The JDBC 4.0 specification supports three types of cursors: insensitive, sensitive, and forward-only asensitive. The SQL Anywhere JDBC driver is compliant with these JDBC specifications and supports these different cursor types for a JDBC ResultSet object. However, there are cases when the database server cannot construct an access plan with the required semantics for a given cursor type. In these cases, the database server either returns an error or substitutes a different cursor type.
With jConnect, the underlying protocol (TDS) only supports forward-only, read-only asensitive cursors on the database server, even though jConnect supports the APIs for creating different types of cursors following the JDBC 2.0 specification. All jConnect cursors are asensitive because the TDS protocol buffers the statement's result set in blocks. These blocks of buffered results are scrolled when the application needs to scroll through an insensitive or sensitive cursor type that supports scrollability. If the application scrolls backward past the beginning of the cached result set, the statement is re-executed, which can result in data inconsistencies if the data has been altered between statement executions.