See the oldest statistics history available
SQL> SELECT DBMS_STATS.GET_STATS_HISTORY_AVAILABILITY FROM DUAL;
GET_STATS_HISTORY_AVAILABILITY
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25-OCT-11 10.00.55.093000000 PM -07:00
See the stats retention
SQL> select dbms_stats.get_stats_history_retention from dual;
GET_STATS_HISTORY_RETENTION
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31
Modify retention
SQL> exec DBMS_STATS.ALTER_STATS_HISTORY_RETENTION(60);
Space currently used to store statistics in SYSAUX in KBytes, so increasing the retention would affect it’s size
SQL> select occupant_desc, space_usage_kbytes from v$sysaux_occupants where OCCUPANT_DESC like '%Statistics%';
OCCUPANT_DESC SPACE_USAGE_KBYTES
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Server Manageability – Optimizer Statistics History 17920