Mview log is needed for mview fast refresh.It records
every changed row.But for Partition Maintenance Operations (PMOPS) such
as alter partition, drop partition, truncate partition, etc, the mview
log does't record these information.In order to keep the materialized
view consistence with master table(or base table) and avoid complete
refresh,since Oracle server version 9i,Oracle can take advantage of PCT
(Partition Change Tracking) mechanism to do a fast_pct refresh.
Although fast_pct refresh will not refresh all rows of a table,it will
refresh all rows related to the changed partitions.
But there are some limitations of fast_pct.PCT is not
supported over database links.If the materialized view is distributed
(i.e. the master table and the materialized view are located on
different databases) then an ORA-12034( Materialized View Log Younger
than Last Refresh) error is expected after PMOPS to force a complete
refresh. Another limitation is the top level partition key must consist
of only a single column.
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