Function Based Indexes - negative performance
Has anyone run across any cases where they have had issues with Function Based Indexes negatively impacting performance??
We are trying to use function based indexes in 9i (NLS_SORT=GENERIC_BASELETTER) and 10g (NLS_SORT=BINARY_CI) for case insensitivity.
We thought this was a decent solution until recently when testing with larger datasets. Any info is appreciated.
Thanks,
Just to clarify rreynoldson's first point:
All indexes will negatively impact inserts. Indexes, including function-based indexes, may or may not improve update and delete performance depending on whether the overhead of maintaining the index outweighs the benefit of being able to use the index to find the row(s) to update relatively quickly.
For user564260:
Assuming those parameters are set, make sure that you've gathered statistics on the function based index. If that doesn't resolve the problem, can you post a small test case that demonstrates the problem where you
- Create the table
- Create the indexes
- Populate it with data
- Run the query that you'd expect to use the FBI
- Post the explain plan
that would help us immensely.
Justin
Similar Messages
-
Function Based Index - Query Performance
HI,
Good Day to All..
I'd like to use function based indexes on following column(to_char(ps.user_pc_id)).
Whereas this column is part of PRIMARY KEY.
Is it possible to create a function based index on PRIMARY KEY Column?
Attached below is the query with the explain plan ...
TO_CHAR Expression - Performance
Thanks for your reply.DTYLER_APP@pssdev2> create table dt_fbi_pk(id varchar2(20));
Table created.
DTYLER_APP@pssdev2> drop table dt_fbi_pk;
Table dropped.
DTYLER_APP@pssdev2> create table dt_fbi(id number);
Table created.
DTYLER_APP@pssdev2> create index dt_fbi_idx on dt_fbi(to_char(id));
Index created.
DTYLER_APP@pssdev2> alter table dt_fbi add constraint dt_fbi_pk primary key (id);
Table altered.
DTYLER_APP@pssdev2> select constraint_name,constraint_type, index_name from user_constraints where table_name='DT_FBI';
CONSTRAINT_NAME C INDEX_NAME
DT_FBI_PK P DT_FBI_PK
1 row selected.When we created the primary key constraint, Oracle created a new index rather than using the existing one because....
DTYLER_APP@pssdev2> alter table dt_fbi drop primary key;
Table altered.
DTYLER_APP@pssdev2> select index_name from user_indexes where table_name ='DT_FBI';
INDEX_NAME
DT_FBI_IDX
1 row selected.
DTYLER_APP@pssdev2> alter table dt_fbi add constraint dt_fbi_pk primary key (id) using index dt_fbi_idx;
alter table dt_fbi add constraint dt_fbi_pk primary key (id) using index dt_fbi_idx
ERROR at line 1:
ORA-14196: Specified index cannot be used to enforce the constraint.
DTYLER_APP@pssdev2> alter table dt_fbi add constraint dt_fbi_uk unique(id) using index dt_fbi_idx;
alter table dt_fbi add constraint dt_fbi_uk unique(id) using index dt_fbi_idx
ERROR at line 1:
ORA-14196: Specified index cannot be used to enforce the constraint.We can't use a function based index to enforce a unique or primary key constraint. Changing the syntax does not help..
DTYLER_APP@pssdev2> alter table dt_fbi add constraint dt_fbi_uk unique(TO_CHAR(id)) using index dt_fbi_idx;
alter table dt_fbi add constraint dt_fbi_uk unique(TO_CHAR(id)) using index dt_fbi_idx
ERROR at line 1:
ORA-00904: : invalid identifierWe can create a unique index however
DTYLER_APP@pssdev2> drop index dt_fbi_idx;
Index dropped.
DTYLER_APP@pssdev2> create unique index dt_fbi_idx on dt_fbi(to_char(id));
Index created.but we still can't use it to enforce a unique or primary key constraint
DTYLER_APP@pssdev2> alter table dt_fbi add constraint dt_fbi_pk primary key (id) using index dt_fbi_idx;
alter table dt_fbi add constraint dt_fbi_pk primary key (id) using index dt_fbi_idx
ERROR at line 1:
ORA-14196: Specified index cannot be used to enforce the constraint.
DTYLER_APP@pssdev2> alter table dt_fbi add constraint dt_fbi_uk unique(id) using index dt_fbi_idx;
alter table dt_fbi add constraint dt_fbi_uk unique(id) using index dt_fbi_idx
ERROR at line 1:
ORA-14196: Specified index cannot be used to enforce the constraint.So no, you can't use it for a primary key. If you just want to enforce uniqueness then yes, you can do it with a unique index, but not a constraint.
DTYLER_APP@pssdev2> select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
5 rows selected.HTH
Daviid -
Performance problem on function-based index
Hi guys,
I am having performance problems with the addition of new function-based indexes.
alter session set nls_comp='ANSI';
alter session set nls_sort='BINARY_CI';
* have to run this because the of case-insensitivity requirements
I have a view. for ex:
create or replace view view1
as
select * from emp1,user
where emp1.empno=user.empno
union
select * from emp2,user
where emp2.empno=user.empno
union
select * from emp3,user
where emp3.empno=user.empno and so on
When I run this it works with a full table scan. Then when i created a function-based index:
create index user_ix on
user(nlssort(empno,'NLS_SORT=BINARY_CI'));
analyze index user_ix compute statistics;
analyze table user compute statistics;
the view hangs. but when i run the individual select statements it works.
Do you guys have any idea on what's going on? Any advise is greatly appreciated.
Thanks.LC is absolutely right. Brain cramp on my part.
