Fetching and querying
Since m3query does not currently have a view into the M3DB index, fanout to multiple clusters is rather complicated. Since not every metric is necessarily in every cluster (as an example, carbon metrics routed to a certain resolution), it is not trivial to determine which namespaces should be queried to return a fully correct set of recorded metrics.
The general approach is therefore to attempt to fanout to any namespace which has a complete view of all metrics, for example,
Unaggregated, and take that if it fulfills the query range; if not, m3query will attempt to stitch together namespaces with longer retentions to try and build the most complete possible view of stored metrics.
For further details, please ask questions on our gitter, and we'll be happy to help!