Namespaced Query Time Lookups might not handle drivers correctly

[drcrallen]

As per https://groups.google.com/d/msg/druid-user/3Iqi6yYG5pA/MmWDZW0BBAAJ there might be a problem in the JDBCExtractionNamespaceFunctionFactory whereby the JDBC driver is not registered with the DBI. It is notable that MySQLConnector and PostgreSQLConnector have explicit registering of the driver in part of the constructor.

A few issues arise here:

1. The classloaders for the connector extensions are isolated from the namespaced lookup extension, this means that even if the proper registering were enforced, it is not guaranteed that the namespaced lookup extension would be using the registration from the mysql (or postgress) extension.
2. The connectors probably need more abstraction to allow non-metadata stuff to utilize them.
3. The JDBCExtractionNamespaceFunctionFactory would need a way to either A) pull from a extension config (assuming all lookups will use the same JDBC URI), or B) have a means to plug into an extension's JDBC driver registry so that different instances of namespaces can load up their drivers properly.
4. ClassLoader and JDBC driver dependencies are notoriously difficult to catch in unit tests.

[MdeArcayne]

So #2819 does not fix this yet? So far Its been impossible for me to use a JDBC lookup, same reason as the original group post. Has anyone succeeded in using them?

[b-slim]

Sorry @MdeArcayne #2819 will have the same driver issue.

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