [ https://issues.apache.org/jira/browse/CASSANDRA-9602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14943807#comment-14943807 ] 

Oliver Seiler commented on CASSANDRA-9602:
------------------------------------------

As the author of CASSANDRA-6970, I'm interested in this having a different outcome; I would still like EACH_QUORUM READs, as it would eliminate relying on CL=ALL in some places. I have a similar use-case as the reporter (doing CL=EACH_QUORUM writes is just out of the question for our environments...)

> In (certain) versions 2.0 this was supported:

It has never been supported, AFAIK; the docs for 2.0 are wrong, something I complained about a lot to whomever could stand my ranting (you get an error in 2.0 trying to run an EACH_QUORUM read).

> EACH_QUORUM READ support needed
> -------------------------------
>
>                 Key: CASSANDRA-9602
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9602
>             Project: Cassandra
>          Issue Type: Sub-task
>            Reporter: Scott Guminy
>            Assignee: Carl Yeksigian
>              Labels: client-impacting, doc-impacting
>             Fix For: 3.x
>
>
> EACH_QUORUM consistency for READ should be added.
> This bug https://issues.apache.org/jira/browse/CASSANDRA-3272 says it is not needed ever, however I have a use case where I need it.  I think the decision made was incorrect. Here's why...
>  
>  My application has two key pieces:
>  
>  # *End user actions* which add/modify data in the system.  End users typically access the application from only one Data Center and only see their own data
> # *Scheduled business logic tasks* which run from any node in any data center.  These tasks process data added by the end users in an asynchronous way
>  
>  *End user actions must have the highest degree of availability.*  Users must always be able to add data to the system.  The data will be processed later.  To support this, end user actions will use *LOCAL_QUORUM Read and Write Consistency*.
>  
>  Scheduled tasks don't need to have a high degree of availability but MUST operate on the most up to date data.  *The tasks will run with EACH_QUORUM* to ensure that no matter how many data centers we have, we always READ the latest data.  This approach allows us some amount of fault tolerance. 
>  
>  The problem is that EACH_QUORUM is not a valid READ consistency level.  This mean I have no alternative but to use ALL.  ALL will work, but is not the best since it offers support for ZERO failures.  I would prefer EACH_QUORUM since it can support some failures in each data center.


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