Using hints with coe_xfr_sql_profile.sql

In an earlier blog post I showed how I used coe_xfr_sql_profile.sql from the sqlt toolkit from Oracle support to force a particular sql statement to run with a more efficient plan that it had used in the past.

Today, I’m trying a slight variation.  Take the problem query, run it with hints, and use coe_xfr_sql_profile.sql to apply the resulting plan to the original query.  I built a quick and dirty test to make sure it works.

-- create test table with index and stats

SQL> create table test as select * from dba_tables;

SQL> create index testi on test(owner);

SQL> execute dbms_stats.gather_table_stats(NULL,'TEST');

-- run query unhinted

SQL> select sum(blocks) from test where owner='SYS';

SUM(BLOCKS)
-----------
    1042402

-- show plan - uses the index

SQL> select * from 
table(dbms_xplan.display_cursor(null,null,'ALL'));

PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  a0nw2xjnmjcxd, child number 0
-------------------------------------
select sum(blocks) from test where owner='SYS'

Plan hash value: 1551939256

--------------------------------------------------------------
| Id  | Operation                    | Name  | Rows  | Bytes |
--------------------------------------------------------------
|   0 | SELECT STATEMENT             |       |       |       |
|   1 |  SORT AGGREGATE              |       |     1 |     9 |
|   2 |   TABLE ACCESS BY INDEX ROWID| TEST  |  2122 | 19098 |
|*  3 |    INDEX RANGE SCAN          | TESTI |  2122 |       |
--------------------------------------------------------------

-- use hint to force full scan

SQL> select /*+full(test) */ sum(blocks) from test 
where owner='SYS';

SUM(BLOCKS)
-----------
    1042402

-- get plan with full scan

SQL> select * from 
table(dbms_xplan.display_cursor(null,null,'ALL'));

PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  5521zhmq67vun, child number 0
-------------------------------------
select /*+full(test) */ sum(blocks) from test 
where owner='SYS'

Plan hash value: 3467505462

----------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)|
----------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |   295 (100)|
|   1 |  SORT AGGREGATE    |      |     1 |     9 |            |
|*  2 |   TABLE ACCESS FULL| TEST |  2122 | 19098 |   295   (1)|
----------------------------------------------------------------

So, let’s pretend that sql_id=a0nw2xjnmjcxd is the real production query you are trying to tune.  Without hints it is doing an index range scan.  With a hint you run a similar query forcing a full scan.  The new query, sql_id=5521zhmq67vun has a plan with this hash value: 3467505462.  So, I used coe_xfr_sql_profile.sql to force the unhinted original query to run with the hinted query’s plan:

cd /var/opt/oracle/admin/sqlt/utl

-- login to sqlplus as system

@coe_xfr_sql_profile.sql a0nw2xjnmjcxd 3467505462

-- login to sqlplus as system

@coe_xfr_sql_profile_a0nw2xjnmjcxd_3467505462.sql

Now when I run the original query it runs with the new plan and indicates that the profile is in use:

SQL> select sum(blocks) from test where owner='SYS';

SUM(BLOCKS)
-----------
    1042402

SQL> select * from 
table(dbms_xplan.display_cursor(null,null,'ALL'));

PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  a0nw2xjnmjcxd, child number 0
-------------------------------------
select sum(blocks) from test where owner='SYS'

Plan hash value: 3467505462

----------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)|
----------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |   295 (100)|
|   1 |  SORT AGGREGATE    |      |     1 |     9 |            |
|*  2 |   TABLE ACCESS FULL| TEST |  2122 | 19098 |   295   (1)|
----------------------------------------------------------------

Note
-----
   - SQL profile coe_a0nw2xjnmjcxd_3467505462 used for 
     this statement

I edited the output to make it more readable.  See the zip with the full scripts and logs.

So, if you have a recurring production SQL query that runs faster with hints just run that query once with the hints and then use coe_xfr_sql_profile.sql to force the real query to run unchanged but with the same plan as the hinted query.

– Bobby

 

 

 

 

 

 

 

 

 

 

 

 

 

About Bobby

I live in Chandler, Arizona with my wife and three daughters. I work for US Foods, the second largest food distribution company in the United States. I've been working as an Oracle database administrator and PeopleSoft administrator since 1994. I'm very interested in Oracle performance tuning.
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