* Avoids fetching all segment records into heap by JDBC driver
* Set connection to read-only to help database optimize queries
* Update JDBC drivers (MySQL has fixes for streaming results)
Geared towards supporting transactional inserts of new segments. This involves an
interface "DataSourceMetadata" that allows combining of partially specified metadata
(useful for partitioned ingestion).
DataSource metadata is stored in a new "dataSource" table.