On the other hand, I can't seem to coerce Oracle to apply a to_binary_double conversion as part of an implicit conversion.
var bin_dbl binary_double;
select to_binary_double(14) into :bin_dbl from dual;
SCOTT @ nx102 JCAVE9420> select * from emp where empno = :bin_dbl;
no rows selected
Elapsed: 00:00:00.14
Execution Plan
Plan hash value: 2949544139
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 39 | 1 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 39 | 1 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 0 (0)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access("EMPNO"=TO_NUMBER(:BIN_DBL))I'd expect that Oracle would try to convert the binary double to a number, not the other way around.
Justin -
Creation of function based index using escape
Hello,
I have the following SQL, sometimes performing bad:
SELECT DISTINCT UPPER(A.PROCESSIDCODE), UPPER(A.RULENAME), CHARSET
FROM XIB_DETECT A, XIB_PROCESSIDPROPERTIES B, XIB_RULES C
WHERE ( A.KEY1 = :P1 OR ( :P1 like REPLACE(REPLACE(REPLACE(REPLACE(KEY1,'%', '\%'),'_', '\_'),'?', '_'),'*','%') escape '\' AND A.REGFLAGS1 = 'Y') OR A.KEY1 = '*' AND A.REGFLAGS1 = 'Y')
AND (A.KEY2 = :P2 OR ( :P2 like REPLACE(REPLACE(REPLACE(REPLACE(KEY2,'%', '\%'),'_', '\_'),'?', '_'),'*','%') escape '\' AND A.REGFLAGS2 = 'Y') OR (A.KEY2 IS NULL AND A.REGFLAGS2 IS NULL ) )
AND (A.KEY3 = :P3 OR ( :P3 like REPLACE(REPLACE(REPLACE(REPLACE(KEY3,'%', '\%'),'_', '\_'),'?', '_'),'*','%') escape '\' AND A.REGFLAGS3 = 'Y') OR (A.KEY3 IS NULL AND A.REGFLAGS3 IS NULL ) )
AND (A.KEY4 = :P4 OR ( :P4 like REPLACE(REPLACE(REPLACE(REPLACE(KEY4,'%', '\%'),'_', '\_'),'?', '_'),'*','%') escape '\' AND A.REGFLAGS4 = 'Y') OR (A.KEY4 IS NULL AND A.REGFLAGS4 IS NULL ) )
AND (A.KEY5 = :P5 OR ( :P5 like REPLACE(REPLACE(REPLACE(REPLACE(KEY5,'%', '\%'),'_', '\_'),'?', '_'),'*','%') escape '\' AND A.REGFLAGS5 = 'Y') OR (A.KEY5 IS NULL AND A.REGFLAGS5 IS NULL ) )
AND (A.KEY6 IS NULL OR A.KEY6 = '*' AND REGFLAGS6 = 'Y')
AND (A.KEY7 IS NULL OR A.KEY7 = '*' AND REGFLAGS7 = 'Y')
AND (A.KEY8 IS NULL OR A.KEY8 = '*' AND REGFLAGS8 = 'Y')
AND (A.KEY9 IS NULL OR A.KEY9 = '*' AND REGFLAGS9 = 'Y')
AND (A.KEY10 IS NULL OR A.KEY10 = '*' AND REGFLAGS10 = 'Y')
AND ( ( A.PROCESSIDCODE IS NOT NULL AND UPPER(A.PROCESSIDCODE) = UPPER(B.PROCESSIDCODE) AND A.XLEVEL = B.XLEVEL AND B.ACTIVEFLAG = 'Y' )
OR ( A.RULENAME IS NOT NULL AND UPPER(A.RULENAME) = UPPER(C.RULENAME) AND A.XLEVEL = C.XLEVEL AND C.ACTIVEFLAG = 'Y' ) );
Now I want to create a function based index on the key1 column:
CREATE INDEX xib_detect_ix ON xib_detect (REPLACE(REPLACE(REPLACE(REPLACE(KEY1,'%', '\%'),'_', '\_'),'?', '_'),'*','%') escape '\') TABLESPACE ... ONLINE;
However, this is not working with "escape" '\', throwing: ORA-00907: missing right parenthesis
Any idea how to create an index on this construct with "escape"?
Database version is 10.2.0.3.
Thanks a lot.
Regards
OliverHi,
You can get the "missing right parenthesis" error for many different syntax errors.
In this case, you really are missing a right parenthesis. Your statement has 5 left '('s, but only 4 right ')'s. It's easy to see this if you format your code:
CREATE INDEX xib_detect_ix
ON xib_detect ( REPLACE ( REPLACE ( REPLACE ( REPLACE ( KEY1
escape '\'
ESCAPE is an option that you can use with the LIKE operator. It gives you a mechanism for cancelling the special meaning of symbols like '%'. You're not using the LIKE operator to create the index. You're only using REPLACE, and no characters have any special meaning in REPLACE, so there's no way (or reason) to escape them. Use ESCAPE in queries that use LIKE, when appropriate. -
FUNCTION-BASED INDEX ( ORACLE 8I NEW FEATURE )
제품 : ORACLE SERVER
작성날짜 : 2004-08-16
FUNCTION-BASED INDEX ( ORACLE 8I NEW FEATURE )
==============================================
SCOPE
10g Standard Edition(10.1.0) 이상 부터 Function-based Index 기능이 지원된다.
Explanation
1. 개요
Function-based index는, 함수(function)이나 수식(expression)으로 계산
된 결과에 대해 인덱스를 생성하여 사용할 수 있는 기능을 제공한다.
질의 수행 시 해당 함수나 수식을 처리하여 결과를 가져 오는 것이 아니라,
인덱스 형태로 존재하는 미리 계산되어 있는 결과를 가지고 처리하므로
성능 향상을 기할 수 있다.
