Indexes in Oracle DB part 2

Submitted by epilecki on Tue, 09/09/2014 - 09:30

In my first post about indexes I promised that more in this topic will follow up and here it is... This series of articles is based on observation how developers fail to correctly implement indexing in their applications based on Oracle and aims to provide guidelines on how indexes should be used. Today let’s focus on index scans. Understanding how their work might be very helpful in planning the indexing strategy!

Backups in Data Guard environment

Submitted by sskorupi on Fri, 09/05/2014 - 12:36

Physical standby databases seem to be ideal candidates for offloading backups from primary ones. Instead of "wasting" resources (unless you're already using Active Data Guard for example), you could avoid affecting primary performance while backing up your database, especially if your storage is under heavy load even during normal (user- or application-generated) workload. So, if you're seeking for good reasons to convince your boss/finance department/etc.

Scaling up Cardinality Estimates in

Submitted by canali on Tue, 08/05/2014 - 14:03

Topic: Counting the number of distinct values (NDV) for a table column has important applications in the database domain, ranging from query optimization to optimizing reports for large data warehouses. However the legacy SQL method of using SELECT COUNT (DISTINCT <COL>) can be very slow. This is a well known problem and Oracle provides a new function APPROX_COUNT_DISTINCT implemented with a new-generation algorithm to address this issue by providing fast and scalable cardinality estimates.



Unified auditing performance

Submitted by sskorupi on Wed, 06/25/2014 - 15:35

In my previous blog post ( I provided you with number of reasons why unified auditing looks very promising and should be seriously considered while migrating to 12c. Nonetheless, I was not talking at all about performance – which also seems to be greatly improved.

Indexes in Oracle DB part 1

Submitted by epilecki on Fri, 06/06/2014 - 09:16

Indexes… what indexes?

Indexes are one of the key Oracle features in terms of improving query performance and one might think it should be clear to everybody when and how to use them. Not at all... Working as a DBA for several years I was surprised to notice that so many developers do not know what indexes are, how they work and how to use them efficiently. I thought it would be good to put this knowledge down in a series of blog posts… and here we are!  Let’s start with…

Starting workload capture hangs - is it really problem with RAT?

Submitted by sskorupi on Tue, 06/03/2014 - 08:40

If you plan to introduce changes in your environment and want to estimate their impact, Real Application Testing feature seems to be one of the best options. As we needed to check the influence of changes planned in our databases, I've started to look for good candidates to capture the workloads. I wanted to capture only workloads associated with small number of schemas, but from several databases, to be able to properly simulate as much types of production workloads existing in our databases as possible.


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