RDB, Oracle 9i and Materialised Views

Hi all,
I have a RDB 7.1.5.9.1 and an Oracle 9.0.1.4.0 database and the data from the RDB has to be available for queries in Oracle Discoverer. There is a 1Gb (fixed) line between the databases. I have created a database link and that is working fine.
The RDB is used 24h a day and it is very important that there are no performance problems. I do not think that a 1-on-1 recreation of the data model of the RDB in the Oracle database (with the use of the database link) is the answer. The advantage is of course that the data is always up to date, but when multiple queries are started in Oracle Discoverer I think we have a problem. And the users are used to the fact that the data is not refreshed during the day, so that isn’t an issue.
So I was thinking of using Materialised Views. Because RDB doesn’t understand Materialised View Logs I can only do a complete refresh of these Materialised Views in Oracle. I can spread the time in which these are refreshed, but I only got about 1 hour (from 7 AM to 8 AM) to refresh about 1200Mb (that is not a lot), but in the future there will be an increase in the amount that has te be refrshed.
Does anybody know what a complete refresh will do to the performance of the RDB?
And what happens if someone is querying on a Materialised View during a refresh?
Of course, any other ideas are more then welcome. I am also considering the use of triggers in the RDB to INSERT-UPDATE-DELETE the data in Oracle and the use of LogMinor, although this last option is a tricky one because the Redo-statements contain rowid’s except from the INSERT statements.
Thanks!

in oracle9i database you can create materialized views with logs option but it works only under certain conditions. there is another option in oracle9i database of materialized views in which you can use time refresh.you specify time period after which your database refrsh automatically.
Yes freshing of materialized view cause performance cost on the server but it is only for time based refresh.as well as concern to the queries their is no problem with them when m-vies is in refresh state.oracle's own infrastructure can handel it.

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