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Nova's got this REST API [1] which pulls task_log data from the nova 
database if the 'instance_usage_audit' config option value is True on 
any compute host.

That table is populated in a periodic task from all computes that have 
it enabled and by default it 'audits' instances created in the last 
month (the time window is adjustable via the 
'instance_get_active_by_window_joined' config option).

The periodic task also emits a 'compute.instance.exists' notification 
for each instance on that compute host which falls into the audit 
period. I'm fairly certain that notification is meant to be consumed by 
Ceilometer which is going to store it in it's own time-series database.

It just so happens that Nova is also storing this audit data in it's own 
database, and never cleaning it up - the only way in-tree to move that 
data out of the nova.task_log table is to archive it into shadow tables, 
but that doesn't cut down on the bloat in your database. That 
os-instance-usage-audit-log REST API is relying on the nova database though.

So my question is, is anyone using this in any shape or form, either via 
the Nova REST API or Ceilometer? Or are you using it in one form but not 
the other (maybe only via Ceilometer)? If you're using it, how are you 
controlling the table growth, i.e. are you deleting records over a 
certain age from the nova database using a cron job?

Mike Bayer was going to try and find some large production data sets to 
see how many of these records are in a big and busy production DB that's 
using this feature, but I'm also simply interested in how people use 
this, if it's useful at all, and if there is interest in somehow putting 
a limit on the data, i.e. we could add a config option to nova to only 
store records in the task_log table under a certain max age.

[1] 
http://developer.openstack.org/api-ref/compute/#server-usage-audit-log-os-instance-usage-audit-log

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Thanks,

Matt Riedemann