RE: Flashback query to ensure data consistency

From: Ken Naim <>
Date: Wed, 26 Mar 2008 21:19:38 -0400
Message-ID: <F1143B57B1D64C9495584693A4269DEB@KenPC>

If you are using type 2 dimensions then run each query as of last night and you don't have to worry about the newly loaded data.  


From: [] On Behalf Of Tony Aponte
Sent: Wednesday, March 26, 2008 6:15 PM
To:; Subject: RE: Flashback query to ensure data consistency  

The first thing I would say to you is to try the flashback/trigger strategy you've worked out and see how it affects the user queries. I have flashed back up to 10 days and still met query requirements.  

Another approach is the Kimball real-time data warehouse strategy that Dennis Williams already suggested.  

A third approach I would pursue is to use Analytic Workspaces. With that you can redirect the burden to the ETL workload instead and relieve the queries from having to indo the transactions. At the end of the ETL processing you would use the Workspace features to merge the changes that have been made to the base tables.  

Another approach could be to use Materialized Views and Query Rewrite against the base tables. This would give you control over when to publish the ETL updates by simply refreshing the MVs after the 8-hour jobs are complete, yet still provide a consistent view of the previous data.  

Tony Aponte  

From: [] On Behalf Of Debaditya Chatterjee
Sent: Wednesday, March 26, 2008 4:42 PM
Subject: Flashback query to ensure data consistency  


In a 24*7 data warehouse (accessed by users globally from different timezones), incremental ETL jobs are executed to load data from different source systems. Due to excessive volume of source data the ETL window has grown to over 8 hours and users from a particular timezone (the most affected ones) have started complaining about performance of the system and also have become very vocal about data inconsistency. e.g. figures of a sales report can change as the ETL tool commits every 10K records.

In order to give the users a consistent view of data we are thinking of using the Flashback query feature of the database. i.e. When the ETL starts, flashback query will be enabled and the user queries (through a logon trigger) will run against the flashback data and once the ETL completes the queries will run against the tables.

Although the solution seems feasible, but having flashback to work for more than 8 hours seems to be our biggest challenge. I wanted to verify if you all agree with this approach or would you suggest using a simpler (but costly) approach like routing queries to a read only standby database while ETL jobs execute on the primary database.

Your suggestions are welcome. The oracle database version is, the ETL tool used is Informatica and the reporting tool used is Siebel Analytics.


Received on Wed Mar 26 2008 - 20:19:38 CDT

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