Hints, Patches, Force Matching and SQL Profiles

Sometimes, when all else fails, it is necessary to add hints to a piece of SQL in order to make the optimizer use a particular execution plan. We might directly add the hint to the code. However, even if it is possible to access the code directly, that may not be a good idea. In the future, if we need to change the hint, possibly due to a change in optimizer behaviour on database upgrade, then we would again need to make a code change.
Instead, we could look at Oracle's plan stability technologies.  There are 4 plan stability features in the database. They are different, but conceptually they all involve associating a set of hints with a statement that will be picked up by the optimizer at runtime.

• SQL Outlines can be collected by the database at runtime. They can exactly match a SQL text or force match. However, they are deprecated from 11g. 
• SQL Baselines can be collected by the database at runtime either on request or automatically. They feed real experience of previous executions of a statement back into subsequent executions. They match by SQL_ID. 
• SQL Patches are a mechanism for manually inserting specific hints into a specific SQL ID 
• SQL Profiles are also a mechanism for inserting specific hints into a specific SQL statement, but can also do forced matching. We are probably most used to creating profiles with Carlos Sierra's coe_xfr_sql_profile.sql script (part of Oracle support's SQLTXPLAIN), but as this blog will show that is not the only option. However, they require the database tuning pack to be licenced, which is not the case with the other mechanisms. 

There are several posts on Oracle's optimizer team that blog explains how to use SQL patches to inject a hint or disable an embedded hint.

• SQL Plan Management (Part 4 of 4) User Interfaces and Other Features (Feb 2009): Maria Colgan described the DBMS_SPM package, and how baselines are captured, evolved and can be accepted. 
• Using SQL Patch to add hints to a packaged application (June 2017): Nigel Bayliss describes the new DBMS_SQLDIAG API in Oracle 12.2 to add SQL patches to specific SQL statements, but everything works the same in the internal package as described in Maria's earlier blogs: 
• Using SQL Patch to add hints to a packaged application (Feb 2012) describes adding patches with the DBMS_SQLDIAG_INTERNAL package. 
• Additional Information on SQL Patches (Mar 2012)  

However, the SQL patches work by attaching to a specific SQL_ID. If your application has literal values that change instead of bind variables you will not be able to inject hints with SQL patches.
The following example SQL was generated by PeopleSoft GL reporting tool, nVision. The code is dynamically generated by the tool, and there is no way to add a hint directly. The generated code contains literal values, in particular, the SELECTOR_NUM will be different for every execution. Therefore the SQL_ID will be different for every execution. Therefore, it is not possible to use a SQL Patch to inject a hint.

SELECT L2.TREE_NODE_NUM,L3.TREE_NODE_NUM,SUM(A.POSTED_TOTAL_AMT) 
FROM PS_XX_SUM_CONSOL_VW A, PSTREESELECT05 L2, PSTREESELECT10 L3 
WHERE A.LEDGER='S_USMGT' 
AND A.FISCAL_YEAR=2017 
AND A.ACCOUNTING_PERIOD BETWEEN 0 AND 12 
AND (A.DEPTID BETWEEN 'A0000' AND 'A8999' OR A.DEPTID BETWEEN 'B0000' AND 'B9149' 
OR A.DEPTID='B9156' OR A.DEPTID='B9158' OR A.DEPTID BETWEEN 'B9165' AND 'B9999' 
OR A.DEPTID BETWEEN 'C0000' AND 'C9999' OR A.DEPTID BETWEEN 'D0000' AND 'D9999' 
OR A.DEPTID BETWEEN 'G0000' AND 'G9999' OR A.DEPTID BETWEEN 'H0000' AND 'H9999' 
OR A.DEPTID='B9150' OR A.DEPTID=' ') 
AND L2.SELECTOR_NUM=10228 
AND A.BUSINESS_UNIT=L2.RANGE_FROM_05 
AND L3.SELECTOR_NUM=10231 
AND A.ACCOUNT=L3.RANGE_FROM_10 
AND A.CHARTFIELD1='0012345' 
AND A.CURRENCY_CD='GBP' 
GROUP BY L2.TREE_NODE_NUM,L3.TREE_NODE_NUM
/

If only the literal values differ, then the SQL statements will have the same force matching signature and one SQL profile will match all similar statements. Although, statements will not force match if the number of predicates changes. Nonetheless, I can inject hints with a SQL profile. This is the plan I get initially without a profile. It doesn't perform well, and it is not the plan I want.