2. 제약사항
1) aggregate function 에 대한 function-based index 생성 불가.
(예 : sum(...) )
2) LOB, REF, nested table 컬럼에 대한 function-based index 생성 불가.
3. 주요 특징
1) cost-based optimizer에 의해 사용됨.
2) B*Tree / bitmap index로 생성 가능.
3) 산술식 (arithmetic expression), PLSQL function, SQL built-in
function 등에 적용 가능.
4) 함수나 수식으로 처리된 결과에 대한 range scan 가능
5) NLS SORT 지원
6) SELECT/DELETE를 할 때마다 함수나 수식의 결과를 계산하는 것이 아니라
INSERT/UPDATE 시 계산된 값을 인덱스에 저장.
7) 질의 속도 향상
8) object column이나 REF column에 대해서는 해당 object에 정의된
method에 대해 function-based index 생성 가능.
4. 생성 방법
CREATE [UNIQUE | BITMAP ] INDEX <index_name>
ON <tablename> (<index-expression-list>)
<index-expression-list> -> { <column_name> | <column_expression> }
예) CREATE INDEX EMP_NAME_INDEX ON EMP (UPPER(ENAME));
CREATE INDEX EMP_SAL_INDEX ON EMP( SAL + COMM, empno);
* Function-based index를 생성하기 위해서는 QUERY REWRITE 권한이
부여 되어 있어야만 한다.
예) GRANT QUERY REWRITE TO SCOTT;
5. Function-Based Index 사용을 위한 사전 작업
1) Function-based index는 cost based optimizer에서만 사용 가능하므로,
테이블에 대해 미리 analyze 해 주는 것이 바람직하다.
그리고 init 파일에서 OPTIMIZER_MODE 를 FIRST_ROWS 나 ALL_ROWS 등으
로 지정하거나 HINT 등을 사용하여 cost based optimizer가 사용되도록
한다.
2) init 파일에서 COMPATIBLE 파라미터 값을 8.1 이상으로 설정되어 있어야
한다.
( 예 : COMPATIBLE = 8.1.6 )
3) session/instance level 에서 QUERY_REWRITE_ENABLED 값이 TRUE 지정
되어 있어야 한다.
( 예 : ALTER SESSION SET QUERY_REWRITE_ENABLED = TRUE; )
6. 예제
1) init 파라미터에서 다음과 같이 지정
compatible = 8.1.6 (반드시 8.1이상이어야 한다)
query_rewrite_enabled = true
query_rewrite_integrity = trusted
2) SCOTT 유저에서 function_based_index 생성
create index idx_emp_lower_ename
on emp
( lower(ename) ) ;
3) EMP table analyze
analyze table emp compute statistics ;
4) PLAN_TABLE 생성
@ ?/rdbms/admin/utlxplan.sql
5) Cost based optimizer 선택
alter session set optimizer_mode = FIRST_ROWS ;
6) Query 실행
explain plan set statement_id='qry1' FOR
select empno, ename
from emp
where lower(ename) = 'ford' ;
7) PLAN 분석
SELECT LPAD(' ',2*level-2)||operation||' '||options||' '||object_name query_plan
FROM plan_table
WHERE statement_id='qry1'
CONNECT BY prior id = parent_id
START WITH id = 0 order by id ;
-> 결과
QUERY_PLAN
SELECT STATEMENT
TABLE ACCESS BY INDEX ROWID EMP
INDEX RANGE SCAN IDX_EMP_LOWER_ENAME
7. 결론
Function-based index는 적절하게 사용될 경우 성능상의 많은 이점을 가져
온다. Oracle8i Designing and Tuning for Performance에서도 가능한 한
Function-based index를 사용하는 것을 권장하고 있으며, LOWER(), UPPER()
등의 함수를 사용하여 불가피하게 FULL TABLE SCAN을 하는 경우에 대해서도
효과적으로 처리해 줄 수 있는 방안이라 할 수 있다.
Reference Documents
-------------------Partha:
From the Oracle8i Administrators Guide:
"Table owners should have EXECUTE privileges on the functions used in function-based indexes.
For the creation of a function-based index in your own schema, you must be
granted the CREATE INDEX and QUERY REWRITE system privileges. To create
the index in another schema or on another schemas tables, you must have the
CREATE ANY INDEX and GLOBAL QUERY REWRITE privileges."
Hope this helps.
Peter -
Function-based Index and an OR-condition in the WHERE-clause
We have some problems with functin-based indexes and
the or-condition in a where-clause.
(We use oracle 8i (8.1.7))
create table TPERSON(ID number(10),NAME varchar2(20),...);
create index I_NORMAL_TPERSON_NAME on TPERSON(NAME);
create index I_FUNCTION_TPERSON_NAME on TPERSON(UPPER(NAME));
The following two statements run very fast on a large table
and the execution-plan asure the usage of the indexes
(-while the session is appropriate configured and the table is analyzed):
1) select count(ID) FROM TPERSON where upper(NAME) like 'MIL%';
2) select count(ID) from TPERSON where NAME like 'Mil%' or (3=5);
In particular we see that a normal index is used while the where-clause contains
an OR-CONDITION.
But if we try the similarly select-statement
3) select count(ID) FROM TPERSON where upper(NAME) like 'MIL%' or (3=5);
the CBO will not use the function-index.
(This behavior we only expect with views but not with indexes.)
We ask for an advice like an hint, which enable the CBO-usage
of function-based indexes in connection with OR.
This problem seems to be artificial because it contains this dummy logic:
or (3=5).
This steams from an prepared statement, where this kind of boolean
flag reduce the amount of different select-statements needed for
covering the hole business-logic, while using bind-variables for the
concrete query-parameters.
