[openstack-dev] [nova] Metadata API cross joining "instance_metadata" and "instance_system_metadata"
dms at danplanet.com
Tue Oct 23 16:01:40 UTC 2018
> I tested a code change that essentially reverts
> 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.
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