I tried to build a small example here;
http://tonguc.yilmaz.googlepages.com/dbms_stats_cascade_needed.txt

Coskan hi, when to gather statistics is a very challenging question especially after 10g RBO is obsolute. Here in my company DBA prefer to use DBMS_STATS’s STALE(10% changed) statistic option. But a research on asktom and lewis’s blog could be usefull of course :)

Hakki hi, after 10g there is a job scheduled for this purpose;

SELECT owner, job_name, enabled
FROM dba_scheduler_jobs
WHERE job_name = ‘GATHER_STATS_JOB’

This job is needed because RBO is dead, and your index will be analyzed when this job starts at its scheduled time if it is in STALE status. Also new created segments without statistics will be gathered.

Çok yogun insert ler yaptıktan sonra baktım, analiz tarihi oluşturuldugu andaki tarih ve num_rows alanı yine ilk andaki ile aynı..Ne zamanki analyze index komutu verdim, bilgiler güncellendi.

For gathering stats There is an explanation of WHY, Is there an exact explanation about WHEN ?

We have to collect statistics for CBO to make the right decision of access paths.

But when it is necessary ?

In my way; I query the table ALL_TAB_MODIFICATIONS for gathering the change on data and make the decision from the result set. (If there is a change of 10 percent for insert update and delete i gather the stats of index and table). This table is very useful for understanding what is happening to my data ?. This table is started to be populated after the last statistics collection and holds all the change on the table.

like the query below

select dt.table_name,dt.owner,num_rows from all_TAB_MODIFICATIONS tb,dba_tables dt where
dt.TABLE_NAME=tb.TABLE_NAME
and (dt.num_rows*10/100

Patrick