Gunther Hagleitner, et al, walk us through some reasons why we might want to use Apache Hive for data virtualization:
Assume you want to execute a Hive query that accesses data from an external RDBMS behind a JDBC connection. A possible naïve way of doing this would treat the JDBC source as a “dumb” storage system, reading all the raw data over JDBC and processing it in Hive. In this case you would ignore the query capabilities of the RDBMS and pull too much data over the JDBC link, thus ending up with poor performance and an overloaded system.
For that reason, Hive implements smart push-down to other systems by relying on its storage handler interfaces and cost-based optimizer (CBO) powered by Apache Calcite. In particular, Calcite provides rules that match a subset of operators in the logical representation of the query and generates a new equivalent representation with more operations executed in the external system. Hive includes those rules that push computation to the external systems in its query planner, and then relies on Calcite to generate a valid query in the language that those systems support. The storage handler implementations are responsible to send the generated query to the external system, retrieve its results, and transform the incoming data into Hive internal representation so it can be processed further if needed.
A lot of platforms are moving toward data virtualization (e.g., SQL Server with its Big Data Clusters). That appears to be the next product battleground.