A more realistic (still boild down) version of our prepared select-statement run in
SQL Plus:
define x_name = 'MIL%';
define x_firstname = '';
select * FROM TPERSON
where (upper(NAME) like '&x_name' or ( '&x_name' = ''))
and (upper(FIRSTNAME) like '&x_firstname' or ('&x_firstname' = ''))
and ...;
In particular we dont refernce the tablecolumn , but the QUERY-Parameter
yield the second boolean value in the or-condition.
The problem is that this condition ('&x_name' = '') dont use any index.
thanks a lot for spending your time with this problemTry
SELECT /*+ RULE */
as your hint. I don't have the book with me, but this last weekend I read a section about your very problem. The book was a Oracle Press gold cover about Oracle 8i Performance tuning. If you e-mail me I can quote you the chapter when I get home Friday. -
Function Based Index on Date Column
Hi All,
I need to execute a query like this :
SELECT * FROM ORDERS WHERE APPROVE_DATE IS NULL
I read anywhere that this will cause unnecessary FTS so that I should create function based index.
I have tried one below , but not sure that this is correct approach :
CREATE INDEX idx_1
ON ORDERS (NVL(APPROVE_DATE, '01-JAN-1900'));
SELECT * FROM ORDERS WHERE NVL(APPROVE_DATE, '01-JAN-1900') = '01-JAN-1900'
Is this a correct approach ?
Thank you,
xtantoA SQL_TRACE output will explain clearly what Justin has stated.
I have created a table T based on all_objects.
SQL> desc t
Name Null? Type
OWNER NOT NULL VARCHAR2(30)
OBJECT_NAME NOT NULL VARCHAR2(30)
SUBOBJECT_NAME VARCHAR2(30)
OBJECT_ID NOT NULL NUMBER
DATA_OBJECT_ID NUMBER
OBJECT_TYPE VARCHAR2(19)
CREATED DATE
LAST_DDL_TIME NOT NULL DATE
TIMESTAMP VARCHAR2(19)
STATUS VARCHAR2(7)
TEMPORARY VARCHAR2(1)
GENERATED VARCHAR2(1)
SECONDARY VARCHAR2(1)
CASE I_
SQL> select count(1) from t
2 /
COUNT(1)
934320
SQL> select count(1) from t where created is null
2 /
COUNT(1)
2376The number of null values in CREATED column is proportionately very small.
Now i execute the query without function based index.
select *
from t
where created is null
call count cpu elapsed disk query current rows
Parse 1 0.00 0.09 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 160 0.04 0.10 0 12662 0 2376
total 162 0.04 0.19 0 12662 0 2376
Rows Execution Plan
0 SELECT STATEMENT GOAL: ALL_ROWS
2376 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'T' (TABLE)And here is the query that uses the function based index
select *
from t
where nvl(created,to_date('01-01-1900','DD-MM-YYYY')) = to_date('01-01-1900','DD-MM-YYYY')
call count cpu elapsed disk query current rows
Parse 1 0.01 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 160 0.01 0.01 0 698 0 2376
total 162 0.03 0.01 0 698 0 2376
Rows Execution Plan
0 SELECT STATEMENT GOAL: ALL_ROWS
2376 TABLE ACCESS GOAL: ANALYZED (BY INDEX ROWID) OF 'T' (TABLE)
2376 INDEX GOAL: ANALYZED (RANGE SCAN) OF 'T_FN_IDX' (INDEX)Its very obvious from the above output that the Function Based Index as increased the performance.
CASE II_
SQL> select count(1) from t
2 /
COUNT(1)
934320
SQL> select count(1) from t where created is null
2 /
COUNT(1)
202168Now the null values in the CREATED column is proportionately large than the first test case.
Now lets see without using the function based index
select *
from t
where created is null
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 13479 0.46 0.71 2 25832 0 202168
total 13481 0.46 0.71 2 25832 0 202168
Rows Execution Plan
0 SELECT STATEMENT GOAL: ALL_ROWS
202168 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'T' (TABLE)Now iam trying to use the function based index
select *
from t
where nvl(created,to_date('01-01-1900','DD-MM-YYYY')) = to_date('01-01-1900','DD-MM-YYYY')
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 13479 0.54 0.84 0 33826 0 202168
total 13481 0.54 0.84 0 33826 0 202168
Rows Execution Plan
0 SELECT STATEMENT GOAL: ALL_ROWS
202168 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'T' (TABLE)Its obvious from the result that oracle has decided to go for a FULL TABLE SCAN even when an index was available.
So just having a function based index is not going to increase the query performance. There are lot of other factors to be considered as stated above.
Thanks,
Karthick. -
Function Based index getting disabled frequently
I am facing some error like “ORA-30554: function-based index ORADB1.FUN_INDX1 is disabled” in the development database. I verified that the function which is referred by the index is valid. Once I even got the tedious generic error ORA-600 because of this. I referred the metalink and advised to drop and recreate the index
Dropping and recreating the index will solve the issue for 2-3 days and again the same will be repeated. So what I did is made the index unusable as it will not affect the other application activities. Can anybody give a clue on this issue?I am facing some error like “ORA-30554:
function-based index ORADB1.FUN_INDX1 is disabled” Cause: An attempt was made to access a function-based index that has been marked disabled because the function on which the index depends has been changed.
Action: Perform one of the following actions: -- drop the specified index using the DROP INDEX command -- rebuild the specified index using the ALTER INDEX REBUILD command -- enable the specified index using the ALTER INDEX ENABLE command -- make the specified index usable using the ALTER INDEX UNUSABLE command -
Query Transformation in Function Based Index's Expression
Hi All,
I am having a wired issue with Function Based Indexes on Orcale 10.2.0.3 running on Solaris 5.9.
