SQL Plan Management (11.2.0.1)

Question

Hi Guys,
I'm doing some testing as below.
I tried to keep the SQL plan in baseline. (when the table has no index, as such performing full scan)
However, after i create the index. It's not picking the original plan which i put it in baseline. It's using range scan.
Can advise what have i done wrong?
thanks!
SQL> show parameter OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES;
NAME TYPE VALUE
optimizer_capture_sql_plan_baselines boolean FALSE
SQL> CREATE TABLE spm_test_tab (
2 id NUMBER,
3 description VARCHAR2(50)
4 );
Table created.
SQL>
SQL> DECLARE
2 TYPE t_tab IS TABLE OF spm_test_tab%ROWTYPE;
3 l_tab t_tab := t_TAB();
4 BEGIN
5 FOR i IN 1 .. 10000 LOOP
6 l_tab.extend;
7 l_tab(l_tab.last).id := i;
8 l_tab(l_tab.last).description := 'Description for ' || i;
9 END LOOP;
10
11 FORALL i IN l_tab.first .. l_tab.last
12 INSERT INTO spm_test_tab VALUES l_tab(i);
13
14 COMMIT;
15 END;
16 /
PL/SQL procedure successfully completed.
SQL>
SQL> EXEC DBMS_STATS.gather_table_stats(USER, 'SPM_TEST_TAB', cascade=>TRUE);
PL/SQL procedure successfully completed.
SQL> set linesize 2000
SQL> set pagesize 2000
SQL> SET AUTOTRACE TRACE
SQL>
SQL> SELECT description
2 FROM spm_test_tab
3 WHERE id = 99;
Execution Plan
Plan hash value: 3128910679
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 25 | 13 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| SPM_TEST_TAB | 1 | 25 | 13 (0)| 00:00:01 |
Predicate Information (identified by operation id):
1 - filter("ID"=99)
Statistics
26 recursive calls
5 db block gets
49 consistent gets
0 physical reads
944 redo size
228 bytes sent via SQL*Net to client
239 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL>
SQL> set autotrace off;
SQL>
SQL> SELECT sql_id, sql_text
2 FROM v$sql
3 WHERE sql_text LIKE '%spm_test_tab%'
4 AND sql_text NOT LIKE '%dba_sql_plan_baselines%'
5 AND sql_text NOT LIKE '%EXPLAIN%';
SQL_ID SQL_TEXT
gat6z1bc6nc2d SELECT description FROM spm_test_tab WHERE id = 99
44b32kmh8ub2g DECLARE TYPE t_tab IS TABLE OF spm_test_tab%ROWTYPE; l_tab t_tab := t_TAB(); BEGIN
SQL> SET SERVEROUTPUT ON
SQL> DECLARE
2 l_plans_loaded PLS_INTEGER;
3 BEGIN
4 l_plans_loaded := DBMS_SPM.load_plans_from_cursor_cache(
5 sql_id => 'gat6z1bc6nc2d');
6
7 DBMS_OUTPUT.put_line('Plans Loaded: ' || l_plans_loaded);
8 END;
9 /
Plans Loaded: 1
PL/SQL procedure successfully completed.
SQL> SELECT sql_handle, plan_name, enabled, accepted
2 FROM dba_sql_plan_baselines
3 WHERE sql_text LIKE '%spm_test_tab%'
4 AND sql_text NOT LIKE '%dba_sql_plan_baselines%';
SQL_HANDLE PLAN_NAME ENA ACC
SYS_SQL_7b76323ad90440b9 SQL_PLAN_7qxjk7bch8h5tb65c37c8 YES YES
SQL>
SQL> ALTER SYSTEM FLUSH SHARED_POOL;
System altered.
SQL>
SQL> CREATE INDEX spm_test_tab_idx ON spm_test_tab(id);
Index created.
SQL> EXEC DBMS_STATS.gather_table_stats(USER, 'SPM_TEST_TAB', cascade=>TRUE);
PL/SQL procedure successfully completed.
SQL>
SQL> SET AUTOTRACE TRACE
SQL>
SQL> SELECT description
2 FROM spm_test_tab
3 WHERE id = 99;
Execution Plan
Plan hash value: 2792204123
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 25 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| SPM_TEST_TAB | 1 | 25 | 2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | SPM_TEST_TAB_IDX | 1 | | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access("ID"=99)
Statistics
1072 recursive calls
3 db block gets
192 consistent gets
0 physical reads
888 redo size
242 bytes sent via SQL*Net to client
239 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
18 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> set autotrace off;
SQL> SELECT sql_handle, plan_name, enabled, accepted
2 FROM dba_sql_plan_baselines
3 ;
SQL_HANDLE PLAN_NAME ENA ACC
SYS_SQL_7b76323ad90440b9 SQL_PLAN_7qxjk7bch8h5tb65c37c8 YES YES

Answer 1

Check the value of OPTIMIZER_USE_SQL_PLAN_BASELINES.
Double check the sql id and exact matching signature of both statements .
Turn autotrace off, execute statement then use:
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST'));to get the actual execution plan of the last executed statement in that session
If in doubt, enable a SQL Plan Management trace:
alter session set events 'trace[RDBMS.SQL_Plan_Management.*]';