Never thought I would write much about Information Lifecycle Management, as I am actually a developer and not a DBA. I think, it is indeed a topic mostly relevant for DBA’s. But it is generally a good thing, if developers and DBA’s have a deep understanding of each others job, isn’t it? We are giving an overview of the ILM features in our training “12c New Features for Developers” and I’m one of the course instructors for it. That’s the reason, why I’m writing meanwhile the third post about it. Just to clarify some questions, which are not so obviously documented.
This post is again about the Slowly Changing Dimensions Type 2, but focusing on another problem. Once you have a need to validate the versioning mechanism, how you can do this? Or, in other words, having several versions of the same data (identified by the natural key), how to check what fields have been changed from version to version? Working with systems like Siebel CRM, which have some tables with 500+ columns, this possibility was really useful.
Of course you can write some PL/SQL code and iterate through the columns to compare their values. But I’m a friend of “pure SQL” solutions – let’s see how this can be done. Continue reading →
Actually, the CBO usually does a good job optimizing “NOT IN” subqueries. Unless something goes wrong. Recently it took a long time on a 10.2.0.5 database to search for the reason. At last looking in the CBO trace files (event 10053) has given the right hint. Continue reading →
It was that hint /*+ BYPASS_UJVC */ that ten years ago already taught me a lesson on how to deal with undocumented hints in productive environments. Admittedly, I still have used it since then for ad hoc data manipulation a few times. Because of a strange behavior in 11gR2 database, I decided to look again at the issue of “one-pass” updates of a join and their alternative using merge sql statement. Continue reading →
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