Plan hash value: 808840077
-----------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                                     | Name              | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
-----------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                              |                   |       |       | 10408 (100)|          |       |       |
|   1 |  HASH GROUP BY                                |                   |   517 | 50666 | 10408   (1)| 00:00:01 |       |       |
|   2 |   HASH JOIN                                   |                   |   517 | 50666 | 10407   (1)| 00:00:01 |       |       |
|   3 |    PARTITION RANGE SINGLE                     |                   |   731 | 13158 |     3   (0)| 00:00:01 | 10228 | 10228 |
|   4 |     INDEX FAST FULL SCAN                      | PSAPSTREESELECT05 |   731 | 13158 |     3   (0)| 00:00:01 | 10228 | 10228 |
|   5 |    HASH JOIN                                  |                   |   518 | 41440 | 10404   (1)| 00:00:01 |       |       |
|   6 |     PARTITION RANGE SINGLE                    |                   |   249 |  5727 |     2   (0)| 00:00:01 | 10231 | 10231 |
|   7 |      INDEX FAST FULL SCAN                     | PSAPSTREESELECT10 |   249 |  5727 |     2   (0)| 00:00:01 | 10231 | 10231 |
|   8 |     PARTITION RANGE ITERATOR                  |                   |  7785 |   433K| 10402   (1)| 00:00:01 |    28 |    40 |
|   9 |      TABLE ACCESS BY LOCAL INDEX ROWID BATCHED| PS_X_LEDGER_ACCTS |  7785 |   433K| 10402   (1)| 00:00:01 |    28 |    40 |
|  10 |       SORT CLUSTER BY ROWID BATCHED           |                   |  5373 |       |  5177   (1)| 00:00:01 |       |       |
|  11 |        INDEX SKIP SCAN                        | PS_X_LEDGER_ACCTS |  5373 |       |  5177   (1)| 00:00:01 |    28 |    40 |
-----------------------------------------------------------------------------------------------------------------------------------

These are the hints I want to introduce. I want to force materialize view rewrite, invoke parallelism if the statement is estimated to run for at least 2 seconds, and use a Bloom filter on the materialized view.

SELECT /*+OPT_PARAM('parallel_degree_policy','AUTO') OPT_PARAM('parallel_min_time_threshold',2) 
OPT_PARAM('parallel_degree_limit',4) REWRITE PX_JOIN_FILTER(PS_XX_SUM_GCNSL_MV)*/…

This application produces many statements that I may want to control with a profile, but with forced matching this comes down to a not unmanageable number.  I have created a data-driven framework to create the profiles. I have created working storage table into which I will populate it with details of each force matching signature for which I want to create a profile.

CREATE TABLE dmk_fms_profiles
(force_matching_signature    NUMBER NOT NULL
,sql_id                      VARCHAR2(13) 
,plan_hash_value             NUMBER
,module                      VARCHAR2(64)
,report_id                   VARCHAR2(32) /*Application Specific*/
,tree_list                   CLOB         /*Application Specific*/
,sql_profile_name            VARCHAR2(30)
,parallel_min_time_threshold NUMBER
,parallel_degree_limit       NUMBER
,other_hints                 CLOB
,delete_profile              VARCHAR2(1)
,sql_text                    CLOB
,CONSTRAINT dmk_fms_profiles_pk PRIMARY KEY (force_matching_signature)
,CONSTRAINT dmk_fms_profiles_u1 UNIQUE (sql_id)
,CONSTRAINT dmk_fms_profiles_u2 UNIQUE (sql_profile_name)
)
/

