I am maintaining an application creating an Oracle DB via JDBC. Starting from today this query:
SELECT NULL AS pktable_cat ,
p.owner AS pktable_schem,
p.table_name AS pktable_name ,
pc.column_name AS pkcolumn_name,
NULL AS fktable_cat ,
f.owner AS fktable_schem,
f.table_name AS fktable_name ,
fc.column_name AS fkcolumn_name,
fc.position AS key_seq ,
NULL AS update_rule ,
DECODE (f.delete_rule, 'CASCADE', 0, 'SET NULL', 2, 1) AS delete_rule ,
f.constraint_name AS fk_name ,
p.constraint_name AS pk_name ,
DECODE(f.deferrable, 'DEFERRABLE',5 ,'NOT DEFERRABLE',7 , 'DEFERRED', 6 ) deferrability
FROM all_cons_columns pc,
all_constraints p ,
all_cons_columns fc,
all_constraints f
WHERE 1 = 1
AND p.table_name = :1
AND p.owner = :3
AND f.constraint_type = 'R'
AND p.owner = f.r_owner
AND p.constraint_name = f.r_constraint_name
AND p.constraint_type = 'P'
AND pc.owner = p.owner
AND pc.constraint_name = p.constraint_name
AND pc.table_name = p.table_name
AND fc.owner = f.owner
AND fc.constraint_name = f.constraint_name
AND fc.table_name = f.table_name
AND fc.position = pc.position
ORDER BY fktable_schem,
fktable_name ,
key_seq
started becoming really slow due to some oracle internals as it seems to be the same for all my branches.
Does somebody know one possible reason and how to face this?
Regards, Nunzio
Data dictionary or fixed object statistics might be old, try re-gathering them:
exec dbms_stats.gather_dictionary_stats;
exec dbms_stats.gather_fixed_objects_stats;
alter system flush shared_pool;
Even that does not necessarily gather statistics for all system objects. Some objects, like X$KFTBUE, must be gathered manually. Although that's a rare data dictionary problem that may not be relevant here.
If that doesn't work some next possible steps are looking at tools like SQL Tuning Advisor to create a profile, or using SQL Plan Management to force the optimizer to use a specific plan that has worked before. Tuning a data dictionary query can be very difficult since you don't have much control.