Using PreparedStatement and the Oracle Error ORA-1000

Question

Hi,
I have a question about PreparedStatement objects that is not so simple to explain for me. What I would like to know is: if I use a PreparedStatement following traditional and generic steps:
1- PreparedStatement pStmt = Connection.prepareStatement(sQuery);
2- pStmt.setXXX(i,j);
n - pStmt.setXXX(i,j);
n+1 - ResultSet rs = pStmt.executeQuery();
n+2 - while(rs.next()){ ... retrive ResultSet data  ... }
n+3 - rs.close()
n+4 - back to point number 2
and at the end (as you can see in the point numbered n+4), instead of closing the PreparedStatement pStmt using the close() method, I reuse the PreparedStatement pStmt comeing back to the point numebr 2 and setting again all its parameters with new values ... then ... what heppens in the Oracle database ? Has been the cursor (so the mamory area), associated to my PreparedStatement object pStmt, duplicated or is it the same ?
I know that Java allows you to do this kind of operations with PreparedStatement, and I know that in tha Java Documentation is explained to follow this strategy to optimize the execution time because in this way the same PreparedStatement is precompiled and prepared only once. But if I do a for loop following the steps explained before, after many iterations I have the error "ORA-1000: maximum open cursors exceeded". This error is the reason of my question. Does this error means that it's mandatory to close a PreparedStatement always, otherwise if you reuse it without closing it then the corresponding database cursor will be duplicated ? If it is so, then I think this is a contradiction with official java documentation ...
I'm using Oracle8i (version 8.1.7) and Oracle JDBC Thin Driver (Windows NT) for use with JDK 1.2.x. Moreover, in my database istance the parameter "maximum open cursor" is equal to 800 ...
Thank you very much for suggestions :-)

Answer 1

There is no need to close a prepared statement or its resultset for every iteration.
After the first iteration in a loop, all subsequent executions of it will close the previous resultset. By adding close() method, you are making one extra costly call to the DB for no reason.
Following is the sample code.I know what you are saying. In fact at the beginning I wrote my code in the same way of your sample (see the code of my first post at the begin of this page).
But doing so, after thousand iterations of the loop, I had "Oracle Error ORA-1000 : maximun open cursor exeeded" even if in my database istance the parameter "maximum open cursor" is equal to 8000.
At this moment in my code, for each iteration, I close the PreparedStatement and in this way I don't have anymore the error :-((
So it seems that only in theory we can reuse a preparedStatement without closing it. In fact if we see the oracle system table "$open_cursor" (as Konrad Pietzka suggest me) we can find that, for each interation,
at our line code "rs = pstmt.executeQuery();" correspond a new cursor in the database: this means that for each method "pstmt.executeQuery()" the database open a new cursor and do not use the previous one as it should.
I posted a question two months ago to search if someone had the same problem (it seems that Konrad Pietzka had the same situation) and was able to explain me what is the cause.
The only reason I found by myself for this problem, is that probably the Oracle JDBC Thin Driver for Windows NT/2000 has some bugs... but I'm not sure ...
Thank you very much for you time !!
bye :-))
Fidalma