Open Stack

> I tested a code change that essentially reverts
> https://review.openstack.org/#/c/276861/1/nova/api/metadata/base.py
>
> In other words, with this change metadata tables are not fetched by
> default in API requests. If I understand correctly, metadata is
> fetched in separate queries as the instance object is
> created. Everything seems to work just fine, and I've considerably
> reduced the amount of data fetched from the database, as well as
> reduced the average response time of API requests.
>
> Given how simple it is and the results I'm getting, I don't see any
> reason not to patch my clusters with this change.
>
> Do you guys see any other impact this change could have? Anything that
> it could potentially break?

This is probably fine as a bandage fix, but it's not the right one for
upstream, IMHO. By doing what you did, you cause two RPC round-trips to
fetch the instance and then the metadata every single time the metadata
API is hit (not including the cache). By converting the DB load to do
the two-step, we still hit the DB twice, but only one RPC round-trip,
which will be much more efficient especially at load/scale.

--Dan