Using conditional parallelism with the PARALLEL_MIN_TIME_THRESHOLD, but limited with PARALLEL_DEGREE_LIMIT is a frequently used tactic with this application, so I have specified columns for those hints, otherwise, hints are injected via a string. I identified the problematic SQL by analysis with ASH, and hence I also obtained the FORCE_MATCHING_SIGNATURE for them. The metadata is keyed by FORCE_MATCHING_SIGNATURE. I am specifying an additional hint to force materialized view rewrite and use a Bloom filter on the ledger table. I have specified a meaningful name for the SQL profile.

INSERT INTO dmk_fms_profiles (force_matching_signature, parallel_min_time_threshold, parallel_degree_limit, other_hints, sql_profile_name) 
VALUES (16625752171077499412, 1, 4, 'REWRITE PX_JOIN_FILTER(PS_FT_SUM_GCNSL_MV)', 'NVS_GBGL123I_BU_CONSOL_ACCOUNT');
COMMIT;

Profiles are created on the text of a SQL rather than the SQL_ID or FORCE_MATCHING_SIGNATURE directly. Therefore the SQL_TEXT must be extracted from the AWR, so this method also requires that the statement has been captured by an AWR snapshot.

UPDATE dmk_fms_profiles a
SET    (module, action, sql_id, plan_hash_value, sql_text)
=      (SELECT s.module, s.action, s.sql_id, s.plan_hash_value, t.sql_text
        FROM   dba_hist_sqlstat s
        ,      dba_hist_sqltext t
        WHERE  t.dbid = s.dbid
        AND    t.sql_id = s.sql_id
        AND    s.force_matching_signature = a.force_matching_signature
        AND    s.snap_id = (
   SELECT MAX(s1.snap_id)
  FROM   dba_hist_sqlstat s1
  WHERE  s1.force_matching_signature = a.force_matching_signature
  AND    s1.module = 'RPTBOOK'     /*Application Specific*/
   AND    s1.action LIKE 'PI=%:%:%' /*Application Specific*/)
  AND    s.module = 'RPTBOOK'             /*Application Specific*/
  AND    s.action LIKE 'PI=%:%:%'         /*Application Specific*/
  AND    ROWNUM = 1)
WHERE sql_id IS NULL
/

MERGE INTO dmk_fms_profiles u
USING (
SELECT a.sql_id, a.force_matching_signature, p.name
FROM   dmk_fms_profiles a
,      dba_sql_profiles p
WHERE  p.signature = a.force_matching_signature
) s
ON (s.force_matching_signature = u.force_matching_signature)
WHEN MATCHED THEN UPDATE
SET u.sql_profile_name = s.name
/

Columns REPORT_ID and TREE_LIST contain application specific information extracted from the application instrumentation and logging. They only mean something in the context of the application.

/*Application Specific - extract report ID from ACTION*/
UPDATE dmk_fms_profiles a
SET    report_id = substr(regexp_substr(s.action,':([A-Za-z0-9_-])+',1,1),2)
WHERE  report_id IS NULL
AND    action IS NOT NULL
/

Now I can produce a simple report of the metadata in order to see what profiles should be created.

column sql_text word_wrapped on format a110
column module format a8
column report_id heading 'nVision|Report ID'
column tree_list word_wrapped on format a20
column plan_hash_value             heading 'SQL Plan|Hash Value'         format 9999999999
column parallel_min_time_threshold heading 'Parallel|Min Time|Threshold' format 999
column parallel_degree_limit       heading 'Parallel|Degree|Limit'       format 999
set long 500
SELECT * FROM dmk_fms_profiles
/

