Dbms_xplan.display_awr display more than one plan

Question

Hi,
There are times when running dbms_xplan.display_awr , shows more than one execution plan.
How can i know which of the plans is the most recent ?
For example :
SYS@qa> SELECT * FROM table(dbms_xplan.display_awr('0gtqfjcypx66z'));
Show two diffrenets plan :
Plan hash value: 3366355658
Plan hash value: 2273523394
Thanks

Answer 1

It is more than likely both plan will be relevant. A single sql_id does not mean that there is a single plan active.
Below is a very simple testcase that highlights the same sql_id with 2 different plans being used at the same time. Even though the same namespace is shared the underlying objects are different.
There are a lot of other reasons for a child cursor to not be shared apart from the query be executed in different schema.
-- 1. Create 2 users with identical tables but different data. 1 table has an index.
sqlplus / as sysdba
grant dba to test1 identified by test;
grant dba to test2 identified by test;
create table test1.x (x varchar2(1));
create table test2.x (x varchar2(1));
declare
i number;
begin
for i in 1..125000 loop
insert into test1.x values ('N');
end loop;
insert into test1.x values ('Y');
commit;
end;
insert into test2.x values('T');
create index test1.x_idx on test1.x(x);
exec dbms_stats.gather_table_stats('TEST1','X', method_opt=>'for all columns size skewonly');
exec dbms_stats.gather_table_stats('TEST2','X');
alter system flush shared_pool;
-- Connect as the first user and observe the results
conn test1/test
select * from x where x='Y';
SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR);
alter session set nls_date_format='DD-MON-YYYY:HH24:MI:SS';
select sql_id, PLAN_HASH_VALUE,CHILD_NUMBER,LOADS,USERS_EXECUTING,FIRST_LOAD_TIME,LAST_ACTIVE_TIME, OPEN_VERSIONS from v$sql where sql_text like 'select * from x%';
pause
-- Connect as the second user. See the second child cursor being created with a different plan
conn test2/test
select * from x where x='Y';
SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR);
alter session set nls_date_format='DD-MON-YYYY:HH24:MI:SS';
select sql_id, PLAN_HASH_VALUE,CHILD_NUMBER,LOADS,USERS_EXECUTING,FIRST_LOAD_TIME,LAST_ACTIVE_TIME, OPEN_VERSIONS from v$sql where sql_text like 'select * from x%';
pause
-- Now we go back to the first user and execute the query again. Notice that the last_active_time is updated again
conn test1/test
select * from x where x='Y';
SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR);
alter session set nls_date_format='DD-MON-YYYY:HH24:MI:SS';
select sql_id, PLAN_HASH_VALUE,CHILD_NUMBER,LOADS,USERS_EXECUTING,FIRST_LOAD_TIME,LAST_ACTIVE_TIME, OPEN_VERSIONS from v$sql where sql_text like 'select * from x%';