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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Created: (CASSANDRA-876) Support session consistency
Date Wed, 10 Mar 2010 19:35:27 GMT
Support session consistency
---------------------------

                 Key: CASSANDRA-876
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-876
             Project: Cassandra
          Issue Type: New Feature
          Components: Core
            Reporter: Jonathan Ellis


In http://www.allthingsdistributed.com/2007/10/amazons_dynamo.html and http://www.allthingsdistributed.com/2008/12/eventually_consistent.html
Amazon discusses the concept of "eventual consistency."  Cassandra uses eventual consistency
in a design similar to Dynamo.

Supporting session consistency would be useful and relatively easy to add: we already have
the concept of a Memtable (see http://wiki.apache.org/cassandra/MemtableSSTable ) to "stage"
updates in before flushing to disk; if we applied mutations to a session-level memtable on
the coordinator machine (that is, the machine the client is connected to), and then did a
final merge from that table against query results before handing them to the client, we'd
get it almost for free.

Of course, the devil is in the details; thrift doesn't provide any hooks for session-level
data out of the box, but we could do this with a threadlocal approach fairly easily.  CASSANDRA-569
has some (probably out of date now) code that might be useful here.

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