about DBA_HIST_SEG_STAT

DBA_HIST_SEG_STAT displays historical information about segment-level statistics. This view captures the top segments based on a set of criteria and captures information from V$SEGSTAT. The total value is the value of the statistics since instance startup. The delta value is the value of the statistics from the BEGIN_INTERVAL_TIME to the END_INTERVAL_TIME in the DBA_HIST_SNAPSHOT view.

The DML counters from this view represent the number of DML operations since the last gather statistics.
The overhead on performance is not to be considerable since this mechanism work on memory and flush changes to DBA_TAB_MODOFICATIONS view periodically.

In 9i, tables should be implemented with monitoring by executing "alter table ... monitoring", but in 10g monitor is enabled by default.

The advantage of this feature is when gathering statistics.
Based on the dba_tab_modifications view we can gather statistics for only tables that have more than X% changes (compared to num_rows in user_tables) since last gather statistics.


exec dbms_stats.flush_database_monitoring_info; to refresh the view.