If you experience bad performance when running queries check the following:
There is one driver setting that may affect fetching the data and that is the fetch size driver property. In DbVisualizer do the following in the Connection Properties and the Driver Properties category.
Insert a new row in the grid (Parameter = Value) and specify:
java.sql.statement.setFetchSize = 500
Reconnect and verify. You may adjust the value until you get descent performance.