I have created two FBI on two tables using following syntax.
CREATE INDEX EQHUB.IDX_BBO_WRT_DES_FBI ON EQHUB.BBO_WARRANT_PRICING (CASE WHEN latest_version_flag = 'Y' THEN 1 ELSE NULL END);
CREATE INDEX EQHUB.IDX_BBO_DES_FBI ON EQHUB.BBO_DESCRIPTIVE_DATA (CASE WHEN latest_version_flag = 'Y' THEN 1 ELSE NULL END);
For the second command (IDX_BBO_DES_FBI), when i query DBA_IND_EXPRESSIONS view, i found that Oracle has done some kind of QUERY TRANSFORMATION (?) and converted
FBI expression to CASE "LATEST_VERSION_FLAG" WHEN 'Y' THEN 1 ELSE NULL END.At the same time,EXPRESSION on first index is not changed.
Now,my question is what has made transformation to occure only for second index.
I also found that inspite of highly SELECTIVE nature of both the indexes, only SECOND index is being used by CBO (for which trasnformation occured)
and IDX_BBO_WRT_DES_FBI is not being used(FTS is happening instead).
Query is using same expression for both the tables as
(CASE WHEN latest_version_flag = 'Y' THEN 1 ELSE NULL END)=1
INDEX_NAME TABLE_NAME COLUMN_EXPRESSION
IDX_BBO_WRT_DES_FBI BBO_WARRANT_PRICING CASE WHEN "LATEST_VERSION_FLAG"='Y' THEN 1 ELSE NULL END
IDX_BBO_DES_FBI BBO_DESCRIPTIVE_DATA CASE "LATEST_VERSION_FLAG" WHEN 'Y' THEN 1 ELSE NULL ENDI read that expression should be evaluated including CASE of characters and spaces in query.Is that true?
Appreciating responses in advance.Randolf.
It's a shame that I forgot to look into the full execution plan information to check how Oracle really handles my queries.
Look here(edited for clarity):
explain plan for
select /*+ case1 ordered use_nl(x, y) */ count(case c1
when '1' then 1
when '2' then 2
when '3' then 3
else 4
end) from
(select level from dual connect by level <= 300000) x,
(select
from t1
) y;
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 2 | 5 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 2 | | |
| 2 | NESTED LOOPS | | 3 | 6 | 5 (0)| 00:00:01 |
| 3 | VIEW | | 1 | | 2 (0)| 00:00:01 |
| 4 | CONNECT BY WITHOUT FILTERING| | | | | |
| 5 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
| 6 | TABLE ACCESS FULL | T1 | 3 | 6 | 3 (0)| 00:00:01 |
Column Projection Information (identified by operation id):
1 - (#keys=0) COUNT(CASE WHEN "T1"."C1"='1' THEN 1 WHEN "T1"."C1"='2' THEN
2 WHEN "T1"."C1"='3' THEN 3 ELSE 4 END )[22]
2 - (#keys=0) "T1"."C1"[CHARACTER,1]
4 - "DUAL".ROWID[ROWID,10], LEVEL[4]
5 - "DUAL".ROWID[ROWID,10]
6 - "T1"."C1"[CHARACTER,1]
32 rows selected.
explain plan for select /*+ case2 ordered use_nl(x, y) */ count(case
when c1 = '1' then 1
when c1 = '2' then 2
when c1 = '3' then 3
else 4
end) from
(select level from dual connect by level <= 300000) x,
(select
from t1
) y;
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 2 | 5 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 2 | | |
| 2 | NESTED LOOPS | | 3 | 6 | 5 (0)| 00:00:01 |
| 3 | VIEW | | 1 | | 2 (0)| 00:00:01 |
| 4 | CONNECT BY WITHOUT FILTERING| | | | | |
| 5 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
| 6 | TABLE ACCESS FULL | T1 | 3 | 6 | 3 (0)| 00:00:01 |
Column Projection Information (identified by operation id):
1 - (#keys=0) COUNT(CASE WHEN "T1"."C1"='1' THEN 1 WHEN "T1"."C1"='2' THEN
2 WHEN "T1"."C1"='3' THEN 3 ELSE 4 END )[22]
2 - (#keys=0) "T1"."C1"[CHARACTER,1]
4 - "DUAL".ROWID[ROWID,10], LEVEL[4]
5 - "DUAL".ROWID[ROWID,10]
6 - "T1"."C1"[CHARACTER,1]As you exactly mentioned, I was executing different SQL but actually same queries!
Thanks for pointing my flaws.
PS) OP, forgive me for bothering you with off-topic things. :)
================================
Dion Cho - Oracle Performance Storyteller
http://dioncho.wordpress.com (english)
http://ukja.tistory.com (korean)
================================
Edited by: Dion_Cho on Feb 10, 2009 5:45 AM
Typo -
Impdp not importing function based index correctly.
We noticed that a process running in our develop database was running much faster than in the production database. After investigating we found that on the development database the process was using an index on the main large table and on the production database the index was ignored and full table scans of the large table were being used.
