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March 2013

STDDEV: Standing Sentinel on Your Data

Oracle Database implements a family of STDDEV functions for computing the
standard deviation from the mean. If you think of the mean as beginning to
paint a picture of the underlying data, then...

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AMIS Masterclass – Two Day Masterclass with Oracle ACE Director James Morle

AMIS is spending a lot of effort keeping our people up-to-date with the latest knowledge needed to help our customers the best way we can. Traditionally we also always try to share our knowledge with customers and others, via social media or conferences, and while abroad learning from others at the same time. It is …

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VirtualBox 4.2.10…

Were you thinking, “I’ve got nothing better to do this weekend than to download the latest version of VirtualBox and update the guest additions on all my VMs”? Well your luck is in!

Oracle have just released VirtualBox 4.2.10. The downloads and changelog are in the usual places.

Happy upgrading!



Premature Optimization

Premature optimization, (probably) because of Donald Knuth’s famous line “premature optimization is the root of all evil,” (see Structured Programming with go to Statements) is, at the very least, a controversial topic. The misconception based on that particular quote is that a programmer, while writing code, should ignore optimization altogether. In my opinion this is wrong. To put the quote in context, let’s have a look to at the text that precedes and follows it:

The problem with free and RSS…

The internet has been awash with people bemoaning the decision by Google to close Google Reader. Probably the next biggest talking point has been people asking what they can use to replace it when it’s gone. I’m planning on giving a test-drive, once I can get my feeds imported. :)

The problem with free

UltraEdit v19 for Windows

For all those folks who are forced to use Windows, you might be interested to know UltraEdit v19 has just been released.

You can check out the new features here.

The latest version for Mac/Linux is still 3.3, so maybe we are due a new version there too?



Enkitec’s Exadata Smart Flash Cache Hacking Session by Tanel Poder! (free stuff!!!)

We recently received our 3rd Exadata machine into Enkitec’s exalab. Now we have a V2, X2 and X3 there, in addition to ODA, Big Data Appliance (which comes with a beer-holder built in!) and an Exalytics box! So you understand why Karl Arao is so excited about it :-)

This occasion demands that we hack the hell out of all this kit soon! So, let’s have another (super-secret) hacking session!

This time, let’s see how the Exadata Smart Flash Cache works! (both for reads and writes). Note that we won’t cover Smart Flash Logging in this session (otherwise we’ll end up spending half a day on it :)

Parallel unfriendly

Take a look at the following Parallel section of a SQL Monitor report:

Any query which produces such a report won't care about how much parallel you're running because virtually all the time is spent by the query coordinator (which is a serial process) being busy.

In this case the query in question is quite simple:

select /*+ parallel(t,8) */ median(basket_amount) from whs.fact_sale t

The reason it behaves the way it does has everything to do with how Oracle executes it:

Execution Plan
Plan hash value: 712547042


Complete SAP projects in half the time : webinar

March 20, 2013, Wednesday, 10:00 am-11:30 am PST

Speaker:   Rick Caccia, Vice President Strategy at Delphix

To Register:  Click Here

Delphix accelerates SAP project delivery by eliminating redundant infrastructure and slow processes.

Delivering application projects quickly can immediately impacts revenues and earnings.  Most IT organizations can only fund a small number of projects in a given year which limits the ability of businesses to capture these market opportunities and operational efficiencies.

"Cost-free" joins - 2

In the previous post I've demonstrated an unexpected Nested Loop Join caused by an extreme data distribution. Although unexpected at first sight, the performance of the execution plan selected by the optimizer is decent - provided the estimates are in the right ballpark.Here is another case of an unexpected execution plan, this time about Merge Joins.

Merge Joins

In order to appreciate why the execution plan encountered is unexpected, first a quick summary about how Merge Joins work:A Merge Join is essentially a Nested Loop operation from one sorted row source into another sorted row source.