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April 2009

Dynamic logging with global application context

Controlling logging output across sessions using global application context. September 2007 (updated April 2009)

Collaborate 09: Don’t miss these sessions

Collaborate 09 starts on Sunday, May 3 (a few days from now!) in Orlando. I’ve been offline for several weeks (more on that later), but will be returning to the world of computers and technology in full force in Orlando. I’ve had a few inquiries about whether or not I’ll be at Collaborate, so I thought I’d resurrect my blog with a post about where I’ll be and some of the highlights I see at Collaborate 09.

First, where I’ll be presenting:

The Most Common Performance Problem I See

At the Percona Performance Conference in Santa Clara this week, the first question an audience member asked our panel was, "What is the most common performance problem you see in the field?"

I figured, being an Oracle guy at a MySQL conference, this might be my only chance to answer something, so I went for the mic. Here is my answer.

The most common performance problem I see is people who think there's a most-common performance problem that they should be looking for, instead of measuring to find out what their actual performance problem actually is.

It's a meta answer, but it's a meta problem. The biggest performance problems I see, and the ones I see most often, are not problems with machines or software. They're problems with people who don't have a reliable process of identifying the right thing to work on in the first place.

That's why the definition of Method R doesn't mention Oracle, or databases, or even computers. It's why Optimizing Oracle Performance spends the first 69 pages talking about red rocks and informed consent and Eli Goldratt instead of Oracle, or databases, or even computers.

Understanding the different modes of System Statistics aka. CPU Costing and the effects of multiple blocksizes - part 1

Forward to part 2

This is the first part of a series of posts that cover one of the fundamentals of the cost based optimizer in 9i and later. Understanding how the different system statistics modes work is crucial in making the most out of the cost based optimizer, therefore I'll attempt to provide some detailed explanations and samples about the formulas and arithmetics used. Finally I'll show (again) that using multiple block sizes for "tuning" purposes is a bad idea in general, along with detailed examples why I think this is so.

One of the deficiencies of the traditional I/O based costing was that it simply counted the number of I/O requests making no differentation between single-block I/O and multi-block I/O.

System statistics were introduced in Oracle 9i to allow the cost based optimizer to take into account that single-block I/Os and multi-block I/Os should be treated differently in terms of costing and to include a CPU component in the cost calculation.

The system statistics tell the cost based optimizer (CBO) among other things the time it takes to perform a single block read request and a multi-block read request. Given this information the optimizer ought to be able to come to estimates that better fit the particular environment where the database is running on and additionally use an appropriate costing for multi-block read requests that usually take longer than single block read requests. Given the information about the time it takes to perform the read requests the cost calculated can be turned into a time estimate.

The cost calculated with system statistics is still expressed in the same units as with traditional I/O based costing, which is in units of single-block read requests.

Unloading data using external tables in 10g

External tables can write as well as read in 10g. May 2005

Helsinki code layers in the DBMS

Ok, let's continue with the second part of "The Helsinki Declaration". That would be the part where I zoom in on the DBMS and show you how best to do this database centric thing.We have seen that the DBMS is the most stable component in everybodies technology landscape. We have also concluded that the DBMS has been designed to handle WoD application BL-code and DL-code. And current DBMS's are

Tracing Oracle SQL plan execution with DTrace

SQL is a declarative language – in other words you just declare what needs to be done and Oracle takes care of the part how it’s done.

However there’s nothing declarative about the actual SQL execution when it happens. SQL plan is just a tree of kernel rowsource functions executed in a specific order (defined in child cursor’s sql area).

The root of SQL plan is where the fetch function (opifch2 for example) gets the rows for passing back to the user (or PL/SQL engine).

The branches are operations like joins, union etc, which don’t have access to any data themselves and can just call other functions recursively to get rows

The leaves are the execution plan operations without any children, they call data layer to acces actual datablocks.

The first execution plan line (with lowest ID) without any children is the one where data access starts, that’s the place where first logical IO happens.

Seminar feedback and pictures from Singapore

I’ve been busy with a series of seminars, so haven’t managed to blog much…
Karl Arao has posted some feedback from my Singapore seminar and also the pictures we took with attendees. By the way, he has other good Oracle stuff in his blog so check it out here.

Advanced Oracle Troubleshooting by Tanel Poder in Singapore

When I first saw that Tanel will conduct his seminar in Singapore, I told myself that I would even spend my own money just to be on that training! I’ve already read performance books like Optimizing Oracle Performance, Oracle 8i Internal Services, Forecasting Oracle Performance… And after that I still want more, and I still have questions that need to be answered. Well, if you’re on a tight budget you just opt to download some more docs/books to do multiple reads coupled with research/test cases and also reading through others blog…
But thanks to my boss for the funding, I was there! </p />

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Oracle ACE

I've recently been invited by Oracle to accept the Oracle ACE award.

So I'm now an Oracle ACE. You can check my Oracle ACE profile here.

Thanks to Oracle ACE H.Tonguç Yılmaz and special thanks to Oracle ACE Dion Cho, who nominated me for the Oracle ACE award.

Some statistics (since I'm a CBO guy :-):

- I'm truly honored to be Oracle ACE no. 210 in the world
- There are at present 57 Oracle ACEs in the "Database Management & Performance" category (53 in "Database App Development" and 10 in "Business Intelligence")
- There are 7 ACEs from Germany at present