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The new trend has been demanding real-time data from the data warehouse.

    Ask The Experts published in
July 8, 2004
  By Sid Adelman and Chuck Kelley and Les Barbusinski


The new trend has been demanding real-time data from the data warehouse: 1) to generate operational report at high frequency 2) to provide a golden source (real-time reference data) for multiple OLTP Applications. Which is the right ETL tool to extract data from multiple OLTP sources with no latency and importantly no performance impact on OLTP. RDBMSs are Informix, Oracle and DB2 UDB?


Sid Adelman's Answer: To those of you who believe that the support garment industry can produce pantyhose in a one-size-fits-all package, a real-time data warehouse might be appealing but you will deliver a compromise that is sometimes baggy and sometimes stretched to the breaking point. Analysts and knowledge workers need a stable source of data. When they run a query and run it again 10 minutes later, they want the results to be the same. Go back to the basics and learn the purpose of a data warehouse and don't let the current trend push you into a foolish implementation.

Chuck Kelley's Answer:In a word, "never." There will always be some degradation or latency. But most likely both will occur.

Les Barbusinski's Answer: Both Informatica and Ascential offer real-time/zero latency ETL engines that work with a variety of relational databases and packaged applications (e.g., ERP, SCM, CRM, etc.). How much of an impact these have on the OLTP environment depends on the implementation.

The only other near real-time ETL option I've seen is to use database replication to create a copy of the operational database on a separate server, and have an ETL tool monitor that replicated copy for changes that need to be posted to the data warehouse. Obviously, this method introduces latency factors that can make the data several minutes old before it gets into the data warehouse, but it has the benefit of having near-zero impact on the OLTP environment. Hope this helps.


Sid Adelman is a principal in Sid Adelman & Associates, an organization specializing in planning and implementing data warehouses and in establishing effective data architectures and strategies. He jointly developed a methodology, MapXpert for Data Warehouse, that provides a master plan for implementing a data warehouse. Adelman is a regular speaker at The Data Warehouse Institute and IBM's DB2 and Data Warehouse Conference. He chairs the "Ask the Experts" column on and is a founding member of the Business Intelligence Alliance. Adelman is a frequent contributor to journals that focus on the data warehouse. He coauthored Data Warehouse Project Management with Larissa Moss and Impossible Data Warehouse Situations: Solutions from the Experts. He can be reached at (818) 783-9634 or Visit his Web site at

Chuck Kelley is a senior advisory consultant for Navigator Systems (, an independent consulting firm fully focused on corporate performance management (CPM) and BI solutions. Kelley is an internationally known expert in database and data warehousing technology. He has more than 25 years of experience in designing and implementing operational/production systems and data warehouses. Kelley has worked in some facet of the design and implementation phase of more than 45 data warehouses and data marts. He also teaches seminars, coauthored three books on data warehousing and has been published in many trade magazines on database technology, data warehousing and enterprise data strategies. He can be contacted at

Les Barbusinski is vice president of technology and co-founder of Digital Symmetry, LLC, a consulting firm that specializes in the design and development of data warehousing and business intelligence solutions. He has more than 20 years of experience in data warehouse and operational systems development and provides hands-on expertise in data warehouse design, development and project management. Les can be reached at

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