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[Jay Pipes <jaypipes@xxxxxxxxx>]

Hey all,

	A few deployers of Diablo, including Wikipedia, were experiencing very
slow response times from the EC2 metadata service in Nova. Yesterday and
today I tracked the bug down to a problem in the way the database
queries for the metadata results were being generated.

I'm not all that keen to submit the code to the stable/diablo branch --
for two reasons: I don't really want to spend the time to write test
cases for the code and Essex and beyond do NOT have this problem.

But, if you are experiencing very long response times from the metadata
service in a Diablo deployment, you can check out the patch that fixes
this issue here:

https://github.com/jaypipes/nova/commit/8becb58127ce7a10e81c68cba1ea5469db5b17d1

Ryan Lane at Wikipedia reports that the patch does indeed reduce
metadata response times for an individual guest -- such as when
cloud-init makes calls to the metadata service -- in his case from 11-15
seconds per call down to 0.1 second. Administrative calls to get
metadata for all instances also drops pretty dramatically, due to the
removal of now-unnecessary joins in the database queries in question.

Cheers,
-jay