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From "Jun Rao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-197) Expose ring map to client for more direct access
Date Fri, 22 May 2009 17:25:45 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-197?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12712176#action_12712176
] 

Jun Rao commented on CASSANDRA-197:
-----------------------------------

If you look at the original Dynamo paper, it definitely talks about exposing key locations
for shorter network path.

You can think of RingCache part of the cassandra client library. It's just a cache and only
serves as hints. Note that bigtable/Hbase expose the locality to clients too. Ideally, such
exposure should be hidden in the client library. However, this is a bit hard to do in Cassandra
since the client code is generated by Thrift. In any case, I don't see any harm for exposing
such information.

As for the endpoint_for_key call, this will force the client to cache the location for every
row, which is likely more expensive.



> Expose ring map to client for more direct access
> ------------------------------------------------
>
>                 Key: CASSANDRA-197
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-197
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Jun Rao
>            Assignee: Jun Rao
>         Attachments: issue197.patchv1
>
>
> For certain applications, it would be nice if a read is sent to a node that owns the
data locally. This saves an extra network hop. To do that, a client will need to cache the
ring map and use it to figure out the nodes owning a row.

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