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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9602) EACH_QUORUM READ support needed
Date Wed, 07 Oct 2015 20:02:27 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14947482#comment-14947482
] 

Ariel Weisberg commented on CASSANDRA-9602:
-------------------------------------------

OK sounds good. +1.

I guess each node will distribute queries to different quorums and if the clients are load
balancing correctly load should be somewhat even. The clients can present even load, but depending
on how the nodes behave that could create hotspots especially at low cardinalities. It's easy
enough to throw in a shuffle and then run it through cstar perf, but that is out of scope
for this ticket.

> 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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