What is a "fast refresh" of materialized views?

A FAST REFRESH of a materialized view applies only changed data to the materialized view. This way you don't have to rebuild the materialized view every time data in the base tables' change. Oracle keeps a log of changed data in a different object called a materialized view log.

To indicate a FAST REFRESH, use the following syntax:

CREATE MATERIALIZED VIEW SEQ_AGGR_INFO
REFRESH FAST ON COMMIT | ON DEMAND | ON STATEMENT | START WITH SYSDATE NEXT SYSDATE+1/24/60
ENABLE QUERY REWRITE
AS
select RDATE, count(SEQNO) as antall, max(SEQNO) as makssekvens
from DATE_TO_SEQNO
group by dato
order by 1, 2;

ON COMMIT instructs oracle to refresh the materialized view whenever a transaction against the master table commits.

ON DEMAND instructs oracle that the materialized view should not be refreshed unless the user manually executes one of the DBMS_MVIEW refresh procedures.

ON STATEMENT instructs oracle to automatically refresh refresh the materialized view every time a DML operation is performed on any of the materialized view's base tables.

START WITH specifies a datetime expression for the first automatic refresh time. NEXT indicates the interval between automatic refreshes

General restrictions for FAST REFRESH are listed here