[jira] [Created] (CASSANDRA-8990) Allow clients to override the DCs the data gets sent to, per write request, overriding keyspace settings

["Donald Smith (JIRA)" <ji...@apache.org>]

Donald Smith created CASSANDRA-8990:
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             Summary: Allow clients to override the DCs the data gets sent to, per write request, overriding keyspace settings
                 Key: CASSANDRA-8990
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8990
             Project: Cassandra
          Issue Type: New Feature
            Reporter: Donald Smith


Currently each keyspace specifies how many replicas to write to each data center. In CQL one specifies:
{noformat}
 WITH replication = {
  'class': 'NetworkTopologyStrategy',
  'DC1: '3',
  'DC2': '3'
}
{noformat}
But in some use cases there's no need to write certain rows to a certain datacenter.  Requiring the user to create two keyspaces is burdensome and complicates code and queries.  

For example, we have global replication of our data to multiple continents. But we want the option to send only certain rows globally with certain values for certain columns -- e.g., only for users that visited that country).

Cassandra and CQL should support the ability of client code to specify, on a per request basis, that a write should go only to specified data centers. 




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