Yupp, you are right that disconnected Rowsets are not suitable for large datasets, but I'm not too sure about the second one. The following is a excerpt from the java.sun.com 's JDBC tutorial :
Rowsets may have many different implementations to fill different needs. These implementations fall into two broad categories, rowsets that are connected and those that are disconnected. A disconnected rowset gets a connection to a data source in order to fill itself with data or to propagate changes in data back to the data source, but most of the time it does not have a connection open. While it is disconnected, it does not need a JDBC driver or the full JDBC API, so its footprint is very small. Thus a rowset is an ideal format for sending data over a network to a thin client.
Because it is not continually connected to its data source, a disconnected rowset stores its data in memory. It needs to maintain metadata about the columns it contains and information about its internal state. It also needs a facility for making connections, for executing commands, and for reading and writing data to and from the data source. A connected rowset, by contrast, opens a connection and keeps it open for as long as the rowset is in use.
Although anyone can implement a rowset, most implementations will probably be provided by vendors offering RowSet classes designed for fairly specific purposes. To make writing an implementation easier, the Java Software division of Sun Microsystems, Inc., plans to provide reference implementations for three different styles of rowsets in the future. The following list of planned implementations gives you an idea of some of the possibilities.
A. A CachedRowSet class
—a disconnected rowset that caches its data in memory; not suitable for very large data sets, but an ideal way to provide thin Java clients, such as a Personal Digital Assistant (PDA) or Network Computer (NC), with tabular data
B. A JDBCRowSet class
—a connected rowset that serves mainly as a thin wrapper around a ResultSet object to make a JDBC driver look like a JavaBeans component
C. A WebRowSet class
—a connected rowset that uses the HTTP protocol internally to talk to a Java servlet that provides data access; used to make it possible for thin web clients to retrieve and possibly update a set of rows