Track changes in Materialized view.

Question

Hi all,
i would like to know if it is possibile to track changes in a Materialized view.
1) i have a materialized view tha can be fast refreshed, built on remote tables
2) base tables have, on remote DB, Materialized view log with rowid and primary key
3) Changes in the base tables are not frequent so the refresh of my mv is very fast even if master tables have millions of records.
I would like to know if it is possibile to insert into my materialized view the date of the refresh of the single record. In this way i can read only data that have changed in my MV. The problem is that even if only one row has changed i have to read all the data from my mview.
thanks
Fra
Edited by: 859718 on 24-mag-2011 0.08

Answer 1

Hi,
firstly I must say - it's silly to refuse materialized view log. The impact of this solution is minimal and it's standard and reliable. Then you can use fast refresh and that is certaily the best for both - master and MV side. The MV log is just a table, where trigger stores rowid of changed rows. There are not other solution, bacause you need to do the same things as MV log funcionality.
If you cannot make changes to the remote database, I see only one (but unreliable solution) - use the flashback query. Then you will be able to see row changes for some period in past. The information is read from undo tablespace so that the period length depends on remote database workload. It's risky to rely on information from UNDO tablespace, but you can write your own refresh with some special fucionailty - if flashback query returns the desired changes, refresh only changed rows, otherwise do complete refresh.
SELECT
    ROWID,
    VERSIONS_STARTSCN,
    VERSIONS_ENDSCN,
    VERSIONS_OPERATION,
    t.*
FROM master_table versions between timestamp minvalue and maxvalue t
where VERSIONS_STARTSCN is not null;Columns description is for example here:
http://www.oracle-developer.net/display.php?id=320
And if you wrote your own custom refresh function you could add the timestamp functionality too :-)