[openstack-dev] [nova] Metadata API cross joining "instance_metadata" and "instance_system_metadata"

Dan Smith dms at danplanet.com
Mon Oct 22 18:01:37 UTC 2018

> Of course this is only a problem when instances have a lot of metadata
> records. An instance with 50 records in "instance_metadata" and 50
> records in "instance_system_metadata" will fetch 50 x 50 = 2,500 rows
> from the database. It's not difficult to see how this can escalate
> quickly. This can be a particularly significant problem in a HA
> scenario with multiple API nodes pulling data from multiple database
> nodes.

We haven't been doing this (intentionally) for quite some time, as we
query and fill metadata linearly:


and have since 2013 (Havana):


So unless there has been a regression that is leaking those columns back
into the join list, I'm not sure why the query you show would be

Just to be clear, you don't have any modifications to the code anywhere,
do you?


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