The data in the tables was the same, statistics were up-to-date, etc. Looking closer we saw that the index on the production database was function based because it had the DESC keyword on one column in the index. On the development database all columns of the index were ASC and thus it was a "normal" index. This was very confusing since we had just refreshed the development database from production using expdp/impdp. I ran impdp with the sqlfiles option to capture the DDL from the export file for the index in question from the production database:
CREATE UNIQUE INDEX "SYSADM"."PS_SF_1098_ITEM" ON "SYSADM"."PS_SF_1098_ITEM" ("EMPLID", "SF_TIN", "CALENDAR_YEAR", "SEQ_NO" DESC, "DTL_SEQ_NBR")
PCTFREE 10 INITRANS 2 MAXTRANS 255
STORAGE(INITIAL 40960 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
TABLESPACE "PSINDEX" ;
I then dropped the table/index in the development database and reimported just this one table. Sure enough, the index wasn't created as a function based index (no DESC keyword on SEQ_NO column):
CREATE UNIQUE INDEX "SYSADM"."PS_SF_1098_ITEM" ON "SYSADM"."PS_SF_1098_ITEM" ("EMPLID", "SF_TIN", "CALENDAR_YEAR", "SEQ_NO", "DTL_SEQ_NBR")
PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
STORAGE(INITIAL 40960 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
TABLESPACE "PSINDEX" ;
I've researched this extensively and can't find any information on why this is happening. Any ideas before I open a SR?
BTW.... version is 11.1.0.7 patchset 31 on Windows Server 2003. Both dev and prod environments are identical.
Thanks,
DanWorking on something else I noticed the following two "hidden" init.ora parameters in both my dev and production databases:
*._disable_function_based_index=TRUE
*._ignore_desc_in_index=TRUE
The first parameter explains why the index (function based) was being ignored in my production database. The second explains why the index is created without the DESC keyword in my dev database from an export from my prod database. I guess you do learn something new every day :)
These databases are used by Peoplesoft applications and I found several posts saying that function based indexes created by Peoplesoft were causing performance and/or data validity problems and users were instructed to set the above parameters so the FIB's weren't used. So, everything is working as expected/designed. I will contact Peoplesoft Tech Support to see if users are still encouraged to set the above parameters.
Dan -
Function based indexes on object tables
Hi,
I am trying to create a function based index on an object table. I am getting the following error:
SQL> create index cell1_indx on cell1(create_cell1(id)) indextype is mdsys.spatial_index;
create index cell1_indx on cell1(create_cell1(id)) indextype is mdsys.spatial_index
ERROR at line 1:
ORA-29855: error occurred in the execution of ODCIINDEXCREATE routine
ORA-13249: internal error in Spatial index: [mdidxrbd]
ORA-13249: Error in Spatial index: index build failed
ORA-13249: Stmt-Execute Failure: SELECT num_rows from all_tables where owner='ASHE' and table_name=
'CELL1'
ORA-06512: at "MDSYS.SDO_INDEX_METHOD_9I", line 7
ORA-06512: at line 1
Here cell1 is an object table.
Is the procedure for creating function based indexes on object tables different from relational tables?
ChinniOne of the many new features in Oracle 8i is the Function-Based Index (we will refrain from using FBI, but only just). This allows the DBA to create indexes on functions or expressions; these functions can be user generated pl/sql functions, standard SQL functions (non-aggregate only) or even a C callout.
A classic problem the DBA faces in SQL Tuning is how to tune those queries that use function calls in the where clause, and result in indexes created on these columns not to be used.
Example
Standard B-Tree index on SURNAME with cost based optimizer
create index non_fbi on sale_contacts (surname);
analyze index non_fbi compute statistics;
analyze table sale_contacts compute statistics;
SELECT count(*) FROM sale_contacts
WHERE UPPER(surname) = 'ELLISON';
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=3 Card=1 Bytes=17)
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'SALES_CONTACTS' (Cost=3 Card=16 Bytes=272)
Now we use a function based index
create index fbi on sale_contacts (UPPER(surname));
analyze index fbi compute statistics;
analyze table sale_contacts compute statistics;
SELECT count(*) FROM sale_contacts WHERE UPPER(surname) = 'ELLISON';
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1 Bytes=17)
1 0 SORT (AGGREGATE)
2 1 INDEX (RANGE SCAN) OF 'FBI' (NON-UNIQUE) (Cost=2 Card=381 Bytes=6477)
The function-based index has forced the optimizer to use index range scans (retuning zero or more rowids) on the surname column rather than doing a full table scan (non-index lookup). Optimal performance does vary depending on table size, uniqueness and selectivity of columns, use of fast full table scans etc. Therefore try both methods to gain optimal performance in your database.
It is important to remember that the function-based B*Tree index does not store the expression results in the index but uses an "expression tree". The optimizer performs expression matching by parsing the expression used in the SQL statement and comparing the results against the expression-tree values in the function-based index. This comparison IS case sensitive (ignores spaces) and therefore your function-based index expressions should match expressions used in the SQL statement where clauses.
Init.ora Parameters
The following parameter must be set in your parameter file: QUERY_REWRITE_INTEGRITY = TRUSTED
QUERY_REWRITE_ENABLED = TRUE
COMPATIBLE = 8.1.0.0.0 (or higher)
Grants
Grants To create function-based indexes the user must be granted CREATE INDEX and QUERY REWRITE, or alternatively be granted CREATE ANY INDEX and GLOBAL QUERY REWRITE. The index owner must have EXECUTE access on the function used for the index. If execute access is revoked then the function-based index will be "disabled" (see dba_indexes).
Disabled Indexes
If your function-based index has a status of "disabled" the DBA can do one of the following:
a) drop and create the index (take note of its current settings)
b) alter index enable, function-based indexes only, also use disable keyword as required
c) alter index unusable.
Queries on a DISABLED index fail if the optimizer chooses to use the index.Here is an example ORA error:
ERROR at line 1: ORA-30554: function-based index MYUSER.FBI is disabled.
All DML operations on a DISABLED index also fail unless the index is also marked UNUSABLE and the initialization parameter SKIP_UNUSABLE_INDEXES is set to true.
