[openstack-dev] [nova][object] One question to the resource tracker session
dms at danplanet.com
Thu Nov 14 18:43:14 UTC 2013
>> You're right, it's not really achievable without moving to a schemaless
>> persistence model. I'm fairly certain it was added to be humorous and
>> should not be considered an outcome of that session.
> But we can avoid most data migrations by adding any required
> conversion code into the objects DB layer, once we start using it. But
> it might not be what we want.
Right, I'm sure it was added to the notes in response to discussion in
the room about hating migrations in general. We can't avoid them
entirely, but we do need to start moving away from making them
monolithic and scary. This is important not only for performance when
running migrations on large databases, but also for live upgrade. The
general agreement from the summit sessions was that we need to make
conductor able to tolerate all the schema versions from N-1 to N (where
N is a release) so that it can be upgraded first, the schema next, and
then (when possible) data migrations happen live instead of in bulk.
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