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From "Michael Shuler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9602) EACH_QUORUM READ support needed
Date Wed, 08 Jul 2015 18:20:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14619094#comment-14619094
] 

Michael Shuler commented on CASSANDRA-9602:
-------------------------------------------

The 2.0 branch is in maintenance and the latest released version is 2.0.16.
The 2.1 branch, while relatively new, is also in maintenance.
The 2.2 branch is up for a first release soon - RC1 has been out for a few weeks - RC2 is
up for vote.

I suppose it's possible this could go into 2.2, but that would be up to the developers.

Basically, new features go into the development branch, trunk, which will become 3.0. This
is a new CQL spec feature request, although it may be considered relatively minor. I can guarantee
this won't go into a 2.0 release.

> EACH_QUORUM READ support needed
> -------------------------------
>
>                 Key: CASSANDRA-9602
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9602
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Scott Guminy
>            Assignee: Tyler Hobbs
>             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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