Question on optimum choice of index - whether to use CTXCAT or CONTEXT

Question

Hi ,
I have a situation in which there are short texts that are to be searched for diacritical characters and for that I implemented CTXCAT type of index. The solution works fine except for left side wild card search - in that case I have suggested the developers to use the query template feature. -this is the background information for the question I have and following example demonstrates it:
CREATE TABLE TEST_USER
  FIRST_NAME  VARCHAR2(64 CHAR)                 NOT NULL,
  LAST_NAME   VARCHAR2(64 CHAR)                 NOT NULL
CREATE INDEX TEST_USER_IDX3 ON TEST_USER
(FIRST_NAME)
INDEXTYPE IS CTXSYS.CTXCAT
PARAMETERS('LEXER cust_lexer');
CREATE INDEX TEST_USER_IDX4 ON TEST_USER
(LAST_NAME)
INDEXTYPE IS CTXSYS.CTXCAT
PARAMETERS('LEXER cust_lexer');
Don't worry about the cust_lexer, it is for diacritical search and it is not relevant to this question so I am not copying the code for the preference I created etc.
Now I have a row of data in the table with first_name column as Supervisor. If I run the below sql, it gives output:
SELECT *
  FROM test_user
WHERE catsearch (first_name, 'Supervisor', NULL) > 0;
FIRST_NAME                     LAST_NAME
Supervisor                     upervisor
--even the below sql with wild card (*) at the end works fine...
SQL> SELECT *
  2    FROM test_user
  3   WHERE catsearch (first_name, 'Super*', NULL) > 0;
FIRST_NAME                     LAST_NAME
Supervisor                     upervisor
However the below sql queries doesn't give any output, though they should return the same row as above!
SQL> SELECT *
  2    FROM test_user
  3   WHERE catsearch (first_name, '*visor', NULL) > 0;
no rows selected
SQL> SELECT *
  2    FROM test_user
  3   WHERE catsearch (first_name, '*vis*', NULL) > 0;
no rows selected
--Using query template as below solves the issue:
select * from test_user
where catsearch(first_name,
'<query>
  <textquery grammar="context">
     %viso%
  </textquery>
</query>','')>0
FIRST_NAME                     LAST_NAME
Supervisor                     upervisor
Note that I verified the query execution plan and it uses the index and there is no Full Table Scan:
| Id  | Operation                   | Name           | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT            |                |       |       |     9 (100)|          |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_USER      |   376 |    99K|     9   (0)| 00:00:01 |
|*  2 |   DOMAIN INDEX              | TEST_USER_IDX3 |       |       |            |          |
---------------------------------------------------------------------------------------------- Up to the above , all details were by way of the back ground...now the question is - it is this the right choice? I am using context grammer using query template. There is another thread on this forum where an expert (Barbara) said that
". It should be better to use a context index than a ctxcat index with a query template that uses context grammar. " -this was said on this question link: Re: Wildcard Search
So I am getting this doubt. However I have good data here that shows that the query doesn't do full table scan - still is it a bad choice? Note that there are several issues with CONTENT type of indexes( as per my limited understanding) - because they are not transactional in nature and so we have to take extra steps/measures to have the indexes updated which seems like a major pain area to me.
My doubt is , did I do the right thing by using query template or should I use the CONTEXT type of index instead of CTXCAT type of index?
Thanks,
Nirav
Edited by: orausern on Jan 17, 2013 1:40 AM
Edited by: orausern on Jan 17, 2013 1:43 AM

Answer 1

I would just like to add a few comments.
Alhough it is documented that the ctxcxat index and catsearch do not support a wildcard in front of the term, a workaround is to use two asterisks on the left side of the term, as demonstrated below. I provide this only for clarification and interesting trivia. I would still use a context index for various reasons.
SCOTT@orcl_11gR2> CREATE TABLE TEST_USER
  2    (FIRST_NAME  VARCHAR2(64 CHAR))
  3  /
Table created.
SCOTT@orcl_11gR2> INSERT INTO test_user VALUES ('Supervisor')
  2  /
1 row created.
SCOTT@orcl_11gR2> CREATE INDEX TEST_USER_IDX
  2  ON TEST_USER (FIRST_NAME)
  3  INDEXTYPE IS CTXSYS.CTXCAT
  4  /
Index created.
SCOTT@orcl_11gR2> SET AUTOTRACE ON EXPLAIN
SCOTT@orcl_11gR2> SELECT * FROM test_user
  2  WHERE  catsearch (first_name, '**vis*', NULL) > 0
  3  /
FIRST_NAME
Supervisor
1 row selected.
Execution Plan
Plan hash value: 4046491764
| Id  | Operation                   | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT            |               |     1 |   142 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST_USER     |     1 |   142 |     3   (0)| 00:00:01 |
|*  2 |   DOMAIN INDEX              | TEST_USER_IDX |       |       |            |          |
Predicate Information (identified by operation id):
   2 - access("CTXSYS"."CATSEARCH"("FIRST_NAME",'**vis*',NULL)>0)
Note
   - dynamic sampling used for this statement (level=2)
SCOTT@orcl_11gR2>The only time that I am aware of that there is a conflict between a wordlist and a lexer is when you specify stemming in both. If you are using stemming, you can still use both a wordlist and a lexer, but only set the stemmer attribute in the wordlist, not the index_stems attribute in the lexer.