Replication :: Alternative For Complete Refresh / Delete Records From MVIEWS?

TABLE NAME :ABC
(PARTITION BASE TABLE - 84 Partition and each Partition has 500-800 Millions of Records)

/* Step1 Create MATERIALIZED VIEW LOG */
CREATE MATERIALIZED VIEW LOG ON ABC;

/* Step2 Create MATERIALIZED VIEW Refresh after Every 20 Minutes */
CREATE MATERIALIZED VIEW MV_ABC
REFRESH FAST
START WITH SYSDATE
NEXT SYSDATE+20/ (24*60) AS
SELECT * FROM ABC
WHERE TMSTP > SYSDATE-1;

Scenario:Intially data extracted will be "Greater than SYSDATE-1 = 18/08/2009 11:27:39 " - 76 Millions of Records After 20 Min of FAST Refresh, it will add 2500 Records

i)Is query in the MVIEWS (MV_ABC) SYSDATE-1 will be changed on each FAST Refresh, as observation (as per definition) it is incrementing the records to intial extracted data?

ii)As COMPLETE Refresh will be expensive to execute on the partition base table on each refresh.
Is there any alternative way to achieve the Nature of COMPLETE REFRESH in Materialized View?

iii)Is Delete or Conditional Delete option is possible in Materialized View (i.e not a delete from the base table but the delete from MVIEWS)?

iv)What is the machnism for populating the logs for MVIEWS?Is it overhead for the system and better than a Trigger based approach?