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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Updated: (CASSANDRA-876) Support session (read-after-write) consistency
Date Tue, 03 Aug 2010 18:39:22 GMT


Jonathan Ellis updated CASSANDRA-876:

              Summary: Support session (read-after-write) consistency  (was: Support session
consistency (i.e. read after write consistency for clients))
             Assignee: Brian Palmer
        Fix Version/s: 0.7.0
    Affects Version/s:     (was: 0.7.0)
             Priority: Minor  (was: Major)

> Support session (read-after-write) consistency
> ----------------------------------------------
>                 Key: CASSANDRA-876
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Brian Palmer
>            Priority: Minor
>             Fix For: 0.7.0
>         Attachments: CASSANDRA-876.patch
> In and
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 ) 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has some (probably out of date now) code that might be useful here.

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