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Date: Fri, 27 Jun 2014 16:05:24 +0000 (UTC)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12723914.1403801248286.62289.1403885124753@arcas>
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Subject: [jira] [Commented] (CASSANDRA-7453) Geo-replication in Cassandra
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    [ https://issues.apache.org/jira/browse/CASSANDRA-7453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14046097#comment-14046097 ] 

Jonathan Ellis commented on CASSANDRA-7453:
-------------------------------------------

Replicas must be uniquely determined by the partition key and *only* the partition key.  Everything breaks if two different machines compute different replica sets.  Using an additional table might work, but at best you'll have really terrible performance.  So variants on (1) are the only sane option.

> Geo-replication in Cassandra
> ----------------------------
>
>                 Key: CASSANDRA-7453
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7453
>             Project: Cassandra
>          Issue Type: Wish
>            Reporter: Sergio Esteves
>            Priority: Minor
>
> Currently, a Cassandra cluster spanned across different datacenters replicates all data to all datacenters when an update is performed. This is a problem for the scalability of Cassandra as the number of datacenters increases.
> It would be desirable to have some way to make Cassandra aware of the location of data requests so that it could place replicas close to users and avoid replicating to remote datacenters that are far away.
> To this end, we thought of implementing a new replication strategy and some possible solutions to achieve our goals are:
> 1) Using a byte from every row key to identify the location of the primary datacenter where data should be stored (i.e., where it is likely to be accessed).
> 2) Using an additional CF for every row to specify the origin of the data.
> 3) Replicating only to the 2 closest datacenters from the user (for reliability reasons) upon a write update. For reads, a user would try to fetch data from the 2 closest datacenters; if data is not available it would try the other remaining datacenters. If data fails to be retrieved too many times, it means that the client has moved to other part of the planet, and thus data should be migrated accordingly. We could have some problems here, like having the same rows, but with different CFs in different DCs (i.e., if users perform updates to the same rows from different remote places).
> What would be the best way to do this?
> Thanks.


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