Finding appropriate block size?

Question

Hi All,
I believe this might be basic question, How to find appropriate block size for building an database to an specific application?
I had seen always default 8K block size is used every where(Around 300-350 databases i have seen till now)....but why and how do they estimate this block size blindly before creating production database.
Also in the same way how memory settings are finalized before creating database?
-Yasser

Answer 1

Yasser,
I have been very fortunate to buy and read several very high quality Oracle books which not only correctly state the way something works, but also manage to provide a logical, reasoned explanation for why things happen as they do, when it is appropriate, and when it is not. While not the first book I read on the topic of Oracle, the book “Oracle Performance Tuning 101” by Gaja Vaidyanatha marked the start of logical reasoning in performance tuning exercises for me. A couple years later I learned that Gaja was a member of the Oaktable Network. I read the book “Expert Oracle One on One” by Tom Kyte and was impressed with the test cases presented in the book which help readers understand the logic of why Oracle behaves as it does, and I also enjoyed the performance tuning stories in the book. A couple years later I found Tom Kyte’s “Expert Oracle Database Architecture” book at a book store and bought it without a second thought; some repetition from his previous book, fewer performance tuning storing, but a lot of great, logically reasoned information. A couple years later I learned that Tom was a member of the Oaktable Network. I read the book “Optimizing Oracle Performance” by Cary Millsap, a book that once again marked a distinct turning point in the method I used for performance tuning – the logic made all of the book easy to understand. A couple years later I learned that Cary was a member of the Oaktable Network. I read the book “Cost-Based Oracle Fundamentals” by Jonathan Lewis, a book by its title seemed to be too much of a beginner’s book until I read the review by Tom Kyte. Needless to say, the book also marked a turning point in the way I approach problem solving through logical reasoning, asking and answering the question – “What is Oracle thinking”. Jonathan is a member of the Oaktable Network, a pattern is starting to develop here. At this point I started looking for anything written in book or blog form by members of the Oaktable Network. I found Richard Foote’s blog, which some how managed to make Oracle indexes interesting for me - probably through the use of logic and test cases which allowed me to reproduce what I reading about. I found Jonathan Lewis’ blog, which covers so many interesting topics about Oracle, all of which leverage logical approaches to help understanding. I also found the blogs of Kevin Closson, Greg Rahn, Tanel Poder, and a number of other members of the Oaktable Network. The draw to the performance tuning side of Oracle administration was primarily for a search for the elusive condition known as Compulsive Tuning Disorder, which was coined in the book written by Gaja. There were, of course, many other books which contributed to my knowledge – I reviewed at least 8 of the Oracle related books on the amazon.com website.
Motivation… it is interesting to read what people write about Oracle. Sometimes what is written directly contradicts what one knows about Oracle. In such cases, it may be a fun exercise to determine if what was written is correct (and why it is logically correct), or why it is wrong (and why it is logically incorrect). Take, for example, the “Top 5 Timed Events” seen in this book (no, I have not read this book, I bumped into it a couple times when performing Google searches):
http://books.google.com/books?id=bxHDtttb0ZAC&pg=PA17#v=onepage&q=&f=false
The text of the book states that the “Top 5 Timed Events” shown indicates a CPU Constrained Database (side note: if a database is a series of files stored physically on a disk, can it ever be CPU constrained?). From the “Top 5 Timed Events”, we see that there were 4,851 waits on the CPU for a total time of 4,042 seconds, and this represented 55.76% of the wait time. Someone reading the book might be left thinking one of:
* “That obviously means that the CPU is overwhelmed!”
* “Wow 4,851 wait events on the CPU, that sure is a lot!”
* “Wow wait events on the CPU, I didn’t know that was possible?”
* “Hey, something is wrong with this ‘Top 5 Timed Events’ output as Oracle never reports the number of waits on CPU.”
* “Something is really wrong with this ‘Top 5 Timed Events’ output as we do not know the number of CPUs in the server (what if there are 32 CPUs), the time range of the statics, and why the average time for a single block read is more than a second!”
A Google search then might take place to determine if anyone else reports the number of waits for the CPU in an Oracle instance:
http://www.google.com/search?num=100&q=Event+Waits+Time+CPU+time+4%2C851+4%2C042
So, it must be correct… or is it? What does the documentation show?
Another page from the same book:
http://books.google.com/books?id=bxHDtttb0ZAC&pg=PA28#v=onepage&q=&f=false
Shows the command:
alter system set optimizer_index_cost_adj=20 scope = pfile;Someone reading the book might be left thinking one of:
* That looks like an easy to implement solution.
* I thought that it was only possible to alter parameters in the spfile with an ALTER SYSTEM command, neat.
* That command will never execute, and should return an “ORA-00922: missing or invalid option” error.
* Why would the author suggest a value of 20 for OPTIMIZER_INDEX_COST_ADJ and not 1, 5, 10, 12, 50, or 100? Are there any side effects? Why isn’t the author recommending the use of system (CPU) statistics to correct the cost of full table scans?
A Google search finds this book (I have not read this book either, just bumped into it during a search) by a different author which also shows that it is possible to alter the pfile through an ALTER SYSTEM command:
http://books.google.com/books?id=ufz5-hXw2_UC&pg=PA158#v=onepage&q=&f=false
So, it must be correct… or is it? What does the documentation show?
Regarding the question of updating my knowledge, I read a lot of books on a wide range of subjects including Oracle, programming, Windows and Linux administration, ERP systems, Microsoft Exchange, telephone systems, etc. I also try to follow Oracle blogs and answer questions in this and other forums (there are a lot of very smart people out there contributing to forums, and I feel fortunate to learn from those people). As long as the book or blog offers logical reasoning, it is fairly easy to tie new material into one’s pre-existing knowledge.
Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc.