Performance issue with sys.user_history$ table

Question

Hi,
I am investigating performance for one of my client's databases (which is at 9.2.0.8) as they are experiencing intermittent poor response. In the Statspack report (Top SQL section) I can see that a catalog table called SYS.USER_HISTORY$ is being accessed very frequently. Now I understand that this would be a result of password limits being set in users' profile but each time the table is accessed, it would appear to incur a full table scan resulting in over 7,500 gets each time. The total buffer gets (and physical blocks read) from this table account for a high percentage of the total and since the highest waits are buffer and I/O related this must be a major factor. Here is an extract from the Statspack report:
CPU Elapsd
Buffer Gets Executions Gets per Exec %Total Time (s) Time (s) Hash Value
2,327,138 316 7,364.4 7.8 190.22 4889.61 3236020785
select password_date from user_history$ where user# = :1 order by password_date desc
2,320,524 313 7,413.8 7.8 199.41 4278.44 3584552880
delete from user_history$ where password_date < :1 and user# = :2
2,272,260 308 7,377.5 7.6 169.36 3453.12 822812381
select 1 from dual where exists (select password from user_history$ where password = :1 and user# = :2)
Physical Reads Executions Reads per Exec %Total Time (s) Time (s) Hash Value
1,448,689 316 4,584.5 20.6 190.22 4889.61 3236020785
select password_date from user_history$ where user# = :1 order by password_date desc
1,269,172 313 4,054.9 18.1 199.41 4278.44 3584552880
delete from user_history$ where password_date < :1 and user# = :2
1,206,906 308 3,918.5 17.2 169.36 3453.12 822812381
select 1 from dual where exists (select password from user_history$ where password = :1 and user# = :2)
Is there any way to improve access to this table? Since it's a catalog table, I presume it would not be acceptable to an index to it but, for example, would it be acceptable to assign it to a suitably sized KEEP buffer pool which should at least reduce the amount of physical I/O incurred?
Any ideas would be appreciated.
Regards,
Ian Brennan

Answer 1

Hi,
Here is the remaining information which I have now gathered:-
select count(*) from dba_users;
24681
select count(*) from sys.user_history$;
1258133
select profile, limit from dba_profiles where resource_name = 'PASSWORD_REUSE_TIME';
PROFILE LIMIT
DEFAULT UNLIMITED
PRS2_DEFAULT_PROFILE 365
select bytes from dba_segments where SEGMENT_NAME='USER_HISTORY$';
61865984
explain plan for
select password_date from user_history$ where user# = :1 order by password_date desc;
SELECT STATEMENT CHOOSE
Cost: 647 Bytes: 913 Cardinality: 83
2 SORT ORDER BY
Cost: 647 Bytes: 913 Cardinality: 83
1 TABLE ACCESS FULL SYS.USER_HISTORY$
Cost: 638 Bytes: 913 Cardinality: 83
Any further thoughts?