[openstack-dev] More on the topic of DELIMITER, the Quota Management Library proposal

Edward Leafe ed at leafe.com
Sun Apr 24 00:20:35 UTC 2016

On Apr 23, 2016, at 3:10 PM, Jay Pipes <jaypipes at gmail.com <mailto:jaypipes at gmail.com>> wrote:

> BTW, note to Ed Leafe... unless your distributed data store supports transactional semantics, you can't use a distributed data store for these types of solutions. Instead, you will need to write a whole bunch of code that does post-auditing of claims and quotas and a system that accepts that oversubscription and out-of-sync quota limits and usages is a fact of life. 

Yes, that was one of the things that I liked about Cassandra: http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0 <http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0>

For instance, in the scheduler, making a claim would simply fail if another process had changed any of the resources in question, as the transaction would not be allowed.

> Not to mention needing to implement JOINs in Python.

Heh, JOIN in a column family database is not needed. You do have to think about data a lot differently, and that means unlearning everything you know about normalization. As a long-time SQL DB admin, it took my brain quite some time to be able to understand the different approach.

-- Ed Leafe
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