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February 2012

Testing Transport Latency

(Updated 04/04/12 to fix bug with large raw disk partitions) I need your help! One of the things that I have struggled to get data for in my storage research is the latency of the interface between server and storage device. It's easy to get numbers for the actual storage device, but the latency numbers […]

New Linux Articles…

I wrote in my New Years Resolutions post I was considering writing some revision notes for, and ultimately sitting, the RHCSA and RHCE exams.

I’ve started on that journey now with a bunch of articles.

Things that make the internet great…

Google Search Auto-complete.

Nuff said!



Stats note

This is just a temporary link to Randolf Geist’s note on a small, but potentially significant, change in the way that Oracle handles statistics when you’re fiddling with indexes and empty tables. I’ve added the link to my “bits and pieces” list (see top right) so I’ve disabled comments and will be deleting this post in a few days.

And here’s a link to a really smart piece of SQL from Timur Ahkmadeev which uses v$sysmetric to emulate the output of the statspack/AWR profile over the last few seconds. (This one’s going into the AWR/Statspack list – also in the catalogue at top right).

Interesting Index “Facts” – What is Wrong with these Quotes?

February 22, 2012 There are some amazing (or just plain interesting) facts to be found about how indexes work in Oracle Database.  One Internet site in particular that has been helpful in my understanding of Oracle indexes is Richard Foote’s blog.  I occasionally see information on the Internet, in the Oracle documentation, in Metalink (My [...]

Oracle XML Training with Marco Gralike in Ljubljana

In last two years I have been involved in many cases when we had to troubleshoot performance for processing XML files. Due to this reason I decided to organize specialized training with the best expert for processing XML in Oracle database - Marco Gralike, my fellow from OakTable and also Oracle ACE Director.
The training is organized by my company DbProf d.o.o in cooperation with Slovenian Oracle User Group - SIOUG. The training will take place in Ljubljana, March 27th and 28th 2012. More about training agenda and the pricing is available here.

SQL Quiz – How To Multiply across Rows

A colleague came to me a couple of days ago with a SQL problem. He had something like this:


NAME          INPUT
------------- -----
GROUP_1       5
GROUP_2       3
GROUP_3       4
GROUP_4       7
GROUP_5       3

What he wanted to do was multiply all the inputs across the groups, to get the total number of possible permutations. ie 5*3*4*7*3. The product of all the INPUTS. This has to be in straight SQL. Easy! You just need to… Ahhh… Hmmm…

No, I just could not think of a way to do it that my colleague could use.

Xen problems with OpenSuSE 12.1 and Intel core-i7

I have set up my new lab server yesterday, which in essence is a rack mounted server with a core i7 2600 processor, 32GB RAM and 3 TB of (slow) disk. When I moved some of my VMs across from an identical system (except that it was a core i7 920) and tried to start the domU, it repeatedly crashed. The message from the console was a simple question: is xend running?

I couldn’t believe my eyes-using identical software now produced segmentation faults? How is that possible. I am using xen 4.2, kernel 3.1.9-1.4-xen and libvirt libvirt-0.9.6-3.3.1.x86_64

I started the troubleshooting with the xen logs. There was no output in the debug log, however the xend.log showed these lines:

ACE Director Program Updates: My thoughts…

As you probably already heard, the ACE Director program has recently altered their travel assistance policy. Some of the bigger, well established events will no longer be considered for travel assistance, and even those that are will have a limit to the number of ACEs that will get funding. The immediate fallout of this is some ACE Directors (including myself) have had to pull out of some events we had planned to speak at.

My first reaction was to post the following message to Victoria, Lillian and Justin,

Thanks for the update. I hope you guys don’t get too much hassle from people about this change. If you do, just remember, people will always find something to moan about. :)

As always, I’m very grateful for all the time and effort you guys have put into the program over the years.

Not In – 2

My note on “NOT IN” subqueries is one of the most popular on my blog, staying in the top 5 hits for the last five years – but it’s getting a bit old, so it’s about time I said something new about “NOT IN” – especially since the Null Aware Anti Join has been around such a long time. The example I want to talk about is, as so often, something that came up as a problem on a customer site. Here’s a bit of SQL to model the situation, which is currently running under Oracle