                                          SQL Plan                                                                           
FORCE_MATCHING_SIGNATURE SQL_ID         Hash Value MODULE   ACTION                                                           
------------------------ ------------- ----------- -------- ---------------------------------------------------------------- 
                                                                                      Parallel Parallel
nVision                                                                               Min Time   Degree
Report ID                        TREE_LIST            SQL_PROFILE_NAME               Threshold    Limit D
-------------------------------- -------------------- ------------------------------ --------- -------- -
OTHER_HINTS
--------------------------------------------------------------------------------
SQL_TEXT
--------------------------------------------------------------------------------------------------------------
    12803175998948432502 5pzxhha3392cs   988048519 RPTBOOK  PI=3186222:USGL233I:10008                                        
USGL233I                         BU_GAAP_CONSOL,      NVS_GBGL123I_BU_CONSOL_ACCOUNT                   1        4
                                 GAAP_ACCOUNT
REWRITE PX_JOIN_FILTER(PS_XX_SUM_GCNSL_MV)
SELECT L2.TREE_NODE_NUM,A.ACCOUNT,SUM(A.POSTED_TOTAL_AMT) FROM PS_LEDGER A, PSTREESELECT05 L2, PSTREESELECT10 L3
WHERE A.LEDGER='S_GBMGT' AND A.FISCAL_YEAR=2017 AND A.ACCOUNTING_PERIOD BETWEEN 0 AND 12 AND (A.DEPTID BETWEEN
'A0000' AND 'A8999' OR A.DEPTID BETWEEN 'B0000' AND 'B9149' OR A.DEPTID='B9156' OR A.DEPTID='B9158' OR A.DEPTID
BETWEEN 'B9165' AND 'B9999' OR A.DEPTID BETWEEN 'C0000' AND 'C9999' OR A.DEPTID BETWEEN 'D0000' AND 'D9999' OR
A.DEPTID BETWEEN 'G0000' AND 'G9999' OR A.DE

Next, this PL/SQL block will create or recreate SQL profiles from the metadata. The various hints can be concatenated into a single string and passed as a parameter to SQLPROF_ATTR. The SQL text is passed as a parameter when the profile is created.

set serveroutput on
DECLARE
  l_signature NUMBER;
  h       SYS.SQLPROF_ATTR;
  e_no_sql_profile EXCEPTION;
  PRAGMA EXCEPTION_INIT(e_no_sql_profile, -13833);
  l_description CLOB;
BEGIN

FOR i IN (
  SELECT f.*, s.name
  FROM   dmk_fms_profiles f
    LEFT OUTER JOIN dba_sql_profiles s
    ON f.force_matching_signature = s.signature
) LOOP

  BEGIN 
    IF i.name IS NOT NULL AND i.delete_profile = 'Y' THEN
      dbms_sqltune.drop_sql_profile(name => i.name);
    END IF;
    EXCEPTION WHEN e_no_sql_profile THEN NULL;
  END;

  IF i.delete_profile = 'Y' THEN 
    NULL;
  ELSIF i.sql_text IS NOT NULL THEN
    h := SYS.SQLPROF_ATTR(
q'[BEGIN_OUTLINE_DATA]',
CASE WHEN i.parallel_min_time_threshold>=0 THEN 'OPT_PARAM(''parallel_degree_policy'',''AUTO'') ' END||
CASE WHEN i.parallel_degree_limit      >=0 THEN 'OPT_PARAM(''parallel_degree_limit'','      ||i.parallel_degree_limit      ||') ' END||
CASE WHEN i.parallel_min_time_threshold>=0 THEN 'OPT_PARAM(''parallel_min_time_threshold'','||i.parallel_min_time_threshold||') ' END||
i.other_hints,
q'[END_OUTLINE_DATA]');

    l_signature := DBMS_SQLTUNE.SQLTEXT_TO_SIGNATURE(i.sql_text);
    l_description := 'coe nVision '||i.report_id||' '||i.tree_list||' '||i.force_matching_signature||'='||l_signature;
    dbms_output.put_line(i.sql_profile_name||' '||l_description);

