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Don Burleson Blog 







Over-allocation of Oracle resources

Oracle Database Tips by Donald BurlesonMarch 3,  2015

WIP - Not ready to publish

Too much of a good thing?

Ever since Oracle was invented, DBA's have struggled to optimizer the database to his environment.  You need to give Oracle enough resources without over-allocating precious server and internal resources.  Even at the design level we have the problem of over-normalization.


While it was appropriate back in the 1990's to design all databases in 3NF (Third Normal Forms, without redundancy), the falling costs of disk has made the re-introduction of redundancy important.  Today, Oracle shops design their tables in 3NF (or BCNF), and then deliberately introduce redundancy into the model (via the definition of materialized views to "pre-join" tables and standard denormalization).

This choice of adding redundancy depends on the redundancy boundary, a design note that all Oracle professionals should embrace.  At the heart of the matter, there is a trade-off between redundancy (extra disk) and improved performance (by doing less table joins).

Over-Allocated Hardware

At the hardware layer, we also see over-allocation of dedicated hardware resources:

·         Over-allocated RAM

·         Over-allocated CPU

This was especially predominant during the dark-ages of client-server computing, a 20th century practice of using one tiny server for each Oracle instance.  This one-server, one-instance architecture led to huge amounts of wasted CPU and RAM, which could not be shared between servers.  We see the same issue today with VMware, whereby fencing of RAM and CPU can lead to over-allocation and waste.  For more details on this important issue, see Bert Scalzo's new book "Oracle on VMware".

But what about over-allocation with an instance?  Does Oracle have an insatiable appetite for resources, or is there a diminishing return on investment?

Even within the instance we have some over-allocation issues:

·         Over-allocated PGA

·         Over allocated shared pool

·         Over-allocated data buffer

So, what are the best practices for determining when Oracle has an optimal configuration?  Does Oracle have an insatiable appetite for RAM and CPU?  Let's take a closer look.

What is the nature of scarce resources?  There are several important points to remember.

  • Hardware depreciates rapidly, regardless of usage - It is the job of the DBA to use all of the computing resources without over-allocating them.  Under-allocation is a waste because RAM and CPU depreciate rapidly, and over-allocation causes high CPU enqueues and RAM paging.

  • Most Oracle data is unpopular - All databases have frequently-referenced data blocks (popular data), and a long tail of unpopular data.  Caching unpopular data can be a waste of expensive RAM resources.






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