Pattern for sharing a large amount of data between the web application and a backend service in a Service Oriented Application

I have a web application which performs CRUD operations on a database. At times, I have to run a backend job to do a fair amount of number crunching/analytics on this data. This backend job will be written as a different service in a concurrent language, which will be independent of the main web application.

But actually sharing the DB between the 2 applications is probably not a best practice as it will lead to tight coupling. What is the right pattern to use here? Since this data might amount to millions of DB rows, I'm not sure using a message queue / REST APIs would be the best way to go.

This is perhaps a very common scenario and many companies/devs have already solved this problem. Any pointers will be helpful.