Later versions of hive have a "sys" DB that under the hood connects back to the hive metastore database (eg Postgres or whatever). and you can query that.
Impala seems not to be able to see this sys db though.
There is also a "information_schema" DB with a smaller and cleaner subset but it points back to sys and also not visible from impala if you do a "show databases;"
You can use "show" statements in impala-shell but I'm not sure there is a DB to through SQL at via ODBC/JDBC.
Still looking for a way to do this in impala