Automatic statistics generation in 11.2

Question

Dear experts!
I've initialized the automatic statistics collector in my 11.2 db as follows:
BEGIN
DBMS_AUTO_TASK_ADMIN.ENABLE(
client_name => 'auto optimizer stats collection',
operation => NULL,
window_name => NULL);
DBMS_SCHEDULER.SET_ATTRIBUTE('SYS.MONDAY_WINDOW', 'repeat_interval', 'freq=daily;byday=MON;byhour=11;byminute=0;bysecond=0');
DBMS_SCHEDULER.SET_ATTRIBUTE('SYS.WEDNESDAY_WINDOW', 'repeat_interval', 'freq=daily;byday=WED;byhour=11;byminute=0;bysecond=0');
DBMS_SCHEDULER.SET_ATTRIBUTE('SYS.FRIDAY_WINDOW', 'repeat_interval', 'freq=daily;byday=FRI;byhour=11;byminute=0;bysecond=0');
DBMS_SCHEDULER.SET_ATTRIBUTE('SYS.THURSDAY_WINDOW', 'repeat_interval', 'freq=daily;byday=THU;byhour=11;byminute=0;bysecond=0');
DBMS_SCHEDULER.SET_ATTRIBUTE('SYS.TUESDAY_WINDOW', 'repeat_interval', 'freq=daily;byday=TUE;byhour=11;byminute=0;bysecond=0');
DBMS_STATS.GATHER_SCHEMA_STATS(ownname => 'DBUSER',
options => 'GATHER AUTO',
estimate_percent => dbms_stats.auto_sample_size
END;
After this initial procedure the automatic maintenance task checks from monday to friday at 11 am if the statistics of the database objects are still ok. For objects with old statistics they are newly generated.
The first question is with which parameters the automatic maintenance task executes the dbms_stats.gather_... for the objects with old statistics. In my opinion it'll take the same options as specified in the initial procedure (options=GATHER AUTO and estimate_percent=dbms_stats.auto_sample_size). Am I right?
The second question belongs also to the parameter of the dmbs_stats procedure - but in another context:
Some used tools generate statistics too after intensive workload, they execute the following:
execute DBMS_STATS.GATHER_SCHEMA_STATS(ownname => 'DBUSER',
options => 'GATHER EMPTY',
estimate_percent => 70
execute DBMS_STATS.GATHER_SCHEMA_STATS(ownname => 'DBUSER',
options => 'GATHER STALE',
estimate_percent => 70
So what happens to my automatic maintenance task after these two procedure calls? Do these two procedures overwrite the inital provided option (GATHER AUTO) which is required for automatic statistics collection? If yes does it mean that the automatic statistics collector doesn't maintain the database objects any more?
Thanks for your help!
Best regards!
Markus

Answer 1

1. There is a database and table option called MONITORING. By default this is turned on from 10g. So database is watching for changes and will collect statistics on tables/objects where needed in GATHER AUTO option.
2. No GATHER AUTO options wont be touched but you recollect stats on objects you specified in function/procedure call. And if those objects wont change in the future AUTO GATHER may wont touch these stats anymore....
This is a doc reference list I created when I was working on similar issue. :)
Best Practices for automatic statistics collection on Oracle 10g [ID 377152.1]
https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&doctype=BULLETIN&id=377152.1
How to check what automatic statistics collection is scheduled on 10g [ID 377143.1]
https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&id=377143.1
How To Extend Maintenance Windows For GATHER_STATS_JOB for More Than 8 Hours? [ID 368475.1]
https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&id=368475.1
Oracle 10g PL/SQL Packages and Types Reference - DBMS_SCHEDULER documentation
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14258/d_sched.htm#CIHHBGGI
Oracle 10g PL/SQL Packages and Types Reference - DBMS_STATS documentation
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14258/d_stats.htm#CIHBIEII
Oracle® Database Performance Tuning Guide 10g Release 2 (10.2) 14 Managing Optimizer Statistics 14.2 Automatic Statistics Gathering
http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/stats.htm#i41282
Statistics Best Practices: How to Backup and Restore Statistics [ID 464939.1]
https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&id=464939.1
Managing CBO Stats during an upgrade to 10g or 11g [ID 465787.1]
https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&doctype=HOWTO&id=465787.1