oracle materialized view - refesh occuring but base tables not being deleted

hi,

we have an application which uses materialized views. the refresh action (using fast refresh) executes without error but for some reason the base materialized views (<schema>.MLOG$_<table>) does not get deleted (we do a select count(1) from the base table). as i understand it the entries are supposed to be removed. a few additional peices of information:
* the base tables are only used by one materialized view.

• there have been problems with the refresh over the past few weeks failing until we increased the refesh interval (controlled by the application)
• there are over 100,000,000 entries in the base table. i'm going to be investigating this in more detail myself over the next few days and will add anything i find. g