If you need to make a tool(and use twice the amount of storage) to be able to "query your data" in a SQL manner while using noSQL, it probably means you are using the wrong tool for the job.
Actually, it is pretty common to replicate the transactional data into another data store for analytical purpose. However, using PostgreSQL as the OLAP data store may not be the wisest move.
Comments
If you need to make a tool(and use twice the amount of storage) to be able to "query your data" in a SQL manner while using noSQL, it probably means you are using the wrong tool for the job.
Actually, it is pretty common to replicate the transactional data into another data store for analytical purpose. However, using PostgreSQL as the OLAP data store may not be the wisest move.