    DBMS_SQLTUNE.IMPORT_SQL_PROFILE (
sql_text    => i.sql_text,
profile     => h,
name        => i.sql_profile_name,
description => l_description,
category    => 'DEFAULT',
validate    => TRUE,
replace     => TRUE,
force_match => TRUE /* TRUE:FORCE (match even when different literals in SQL). FALSE:EXACT (similar to CURSOR_SHARING) */ );

  END IF;
END LOOP;
END;
/

I can verify that the profile has been created, and the hints that it contains, thus:

SELECT profile_name,
       xmltype(comp_data) as xmlval
FROM   dmk_fms_profiles p
,      dbmshsxp_sql_profile_attr  x
WHERE  x.profile_name = p.sql_profile_name
AND    p.status = 'ENABLED'
ORDER BY 1
/

PROFILE_NAME                                                                                                                                                                                            
------------------------------
XMLVAL                                                                                                                                                                                                  
------------------------------------------------------------------------------------------------
NVS_GBGL123I_BU_CONSOL_ACCOUNT
<![CDATA[BEGIN_OUTLINE_DATA]]>                                                                                                                                                           
  <![CDATA[OPT_PARAM('parallel_degree_policy','AUTO') OPT_PARAM('parallel_degree_limit',4) OPT_PARAM('parallel_min_time_threshold',1) REWRITE PX_JOIN_FILTER(PS_FT_SUM_GCNSL_MV)]]>                                           
  <![CDATA[END_OUTLINE_DATA]]>

And now when the application runs, I get the plan that I wanted.

• The query runs in parallel.
• The SQL is rewritten to use materialized view.
• There are no indexes so it must full scan it.
• It generates a bloom filter from PSTREESELECT10 and applies it to the materialized view.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                                         | Name               | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |    TQ  |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                                  |                    |       |       |  2219 (100)|          |       |       |        |      |            |
|   1 |  PX COORDINATOR                                   |                    |       |       |         |             |       |       |        |      |            |
|   2 |   PX SEND QC (RANDOM)                             | :TQ10004           |   111 |  9879 |  2219   (6)| 00:00:01 |       |       |  Q1,04 | P->S | QC (RAND)  |
|   3 |    HASH GROUP BY                                  |                    |   111 |  9879 |  2219   (6)| 00:00:01 |       |       |  Q1,04 | PCWP |            |
|   4 |     PX RECEIVE                                    |                    |   111 |  9879 |  2219   (6)| 00:00:01 |       |       |  Q1,04 | PCWP |            |
|   5 |      PX SEND HASH                                 | :TQ10003           |   111 |  9879 |  2219   (6)| 00:00:01 |       |       |  Q1,03 | P->P | HASH       |
|   6 |       HASH GROUP BY                               |                    |   111 |  9879 |  2219   (6)| 00:00:01 |       |       |  Q1,03 | PCWP |            |
|   7 |        HASH JOIN                                  |                    |   536 | 47704 |  2218   (6)| 00:00:01 |       |       |  Q1,03 | PCWP |            |
|   8 |         PX RECEIVE                                |                    |   536 | 38056 |  2215   (6)| 00:00:01 |       |       |  Q1,03 | PCWP |            |
|   9 |          PX SEND HYBRID HASH                      | :TQ10002           |   536 | 38056 |  2215   (6)| 00:00:01 |       |       |  Q1,02 | P->P | HYBRID HASH|
|  10 |           STATISTICS COLLECTOR                    |                    |       |       |         |             |       |       |  Q1,02 | PCWC |            |
|  11 |            HASH JOIN                              |                    |   536 | 38056 |  2215   (6)| 00:00:01 |       |       |  Q1,02 | PCWP |            |
|  12 |             BUFFER SORT                           |                    |       |       |         |             |       |       |  Q1,02 | PCWC |            |
|  13 |              JOIN FILTER CREATE                   | :BF0000            |   236 |  3776 |     2   (0)| 00:00:01 |       |       |  Q1,02 | PCWP |            |
|  14 |               PX RECEIVE                          |                    |   236 |  3776 |     2   (0)| 00:00:01 |       |       |  Q1,02 | PCWP |            |
|  15 |                PX SEND BROADCAST                  | :TQ10000           |   236 |  3776 |     2   (0)| 00:00:01 |       |       |        | S->P | BROADCAST  |
|  16 |                 PARTITION RANGE SINGLE            |                    |   236 |  3776 |     2   (0)| 00:00:01 | 36774 | 36774 |        |      |            |
|  17 |                  INDEX FAST FULL SCAN             | PSAPSTREESELECT10  |   236 |  3776 |     2   (0)| 00:00:01 | 36774 | 36774 |        |      |            |
|  18 |             JOIN FILTER USE                       | :BF0000            |  8859 |   475K|  2213   (6)| 00:00:01 |       |       |  Q1,02 | PCWP |            |
|  19 |              PX BLOCK ITERATOR                    |                    |  8859 |   475K|  2213   (6)| 00:00:01 |    29 |    41 |  Q1,02 | PCWC |            |
|  20 |               MAT_VIEW REWRITE ACCESS STORAGE FULL| PS_XX_SUM_GCNSL_MV |  8859 |   475K|  2213   (6)| 00:00:01 |    29 |    41 |  Q1,02 | PCWP |      
|  21 |         BUFFER SORT                               |                    |       |       |         |             |       |       |  Q1,03 | PCWC |            |
|  22 |          PX RECEIVE                               |                    |   731 | 13158 |     3   (0)| 00:00:01 |       |       |  Q1,03 | PCWP |            |
|  23 |           PX SEND HYBRID HASH                     | :TQ10001           |   731 | 13158 |     3   (0)| 00:00:01 |       |       |        | S->P | HYBRID HASH|
|  24 |            PARTITION RANGE SINGLE                 |                    |   731 | 13158 |     3   (0)| 00:00:01 | 36773 | 36773 |        |      |            |
|  25 |             INDEX FAST FULL SCAN                  | PSAPSTREESELECT05  |   731 | 13158 |     3   (0)| 00:00:01 | 36773 | 36773 |        |      |            |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

