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Re: Performance diagnosis of metadata query


On 03/25/2012 01:03 PM, Justin Santa Barbara wrote:
The performance of the metadata query with cloud-init has been causing
some people problems (it's so slow cloud-init times out!), and has led
to the suggestion that we need lots of caching.  (My hypothesis is that
we don't...)

By turning on SQL debugging in SQL Alchemy (for which I've proposed a
patch for Essex: https://review.openstack.org/#change,5783), I was able
to capture the SQL statements.

I'm focusing on the SQL statements for the metadata call.

Is there a good way to map back where in the code these calls are coming from?

My install in nowhere near big enough for any of these to actually cause
a real problem, so I'd love to get timings / a log from someone that is
having a problem.  Even the table scan of fixed_ips should be OK if you
have enough RAM.

It's not just enough RAM, but that mysql was specifically tuned to have big table caches. Regardless, large table scans should be eliminated, especially if the table is mostly read, as the hit on an extra index on insert will be completely offset by the speedups on select.


Sean Dague
IBM Linux Technology Center
email: sldague@xxxxxxxxxx
alt-email: sdague@xxxxxxxxxxxxxxxxxx

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