Question :
How to tune the following query, as it’s taking around 8 seconds:
select constraint_name,table_name
from all_constraints
where r_constraint_name in
(select constraint_name
from all_constraints
where table_name='SUPPLIER');
SUPPLIER is an example table name.
Answer :
Often the RULE-hint helps when querying dictionary views.
select /*+ RULE */ constraint_name,table_name
from all_constraints
where r_constraint_name in
(select constraint_name
from all_constraints
where table_name='SUPPLIER');
But your query is not precise. Objects have an owner, too.
select /*+ RULE */ owner, constraint_name,table_name
from all_constraints
where (r_owner, r_constraint_name) in
(select owner,constraint_name
from all_constraints
where table_name='SUPPLIER'
and owner='SOMEONE');
But this query can be formulated as a join.
select /*+ RULE +*/ ref.owner, ref.constraint_name,ref.table_name
from all_constraints ref, all_constraints cons
where ref.r_constraint_name=cons.constraint_name
and ref.r_owner=cons.owner
and cons.owner='&OWNER'
and cons.table_name='&TABLE';
If you prefer the modern JOIN syntax
select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
from all_constraints ref JOIN all_constraints cons
on (ref.r_owner=cons.owner and ref.r_constraint_name=cons.constraint_name)
where
cons.owner='&OWNER'
and cons.table_name='&TABLE';
here are some timing results, with and without RULE hint on a 12c database (12.1.0.2.0)
SQL> alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.44
SQL> select ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:03.95
SQL> select ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:00.00
SQL> alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.02
SQL> select ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:03.94
SQL> alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.01
SQL> select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:00.27
SQL> select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:00.16
I also gathered statistics on the SYS objects using
SQL> exec dbms_stats.gather_schema_stats('SYS',options=>'GATHER', -
> estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE, -
> method_opt => 'FOR ALL COLUMNS SIZE AUTO', cascade => TRUE);
PL/SQL procedure successfully completed.
Elapsed: 00:03:41.58
but that didn’t help.
On 11g systems (11.2.0.4.0) the query without hint performs far better, but even there the hint accelerates the query
SQL> alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.01
SQL> select ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:00.65
SQL> alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.01
SQL> select ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:00.66
SQL> alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.01
SQL> select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
2 from all_constraints ref, all_constraints cons
3 where ref.r_constraint_name=cons.constraint_name
4 and ref.r_owner=cons.owner
5 and cons.owner='OWNER'
6 and cons.table_name='TABLE';
no rows selected
Elapsed: 00:00:00.18
SQL>