Conclusion SQL 

Profiles can be used in much the same way as SQL Patches to introduce hints into application SQL without changing the code, the difference being that SQL Profiles can force match SQL. However, SQL Profiles do require the Tuning pack to be licenced, whereas SQL Patches do not. Some hints do not work because the profile is applied to late in the parse process. For example, if you use cursor sharing then the CURSOR_SHARING_EXACT hint will not take effect.

Changing Physical Index Attributes without Down Time

Normally, we make an index invisible before we drop it, in order to see whether we can manage without it, and if not we can make it visible again.  In this blog, I will demonstrate how to use index invisibility to introduce an index change that I cannot do with an online operation.  I am also able to reverse it immediately, whereas an on-line operation would take time.

Problem Statement

I have a large partitioned table, but the primary key index on it was not partitioned.  Testing has shown that performance would improve if the index was locally partitioned.  It is not possible to introduce the partitioning by rebuilding the index online.  I cannot afford the downtime to drop and rebuild the index, and anyway I want an easy way back to the original state in case of a problem.

Demonstration

I encountered this problem in a PeopleSoft system with a unique index, but here I will demonstrate it with a primary key constraint also.  I will create and populate a simple range partitioned table with a primary key constraint.

DROP TABLEt PURGE;

CREATE TABLE t
(a number not null
,b number not null
,c number
,d number) 
partition by range (a) interval (42)
(partition values less than (42))
/
ALTER TABLE t ADD CONSTRAINT t_pk PRIMARY KEY (a,b)
/
TRUNCATE TABLE t
/
INSERT INTO t
WITH x AS (select rownum n from dual connect by level <= 100)
SELECT a.n, b.n, a.n*b.n, a.n+b.n
FROM x a, x b
/

Note that table is partitioned, but the unique index is not. I haven't had to explicitly build it without partitioning.

set long 5000
select dbms_metadata.get_ddl('INDEX','T_PK')
from dual
/
CREATE UNIQUE INDEX "SCOTT"."T_PK" ON "SCOTT"."T" ("A", "B")
PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
TABLESPACE "USERS"

I cannot just create the new index because the column list is already indexed.

