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Held and non-held cursors

Posted on 2010-05-12 23:21 Prayer 阅读(175) 评论(0)  编辑 收藏 引用 所属分类: DB2

http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/index.jsp?topic=/com.ibm.db29.doc.apsg/db2z_heldnonheldcursor.htm

Held and non-held cursors

A held cursor does not close after a commit operation. A cursor that is not held closes after a commit operation. You specify whether you want a cursor to be held or not held by including or omitting the WITH HOLD clause when you declare the cursor.

After a commit operation, the position of a held cursor depends on its type:
  • A non-scrollable cursor that is held is positioned after the last retrieved row and before the next logical row. The next row can be returned from the result table with a FETCH NEXT statement.
  • A static scrollable cursor that is held is positioned on the last retrieved row. The last retrieved row can be returned from the result table with a FETCH CURRENT statement.
  • A dynamic scrollable cursor that is held is positioned after the last retrieved row and before the next logical row. The next row can be returned from the result table with a FETCH NEXT statement. DB2® returns SQLCODE +231 for a FETCH CURRENT statement.
A held cursor can close when:
  • You issue a CLOSE cursor, ROLLBACK, or CONNECT statement
  • You issue a CAF CLOSE function call or an RRSAF TERMINATE THREAD function call
  • The application program terminates.

If the program abnormally terminates, the cursor position is lost. To prepare for restart, your program must reposition the cursor.

The following restrictions apply to cursors that are declared WITH HOLD:
  • Do not use DECLARE CURSOR WITH HOLD with the new user signon from a DB2 attachment facility, because all open cursors are closed.
  • Do not declare a WITH HOLD cursor in a thread that might become inactive. If you do, its locks are held indefinitely.

IMS™

You cannot use DECLARE CURSOR...WITH HOLD in message processing programs (MPP) and message-driven batch message processing (BMP). Each message is a new user for DB2; whether or not you declare them using WITH HOLD, no cursors continue for new users. You can use WITH HOLD in non-message-driven BMP and DL/I batch programs.

CICS

In CICS® applications, you can use DECLARE CURSOR...WITH HOLD to indicate that a cursor should not close at a commit or sync point. However, SYNCPOINT ROLLBACK closes all cursors, and end-of-task (EOT) closes all cursors before DB2 reuses or terminates the thread. Because pseudo-conversational transactions usually have multiple EXEC CICS RETURN statements and thus span multiple EOTs, the scope of a held cursor is limited. Across EOTs, you must reopen and reposition a cursor declared WITH HOLD, as if you had not specified WITH HOLD.

You should always close cursors that you no longer need. If you let DB2 close a CICS attachment cursor, the cursor might not close until the CICS attachment facility reuses or terminates the thread.

The following cursor declaration causes the cursor to maintain its position in the DSN8910.EMP table after a commit point:

EXEC SQL
DECLARE EMPLUPDT CURSOR WITH HOLD FOR
SELECT EMPNO, LASTNAME, PHONENO, JOB, SALARY, WORKDEPT
FROM DSN8910.EMP
WHERE WORKDEPT < 'D11'
ORDER BY EMPNO
END-EXEC.

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