Re: Oracle 10g2 LIKE operator and case-insensitive issues

On May 11, 8:50 am, Steve Chien <stevech..._at_wisagetech.com> wrote:
> Hi,
>
> We're curerrently facing some performance issues related to the
> "LIKE" operator in Oracle 10g2. Here is what we encountered.
>
> We have a Oracle 10g2 database which has the following
> characteristics.
>
> NLS_CHARACTERSET => AL32UTF8
> NLS_NCHAR_CHARACTERSET => AL16UTF16
> NLS_RDBMS_VERSION => 10.2.0.1.0
>
> We created a table like below.
> -- creates test table
> CREATE TABLE MYTEST
> (id NUMBER(10, 0) NOT NULL,
> str1 VARCHAR2(128) NOT NULL,
> str2 NVARCHAR2(128) NOT NULL);
>
> Then, we populated with some random data.
> -- PL/SQL for creating random data
> BEGIN
> DBMS_RANDOM.SEED('thisisjustatest');
> FOR i IN 1 .. 100000 LOOP
> INSERT INTO MYTEST VALUES(i, DBMS_RANDOM.STRING('P', 64),
> DBMS_RANDOM.STRING('P', 64));
> END LOOP;
> INSERT INTO MYTEST VALUES(100001, 'steve', 'chien');
> INSERT INTO MYTEST VALUES(100002, 'STEVE', 'CHIEN');
> END;
>
> Afterwards, we created the indexes.
> -- creates indexes
> CREATE INDEX AK1_ID_MYTEST ON MYTEST(ID);
> CREATE INDEX AK2_STR1_MYTEST ON MYTEST(STR1);
> CREATE INDEX AK3_STR2_MYTEST ON MYTEST(STR2);
>
> With the "autotrace" turned on , NLS_COMP set to BINARY, and
> NLS_SORT set to BINARY in SQLPlus, we did two experiments.
>
> CASE I.
> select * from mytest where str1 = 'steve'
>
> Plan hash value: 587925449
>
> -----------------------------------------------------------------------------------------------
> | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
> -----------------------------------------------------------------------------------------------
> | 0 | SELECT STATEMENT | | 1 | 209 | 5 (0)| 00:00:01 |
> | 1 | TABLE ACCESS BY INDEX ROWID| MYTEST | 1 | 209 | 5 (0)| 00:00:01 |
> |* 2 | INDEX RANGE SCAN | AK2_STR1_MYTEST | 1 | | 3 (0)| 00:00:01 |
> -----------------------------------------------------------------------------------------------
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
>
> 2 - access("STR1"='steve')
>
> CASE II.
> select * from mytest where str1 like 'steve%';
>
> Plan hash value: 587925449
>
> -----------------------------------------------------------------------------------------------
> | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
> -----------------------------------------------------------------------------------------------
> | 0 | SELECT STATEMENT | | 1 | 209 | 5 (0)| 00:00:01 |
> | 1 | TABLE ACCESS BY INDEX ROWID| MYTEST | 1 | 209 | 5 (0)| 00:00:01 |
> |* 2 | INDEX RANGE SCAN | AK2_STR1_MYTEST | 1 | | 3 (0)| 00:00:01 |
> -----------------------------------------------------------------------------------------------
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
>
> 2 - access("STR1" LIKE 'steve')
>
> Here is what bothered us more... We actually wanted to do
> case-insensitive searches & sorts on columnes str1 & str2. We dropped
> the indexes and re-created them as blows.
>
> - drop & re-create indexes
> DROP INDEX AK1_ID_MYTEST;
> DROP INDEX AK2_STR1_MYTEST;
> DROP INDEX AK3_STR2_MYTEST;
>
> - creates indexes
> CREATE INDEX AK1_ID_MYTEST ON MYTEST(ID)
> CREATE INDEX AK2_STR1_MYTEST ON MYTEST(NLSSORT(STR1,
> 'NLS_SORT=GENERIC_M_CI'));
> CREATE INDEX AK3_STR2_MYTEST ON MYTEST(NLSSORT(STR2,
> 'NLS_SORT=GENERIC_M_CI'));
>
> With "autotrace" turned on, NLS_COMP set to LINGUISTIC, and NLS_SORT
> set to GENERIC_M_CI in SQLPlus, we dir the following two test cases.
>
> CASE I.
> select * from mytest where str1 = 'steve'
>
> Plan hash value: 3883648009
>
> ------ -
> -----------------------------------------
> | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
> ------ -
> -----------------------------------------
> | 0 | SELECT STATEMENT | | 851 | 173K| 404 (1)| 00:00:05 |
> | 1 | TABLE ACCESS BY INDEX ROWID| MYTEST | 851 | 173K| 404 (1)| 00:00:05 |
> |* 2 | INDEX RANGE SCAN | AK2_STR1_MYTEST | 340 | | 3 (0)| 00:00:01 |
> ------ -
> -----------------------------------------
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
>
> 2 - access(NLSSORT("STR1",'nls_sort=''GENERIC_M_CI''')=HEXTORAW('
> 024F025501FE026101FE00000202020202') )
>
> CASE II.
> select * from mytest where str1 like 'steve%';
>
> Plan hash value: 1692938441
>
> ------ - -----------------------------------------
> | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
> ------ - -----------------------------------------
> | 0 | SELECT STATEMENT | | 32 | 6688 | 791 (1)| 00:00:10 |
> |* 1 | TABLE ACCESS FULL| MYTEST | 32 | 6688 | 791 (1)| 00:00:10 |
> ------ - -----------------------------------------
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
>
> 1 - filter("STR1" LIKE 'steve%')
>
> Oracle was using the "TABLE ACCESS FULL" to handle the "LIKE"
> operator. It's extremely slow and we wondered why it couldn't use the
> "INDEX RANGE SCAN" anymore.
>
> Thanks for any suggestion!
>
> - Steve

On asktom.oracle.com you can find useful information about Oracle db case sensitive. However
from 10gR2 you can use
NLS_COMP = LINGUISTIC
NLS_SORT = BINARY_CI it make searches case insensitive

Bye
 Cristian Cudizio

http://oracledb.wordpress.com
http://cristiancudizio.wordpress.com Received on Fri May 11 2007 - 02:00:03 CDT