Some more Examples
CREATE INDEX expression_ndx
ON mytable ((mycola + mycolc) * mycolb);
SELECT mycolc FROM mytable
WHERE (mycola + mycolc) * mycolb <= 256;
..or a composite index..
CREATE INDEX example_ndx
ON myexample (mycola, UPPER(mycolb), mycolc);
SELECT mycolc FROM myexample
WHERE mycola = 55 AND UPPER(mycolb) = 'JONES';
Restriction & Rule Summary
The following restrictions apply to function based indexes. You may not index:
a) LOB columns
b) REF
c) Nested table column
d) Objects types with any of the above data types.
Function-based indexes must always follow these rules:
a) Cost Based optimizer only, must generate statistics after the index is created
b) Can not store NULL values (function can not return NULL under any circumstance)
c) If a user defined pl/sql routine is used for the function-based index, and is invalidated, the index will become "disabled"
d) Functions must be deterministic (always return the same value for a known input)
e) The index owner must have "execute" access on function used in the function-based index. Revocation of the privilege will render the index "disabled"
f) May have a B-Tree and Bitmap index type only
g) Can not use expressions that are based on aggregate functions, ie. SUM, AVG etc.
h) To alter a function-based index as enabled, the function used must be valid, deterministic and the signature of the function matches the signature of the function when it was created.
Joel P�rez -
Function based indexes doing full table scan
Guys,
I am testing function based indexes and whatever I do
it is doing a full table scan.
1)I have set the following init parameters as
QUERY_REWRITE_ENABLED=TRUE
QUERY_REWRITE_INTEGRITY=TRUSTED
2)CREATE INDEX i3 ON emp(UPPER(ename));
3) ANALYZE TABLE emp COMPUTE STATISTICS
ANALYZE INDEX I3 COMPUTE STATISTICS
4) DELETE plan_table;
5) EXPLAIN PLAN SET statement_id='Test1' FOR
SELECT ename FROM emp WHERE UPPER(ename) = 'KING';
6) SELECT LPAD(' ',2*level-2)||operation||' '||options||' '||object_name
query_plan
FROM plan_table
WHERE statement_id='Test1'
CONNECT BY prior id = parent_id
START WITH id = 0 order by id
7) And the query plan shows as
SELECT STATEMENT
TABLE ACCESS FULL EMP
I am using 9.0.1.4 !!!
Any help is appreciated !!!
Regards,
A.KishoreOne of the many new features in Oracle 8i is the Function-Based Index (we will refrain from using FBI, but only just). This allows the DBA to create indexes on functions or expressions; these functions can be user generated pl/sql functions, standard SQL functions (non-aggregate only) or even a C callout.
A classic problem the DBA faces in SQL Tuning is how to tune those queries that use function calls in the where clause, and result in indexes created on these columns not to be used.
Example
Standard B-Tree index on SURNAME with cost based optimizer
create index non_fbi on sale_contacts (surname);
analyze index non_fbi compute statistics;
analyze table sale_contacts compute statistics;
SELECT count(*) FROM sale_contacts
WHERE UPPER(surname) = 'ELLISON';
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=3 Card=1 Bytes=17)
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'SALES_CONTACTS' (Cost=3 Card=16 Bytes=272)
Now we use a function based index
create index fbi on sale_contacts (UPPER(surname));
analyze index fbi compute statistics;
analyze table sale_contacts compute statistics;
SELECT count(*) FROM sale_contacts WHERE UPPER(surname) = 'ELLISON';
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1 Bytes=17)
1 0 SORT (AGGREGATE)
2 1 INDEX (RANGE SCAN) OF 'FBI' (NON-UNIQUE) (Cost=2 Card=381 Bytes=6477)
The function-based index has forced the optimizer to use index range scans (retuning zero or more rowids) on the surname column rather than doing a full table scan (non-index lookup). Optimal performance does vary depending on table size, uniqueness and selectivity of columns, use of fast full table scans etc. Therefore try both methods to gain optimal performance in your database.
It is important to remember that the function-based B*Tree index does not store the expression results in the index but uses an "expression tree". The optimizer performs expression matching by parsing the expression used in the SQL statement and comparing the results against the expression-tree values in the function-based index. This comparison IS case sensitive (ignores spaces) and therefore your function-based index expressions should match expressions used in the SQL statement where clauses.
Init.ora Parameters
The following parameter must be set in your parameter file: QUERY_REWRITE_INTEGRITY = TRUSTED
QUERY_REWRITE_ENABLED = TRUE
COMPATIBLE = 8.1.0.0.0 (or higher)
Grants
Grants To create function-based indexes the user must be granted CREATE INDEX and QUERY REWRITE, or alternatively be granted CREATE ANY INDEX and GLOBAL QUERY REWRITE. The index owner must have EXECUTE access on the function used for the index. If execute access is revoked then the function-based index will be "disabled" (see dba_indexes).
Disabled Indexes
If your function-based index has a status of "disabled" the DBA can do one of the following:
a) drop and create the index (take note of its current settings)
b) alter index enable, function-based indexes only, also use disable keyword as required
c) alter index unusable.
Queries on a DISABLED index fail if the optimizer chooses to use the index.Here is an example ORA error:
ERROR at line 1: ORA-30554: function-based index MYUSER.FBI is disabled.
All DML operations on a DISABLED index also fail unless the index is also marked UNUSABLE and the initialization parameter SKIP_UNUSABLE_INDEXES is set to true.
Some more Examples
CREATE INDEX expression_ndx
ON mytable ((mycola + mycolc) * mycolb);
SELECT mycolc FROM mytable
WHERE (mycola + mycolc) * mycolb <= 256;
..or a composite index..
