This patch proposes a method for operators to customize the aggregation
query executed against Gnocchi. By default, we use the following query:
(aggregate RE_AGGREGATION_METHOD (metric METRIC_NAME AGGREGATION_METHOD))
Therefore, this option enables operators to take full advantage of
operations available in Gnocchi, such as any arithmetic operations,
logical operations and many others. When using a custom aggregation
query, one can use the placeholders `RE_AGGREGATION_METHOD`,
`AGGREGATION_METHOD`, and `METRIC_NAME`: they will be replaced at
runtime by values from the metric configuration.
Different use cases can be addressed with the use of custom queries such
as handling RadosGW usage data trimming, which causes a decrease in the
usage data values; Libvirt attach/detach of disks, migration of VMs,
start/stop of VMs, which will zero the usage data that are gathered by
Ceilometer compute, and many other use cases where one might desire a
more complex operation to be executed on the data before CloudKitty
rates it.
Change-Id: I3419075d6df165409cb1375ad11a5b3f7faa7471
bac1960330