US Patent 9471610 Scale-out of data that supports roll back

A computing resource monitoring service receives metrics data from customer applications and resources provided by a computing resource service provider. The metrics data is stored in observation journals within an observation journal logical data container. A map reduce processor is configured to obtain a current index file, the index file comprising a mapping of the metrics data stored within a metric store and a manifest comprising a listing of all processed observation journals. The map reduce processor may process the unprocessed observation journals to separate, sort and aggregate metrics data stored therein. This process generates index artifacts that may be merged with the index file, in an append-only process, to generate a new index file. An index pointer may be modified such that the map reduce processor refers to a different version of the index file in order to support roll back of metrics data.