JDBC Support

• The driver is not yet 100% complete. The Driver, Connection, Statement, PreparedStatement,
  and ResultSet implementations are reasonable, but the metadata calls are still in progress.
• You can access non-relational features of HBase not supported in JDBC,
  e.g., value versions and columns in the family default map, by casting a
  ResultSet to a ResulSetImpl and then calling ResultSetImpl.getCurrentHRecord().
• HBql supports both named parameters and parameters indicated with "?" character.
• JDBC examples can be seen here.
• Each connection makes use of an HTablePool. For a connection returned by
  Driver.getConnection(), the size of the HTablePool is specified in the jdbc url
  using the parameter maxtablerefs, e.g., "jdbc:hbql;maxtablerefs=10".
  For a connection pool, the size of the HTablePool is indicated with
  ConnectionPool.setMaxPoolReferencesPerTablePerConnection(10) prior to calling the ConnectionPool constructor.
• To create a non-pooled JDBC connection using a HBaseConfiguration object,
  you must call org.apache.hadoop.hbase.jdbc.Driver.getConnection(url, config).
• The JDBC connection url for HBase is "jdbc:hbql".
  There are two optional parameters: "maxtablerefs" and "hbase.master".