CREATE INDEX example_ndx
ON myexample (mycola, UPPER(mycolb), mycolc);
SELECT mycolc FROM myexample
WHERE mycola = 55 AND UPPER(mycolb) = 'JONES';
Restriction & Rule Summary
The following restrictions apply to function based indexes. You may not index:
a) LOB columns
b) REF
c) Nested table column
d) Objects types with any of the above data types.
Function-based indexes must always follow these rules:
a) Cost Based optimizer only, must generate statistics after the index is created
b) Can not store NULL values (function can not return NULL under any circumstance)
c) If a user defined pl/sql routine is used for the function-based index, and is invalidated, the index will become "disabled"
d) Functions must be deterministic (always return the same value for a known input)
e) The index owner must have "execute" access on function used in the function-based index. Revocation of the privilege will render the index "disabled"
f) May have a B-Tree and Bitmap index type only
g) Can not use expressions that are based on aggregate functions, ie. SUM, AVG etc.
h) To alter a function-based index as enabled, the function used must be valid, deterministic and the signature of the function matches the signature of the function when it was created.
Joel P�rez -
Is Function-based Index useless ?
I have a table with 1+ mln records, which has lastupdate (date) column.
In order to improve performance for it, I created Function-based index on Trunc(lastupdate) column:
CREATE INDEX idx_trunc_lastupdate
ON ms_test(TRUNC(LASTUPDATE))
When I run Explain Plan for my query
SELECT * FROM ms_test
WHERE trunc(lastupdate)=trunc(sysdate)
it chooses Full table scan instead of index.
Even when I include hint like this
SELECT /*+ index(MS_TEST, idx_trunc_lastupdate) */
* FROM ms_test
WHERE trunc(lastupdate)=trunc(sysdate)
Explain Plan still chooses full table scan.
What is wrong here, or maybe hints don't work with function-based indexes ?
ThanksTodd,
You're right. I can't remember when or where I read that, but I think I tested it and it was true at the time. I just tested it using 8.1.7 and, as you said, it is no longer necessary to match case and whitespace. I included my tests below.
Barbara
SQL> CREATE TABLE test_table AS SELECT created FROM user_objects
2 /
Table created.
SQL> CREATE INDEX t_fbi ON test_table (TRUNC (created))
2 /
Index created.
SQL> ANALYZE TABLE test_table
2 COMPUTE STATISTICS
3 FOR TABLE
4 FOR ALL INDEXES
5 FOR ALL INDEXED COLUMNS
6 /
Table analyzed.
SQL> ALTER SESSION SET QUERY_REWRITE_ENABLED=TRUE
2 /
Session altered.
SQL> ALTER SESSION SET QUERY_REWRITE_INTEGRITY=TRUSTED
2 /
Session altered.
SQL> SET AUTOTRACE ON EXPLAIN
SQL> SELECT COUNT (*) FROM test_table WHERE TRUNC (created) = TRUNC (SYSDATE)
2 /
COUNT(*)
3
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=1 Bytes=9)
1 0 SORT (AGGREGATE)
2 1 INDEX (RANGE SCAN) OF 'T_FBI' (NON-UNIQUE) (Cost=1 Card=
10 Bytes=90)
SQL> SELECT COUNT (*) FROM test_table WHERE trunc(created) = TRUNC (SYSDATE)
2 /
COUNT(*)
3
Execution Plan
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=1 Bytes=9)
1 0 SORT (AGGREGATE)
2 1 INDEX (RANGE SCAN) OF 'T_FBI' (NON-UNIQUE) (Cost=1 Card=
10 Bytes=90) -
How to check which function was used in a function based index.
Hi how can i check which function was used in a function based index created on a column.
ThanksHi,
What is your requirement... !!
Bascially performing a function on an indexed column in the where clause of a query guaranteed an index would not be used. From Oracle 8i onwards introduced Function Based Indexes to counter this problem.
Any how check this..you will get an idea..
http://www.akadia.com/services/ora_function_based_index_2.htm
http://www.oracle-base.com/articles/8i/FunctionBasedIndexes.php
-Pavan Kumar N -
How to create function based index on REGEXP_LIKE funtion
Dear Gurus,
I have below table CDR
Name Null Type
STARTTIME NOT NULL DATE
SUBSCRIBERNUMBER NOT NULL NUMBER
CALLINGNUMBER NOT NULL VARCHAR2(20)
CALLEDNUMBER NOT NULL VARCHAR2(20)
I am regularly firing below query
SELECT count(*)
FROM CDR data
WHERE STARTTIME BETWEEN '01-Jul-2009 00:00:00' and '31-May-2012 23:59:59'
AND REGEXP_LIKE(data.SUBSCRIBERNUMBER, '^98721[0-9]*[5]+[0-9]*$');
since there is REGEXP_LIKE is being used, Can I use function based index to improve performance.
Thanking in advance
SanjeevHi,
you can do it that way :Scott@my11g SQL>create table test (name varchar2(30));
Table created.
Scott@my11g SQL>create index myfbi on test(case when regexp_like(name,'^98721[0-9]*[5]+[0-9]*$') then 1 else 0 end);
Index created.
Scott@my11g SQL>explain plan for
2 select * from test where case when regexp_like(name,'^98721[0-9]*[5]+[0-9]*$') then 1 else 0 end = 1;
Explained.
Scott@my11g SQL>/
PLAN_TABLE_OUTPUT
Plan hash value: 140237472
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 20 | 1 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 20 | 1 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | MYFBI | 1 | | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access(CASE WHEN REGEXP_LIKE ("NAME",'^98721[0-9]*[5]+[0-9]*$')
THEN 1 ELSE 0 END =1)
Note
- dynamic sampling used for this statement (level=2)
19 rows selected.
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