Cursors
A cursor is a mechanism that points to one or more rows in a set of rows. The rows are retrieved from a table or in a result set that is returned by a stored procedure. Your application program can use a cursor to retrieve rows from a table.
About this task
Cursors bound with cursor stability that are used in block fetch operations are particularly vulnerable to reading data that has already changed. In a block fetch, database access prefetches rows ahead of the row retrieval controlled by the application. During that time the cursor might close, and the locks might be released, before the application receives the data. Thus, it is possible for the application to fetch a row of values that no longer exists, or to miss a recently inserted row. In many cases, that is acceptable; a case for which it is not acceptable is said to require data currency.
If your application requires data currency for a cursor, you need to prevent block fetching for the data to which it points. To prevent block fetching for a distributed cursor, declare the cursor with the FOR UPDATE clause.