Oracle 8.1.6, slow performance using XSU

Question

Hi,
We have a problem with some queries running in our production environment. When we run them directly through sqlplus they take milliseconds, however when we pass them through our wrapper to the XSU, they can take 5 or 6 seconds to return. The type of query just involves reading data from the database and returning it in XML through the XSU. The wrapper procedure we have written is shown below. Some of the XML we get back can be quite big, hence the check on the return length, but nothing greater than this length will normally be passed through the XSU. We have no issues with indexes etc, as I say the queries run fast if we don't process them through the XSU.
We beleive that the problems may be exaggerated by the load on the database at any time, and are going to investigate this further in the production environment when we get a chance but at the moment we are a bit stumped.
Does anyone have an idea why we are experiencing such large overheads when going through the XSU? Is there anything in our wrapper procedure which could add to the delay? Would introducing bind variables into our queries help? Any advice much appreciated.
PROCEDURE XML_Query(p_SQL IN VARCHAR2,
p_XML OUT LONG) IS
     v_Context          DBMS_XMLQuery.ctxType;
     v_CLOB      CLOB;
     v_Length          INTEGER;
     v_Buffer          VARCHAR2(2767);
     v_Amount          BINARY_INTEGER := 30000;
     v_Offset          INTEGER := 1;
     e_OutputTooLarge     EXCEPTION;
BEGIN
     --Get the query context
     v_Context := DBMS_XMLQuery.newContext(p_SQL);
     --v_Context := DBMS_XMLQuery.newContext('SELECT * FROM COLL_SCHEME');
     --Set the date format
     DBMS_XMLQuery.setDateFormat(v_Context,'dd/MM/yyyy hh:mm:ss');
     --Get the XML result
     v_CLOB := DBMS_XMLQuery.getXML(v_Context);
     --Check the length of the result
     v_Length := DBMS_LOB.GETLENGTH(v_CLOB);
     --We currently have a 32767 character limit
     IF v_Length > 32767 THEN
          --Close the context
          DBMS_XMLQuery.closeContext(v_Context);
          --Raise exception
          RAISE e_OutputTooLarge;
     END IF;
     --The first output is always the XML header <?xml version = '1.0'?>
     --We dont want it, so set the Offset to 24 to skip it
     v_Offset := 24;
     --Read the result into the output parameter (max 30000 chars at a time)
     DBMS_LOB.READ(v_CLOB,v_Amount,v_Offset,p_XML);
     --If there is more, get the remaining chars (up to another 2767)
     IF v_Length > 30000 THEN
          v_Amount := 2767;
          DBMS_LOB.READ(v_CLOB,v_Amount,30000,v_Buffer);
          p_XML := p_XML || v_Buffer;
     END IF;
     --Close the context
     DBMS_XMLQuery.closeContext(v_Context);
EXCEPTION
     WHEN e_OutputTooLarge THEN
          -- Raise the error to the calling process
          RAISE_APPLICATION_ERROR(-20000,'XML output to large. (' || TO_CHAR(v_Length) || ')');
END XML_Query;

Answer 1

Thanks Justin. I tried what you suggested. Here's the findings:
1. increase prefetch count -- did not seem to make a significant difference;
2. tried MicroSoft ODBC driver -- See to be a little quicker, but still way slower than native SQLnet or Net8;
3. Use Oracle ODBC test instead of application -- Oracle ODBC test seem to restrict the max row retrieval to 100 rows -- but it still take 10 to 20 seconds, which means for 800 rows it will take the same amount of time. I checked the NT taskmanager, while retieving data there's no CPU consumption.
4. Installed Oracle to another machine in the same location on NT/wintel box. Response time ODBC vs SQLnet is comparable (50 msec or so) on 200 rows data retrieval. The production database is in DEC alpha machine running NT.
Based on all these testing, I am still not sure what might have caused the performance problem in production oracle. Any further suggestions?
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