Some Dimensions and Metrics are not retained that long, so you might need to run the collection more often than yearly to get the complete set of metrics you want.
I know other customers have run their REST queries automated/daily for "yesterday" to collect the full set of Metrics and Dimensions they want and used a custom script that was run yearly to concatenate the daily files into a single yearly archive and/or import the daily files into a separate SQL database as a set of bulk inserts.
Currently this is how I am using getDMIdata3 to get any data. is there a similar way to get historical data for each day in a year, using an API. Something like getting a memory dump?
If you want to create a long-term storage of DC RUM measurements outside DC RUM , I would recommend using the new API we have delivered in 12.4 for that purpose. Instead of hammering the system with REST API calls that invoke DB queries, the new API enables to access snapshots of selected data stored in the file system every monitoring interval. The required data is taken directly from DC RUM cache (without touching DB). We have create example Splunk application that uses this API: https://community.dynatrace.com/community/display/PUBDCRUM/Splunk+plugin+for+DC+RUM