db2

This post is one part of a series discussing the OpenStack Nova Juno mid-cycle meetup. It's a bit shorter than most of the others, because the next thing on my list to talk about is DB2, and that's relatively contained. IBM is interested in adding DB2 support as a SQL database for Nova. Theoretically, this is a relatively simple thing to do because we use SQLAlchemy to abstract away the specifics of the SQL engine. However, in reality, the abstraction is leaky. The obvious example in this case is that DB2 has different rules for foreign keys than other SQL engines we've used. So, in order to be able to make this change, we need to tighten up our schema for the database. The change that was discussed is the requirement that the UUID column on the instances table be not null. This seems like a relatively obvious thing to allow, given that UUID is the official way to identify an instance, and has been for a really long time. However, there are a few things which make this complicated: we need to understand the state of databases that might have been through a long chain of upgrades from previous…