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From "Scott Guminy (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-9602) EACH_QUORUM READ support needed
Date Tue, 16 Jun 2015 12:15:00 GMT
Scott Guminy created CASSANDRA-9602:

             Summary: EACH_QUORUM READ support needed
                 Key: CASSANDRA-9602
             Project: Cassandra
          Issue Type: Bug
            Reporter: Scott Guminy

EACH_QUORUM consistency for READ should be added.

This bug says it is not needed ever,
however I have a use case where I need it.  I think the decision made in this defect is 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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