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CHAPTER 8 Transactions and Versioning
313
Hold cursors
Specifying the HOLD option when you open a cursor keeps the cursor open past
the end of the transaction, if the transaction ends in a
COMMIT. A hold cursor
does not remain open across a
ROLLBACK in which a cursor is opened.
Although the
HOLD option is not commonly used in a DSS environment, with
long transactions and no positioned updates, it may prove useful in some
situations. For example, many existing applications expect to use hold cursors,
and some ODBC drivers use hold cursors by default.
Adaptive Server IQ provides the version management needed for hold cursors.
Hold cursors do impact performance. All resources used by the cursor,
including memory, disk space, and process threads, are held until the cursor is
closed.
Positioned operations
In a positioned operation, the current location of the cursor determines where
a read or write operation begins. Adaptive Server IQ supports positioned
fetches, which can be helpful in long query transactions. It does not support
positioned updates, which are intended for shorter insertions and deletions. For
the most part, updates to IQ databases are likely to involve large amounts of
data; repositioning is a very minor part of such write operations.
Cursor command syntax and examples
For more information on using cursors in procedures, including examples of
cursor use, see Chapter 6, “Using Procedures and Batches”. For syntax of
cursor-related commands, see the Adaptive Server IQ Reference Manual.
Controlling message logging for cursors
By default, cursor operations are not logged in the IQ message file. If you need
to track cursor operations in order to determine the cause of a problem, turn on
the Log_Cursor_Operations option to produce a message each time a cursor is
opened or closed. See the Adaptive Server IQ Reference Manual for details.