Performance issue with Oracle Text index

Question

Hi Experts,
We are on Oracle 11.2..0.3 on Solaris 10. I have implemented Oracle Text in our environment and I am facing a strange performance issue that is happening in our environment.
One sql having CONTAINS clause is taking forever - more than 20 minutes and still does not complete. This sql has a contains clause and an exists clause and a not exists clause.
Now if I remove the exists clause and a not exists clause , it completes fast. but with those two clauses it is just taking forever. It is late night so i am not able to post the table and sql query details and will do so tomorrow but based on this general description, are there any pointers for me to review?
sql query doing fine:
SELECT
    U.CLNT_OID, U.USR_OID, S.MAILADDR
FROM
    access_usr U
    INNER JOIN access_sia S
        ON S.USR_OID = U.USR_OID AND S.CLNT_OID = U.CLNT_OID
    WHERE U.CLNT_OID = 'ABCX32S'
    AND CONTAINS(LAST_NAME , 'TO%' ) >0
--sql query that hangs forever:
SELECT
    U.CLNT_OID, U.USR_OID, S.MAILADDR
FROM
    access_usr U
    INNER JOIN access_sia S
        ON S.USR_OID = U.USR_OID AND S.CLNT_OID = U.CLNT_OID
    WHERE U.CLNT_OID = 'ABCX32S'
    AND CONTAINS(LAST_NAME , 'TO%' ) >0
and exists (--one clause here wiht a few table joins)
and not exists (--one clause here wiht a few table joins);
--Now another strange thing I found is if instead of 'TO%' in this sql, if I were to use 'ZZ%' or 'L1%' it works fast but for 'TO%' it goes slow with those two exists not exists clauses!
I will be most thankful for the inputs.
OrauserN

Answer 1

Hi Barbara,
First of all, thanks a lot for reviewing the issue.
Unluckily making the change to empty_stoplist did not work out. I am today copying the entire sql here that has this issue and will be most thankful for more insights/pointers on what can be done.
Here is the entire sql:
SELECT U.CLNT_OID,
       U.USR_OID,
       S.EMAILADDRESS,
       U.FIRST_NAME,
       U.LAST_NAME,
       S.JOBCODE,
       S.LOCATION,
       S.DEPARTMENT,
       S.ASSOCIATEID,
       S.ENTERPRISECOMPANYCODE,
       S.EMPLOYEEID,
       S.PAYGROUP,
       S.PRODUCTLOCALE
  FROM    ACCESS_USR U
       INNER JOIN
          ACCESS_SIA S
       ON S.USR_OID = U.USR_OID AND S.CLNT_OID = U.CLNT_OID
WHERE     U.CLNT_OID = 'G39NY3D25942TXDA'
       AND EXISTS
              (SELECT 1
                 FROM ACCESS_USR_GROUP_XREF UGX
                      INNER JOIN ACCESS_GROUP RELG
                         ON     RELG.CLNT_OID = UGX.CLNT_OID
                            AND RELG.GROUP_OID = UGX.GROUP_OID
                      INNER JOIN ACCESS_GROUP G
                         ON     G.CLNT_OID = RELG.CLNT_OID
                            AND G.GROUP_TYPE_OID = RELG.GROUP_TYPE_OID
                WHERE     UGX.CLNT_OID = U.CLNT_OID
                      AND UGX.USR_OID = U.USR_OID
                      AND G.GROUP_OID = 920512943
                      AND UGX.INCLUDED = 1)
       AND NOT EXISTS
                  (SELECT 1
                     FROM    ACCESS_USR_GROUP_XREF UGX
                          INNER JOIN
                             ACCESS_GROUP G
                          ON     G.CLNT_OID = UGX.CLNT_OID
                             AND G.GROUP_OID = UGX.GROUP_OID
                    WHERE     UGX.CLNT_OID = U.CLNT_OID
                          AND UGX.USR_OID = U.USR_OID
                          AND G.GROUP_OID = 920512943
                          AND UGX.INCLUDED = 1)
       AND CONTAINS (U.LAST_NAME, 'Bon%') > 0;
Like I said before if the EXISTS and NOT EXISTS clause are removed it works in sub-second. But with those EXISTS and NOT EXISTS CLAUSE IT TAKES ANY WHERE FROM 25 minutes to more than one hour.
NOte also that it was not TO% but Bon% in the CONTAINS clause that is giving the issue - sorry that was wrong on my part.
Also please see below the ORACLE TEXT index defined on the table ACCESS_USER:
--definition of preferences used in the index:
SET SERVEROUTPUT ON size unlimited
WHENEVER SQLERROR EXIT SQL.SQLCODE
DECLARE
   v_err       VARCHAR2 (1000);
   v_sqlcode   NUMBER;
   v_count     NUMBER;
BEGIN
   ctxsys.ctx_ddl.create_preference ('cust_lexer', 'BASIC_LEXER');
   ctxsys.ctx_ddl.set_attribute ('cust_lexer', 'base_letter', 'YES'); -- removes diacritics
EXCEPTION
   WHEN OTHERS
   THEN
      v_err := SQLERRM;
      v_sqlcode := SQLCODE;
      v_count := INSTR (v_err, 'DRG-10701');
      IF v_count > 0
      THEN
         DBMS_OUTPUT.put_line (
            'The required preference named CUST_LEXER with BASIC LEXER is already set up');
      ELSE
         RAISE;
      END IF;
END;
DECLARE
   v_err       VARCHAR2 (1000);
   v_sqlcode   NUMBER;
   v_count     NUMBER;
BEGIN
   ctxsys.ctx_ddl.create_preference ('cust_wl', 'BASIC_WORDLIST');
   ctxsys.ctx_ddl.set_attribute ('cust_wl', 'SUBSTRING_INDEX', 'true'); -- to improve performance
EXCEPTION
   WHEN OTHERS
   THEN
      v_err := SQLERRM;
      v_sqlcode := SQLCODE;
      v_count := INSTR (v_err, 'DRG-10701');
      IF v_count > 0
      THEN
         DBMS_OUTPUT.put_line (
            'The required preference named CUST_WL with BASIC WORDLIST is already set up');
      ELSE
         RAISE;
      END IF;
END;
--now below is the code of the index:
CREATE INDEX ACCESS_USR_IDX3 ON ACCESS_USR
(FIRST_NAME)
INDEXTYPE IS CTXSYS.CONTEXT
PARAMETERS('LEXER cust_lexer WORDLIST cust_wl SYNC (ON COMMIT)');
CREATE INDEX ACCESS_USR_IDX4 ON ACCESS_USR
(LAST_NAME)
INDEXTYPE IS CTXSYS.CONTEXT
PARAMETERS('LEXER cust_lexer WORDLIST cust_wl SYNC (ON COMMIT)');
The strange thing is that, like I said, If I remove the exists clause the query returns very fast. Also if I modify the query to use only one NOT EXISTS clause and remove the other EXISTS clause it returns in less than one second.  Also if I remove the EXISTS clause and use only the NOT EXISTS  clause it returns in less than 4 seconds. But with both clauses it runs forever!
When I tried to get dbms_xplan.display_cursor to get the query plan (for the case of both exists and not exists clause in the query), it said that previous statement's sql id was 0 or something like that so that I was not able to see the query plan. I will keep trying to get this plan (it takes 25 minutes to one hour each time but will get this info soon). Again any pointers are most helpful.
Regards
OrauserN