CREATE UNIQUE INDEX SCOTT.T_PK_NEW ON SCOTT.T (A, B)
                                               *
ERROR at line 1:
ORA-01408: such column list already indexed

So, now I will create a new unique index on the same columns, but I will create it invisible. I will also create it online so that I do not block the application from performing DML on the table while the index is built.

CREATE UNIQUE INDEX SCOTT.T_PK_NEW ON SCOTT.T (A, B)
LOCAL INVISIBLE ONLINE
/

So now I have two unique indexes, one visible, one invisible

set autotrace off
column constraint_name format a20
column table_name format a10
column index_name format a10
SELECT index_name, visibility FROM user_indexes WHERE table_name = 'T'
/

INDEX_NAME VISIBILIT
---------- ---------
T_PK       VISIBLE
T_PK_NEW   INVISIBLE

I cannot make the new index visible while the original index is also visible because I cannot have two unique indexes

ALTER INDEX SCOTT.T_PK_NEW VISIBLE
/
*
ERROR at line 1:
ORA-14147: There is an existing VISIBLE index defined on the same set of columns.

Instead, I have to make the original index invisible first. However, even if both indexes are invisible the unique constraint is still enforced.

ALTER INDEX SCOTT.T_PK INVISIBLE
/
INSERT INTO t VALUES (1,2,3,4)
/
*
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.T_PK) violated

ALTER INDEX SCOTT.T_PK_NEW VISIBLE
/

Now my new index is visible.

SELECT index_name, visibility FROM user_indexes WHERE table_name = 'T'
/

INDEX_NAME VISIBILIT
---------- ---------
T_PK       INVISIBLE
T_PK_NEW   VISIBLE

The constraint still points to the original index.

INSERT INTO t VALUES(1,2,3,4)
/
*
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.T_PK) violated

SELECT constraint_name, table_name, index_name
FROM   user_constraints
WHERE  constraint_name = 'T_PK'
/

CONSTRAINT_NAME      TABLE_NAME INDEX_NAME
-------------------- ---------- ----------
T_PK                 T          T_PK

However, queries now use the new index.

set autotrace on lines 160
SELECT * FROM t WHERE a = 1 and b=2
/
Plan hash value: 3024084754
---------------------------------------------------------------------------------------------------------------
| Id  | Operation                          | Name     | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
---------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                   |          |     1 |    52 |     2   (0)| 00:00:01 |       |       |
|   1 |  PARTITION RANGE SINGLE            |          |     1 |    52 |     2   (0)| 00:00:01 |     1 |     1 |
|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| T        |     1 |    52 |     2   (0)| 00:00:01 |     1 |     1 |
|*  3 |    INDEX UNIQUE SCAN               | T_PK_NEW |     1 |       |     1   (0)| 00:00:01 |     1 |     1 |
---------------------------------------------------------------------------------------------------------------

The original index can now be removed. However, unique indexes used by primary key constraints cannot be dropped directly. Instead the modifying the primary key constraint drops the original index.

ALTER TABLE scott.t 
MODIFY CONSTRAINT t_pk USING INDEX t_pk_new
/

SELECT constraint_name, table_name, index_name
FROM   user_constraints
WHERE  constraint_name = 'T_PK'
/
CONSTRAINT_NAME      TABLE_NAME INDEX_NAME
-------------------- ---------- ----------
T_PK                 T          T_PK_NEW

SELECT index_name, visibility FROM user_indexes WHERE table_name = 'T'
/

INDEX_NAME VISIBILIT
---------- ---------
T_PK_NEW   VISIBLE

Finally, the new index can be renamed.

ALTER INDEX t_pk_new RENAME TO t_pk
/