Oracle Scratchpad

February 4, 2011

Dynamic Views

Filed under: humour — Jonathan Lewis @ 7:42 pm GMT Feb 4,2011

People forget from time to time that when you query the dynamic performance views (v$ views) you shouldn’t expect to get a read-consistent result set – and this can lead to some very strange results, especially when you start writing joins between views (for example you may be able to find a session is both “not waiting” and “waiting” if you still join v$session and v$session_wait).

Here’s a visual analogy to help you remember what’s going on: “Australian Propellors ?”

And a graphic to help explain the phenomenon: “Rolling Shutter Effect.”

And here, for stunning effect only, is another clip that appeared in the “related topics”.

August 2, 2010


Filed under: humour — Jonathan Lewis @ 6:13 pm BST Aug 2,2010

There are only three join mechanisms used by Oracle:

Here’s an important thought, though: all three join methods are nested loop joins with different startup costs.



July 21, 2010

Design …

Filed under: humour — Jonathan Lewis @ 8:38 pm BST Jul 21,2010

… and how not to do it.

In the last couple of weeks I’ve visited two offices which have some really high-tech coffee machines, both from the same company. When you use these machines you have two options, you can punch out the menu options for the drink you want, or you can punch out a “quick code” for the drink you want. In my case (coffee, milk, no sugar) the code is 018, so …

Key punches for option 1

  • coffee
  • milk
  • start

Key punches for option 2

  • Enable quick code
  • 0
  • 1
  • 8
  • start

Yes, it really does take more key strokes to use the quick code than it does to choose what you want.

In fact, checking the dozens of possible drinks combinations on the machine I decided there were probably about six options where the quick code was quicker than just punching in what you wanted, for example:

  • coffee
  • extra strength
  • milk
  • more milk
  • sugar
  • more sugar
  • start

Just keep this in mind next time you think about supplying your end users with a cute feature that’s supposed to make them happier people.

June 28, 2010

Stress Test

Filed under: humour — Jonathan Lewis @ 5:45 pm BST Jun 28,2010

Here’s something you probably don’t want to say at the start of a public presentation: “Does anyone have a laptop I could borrow for the next 90 minutes.”

I’ve just done my first ODTUG presentation – and everything I do runs under VMWare, which simply refused to start. I’m in my room now trying to fix it before tomorrow’s session. (Many thanks to James Haslam from UKOUG who happened to be in the room at the time and offered up his laptop.)

Update: Inevitably it’s now running perfectly with no intervention at all – so I have to go back downstairs and see if it breaks again.

June 25, 2010


Filed under: humour — Jonathan Lewis @ 6:57 pm BST Jun 25,2010

I wish more people were aware of problems like this:  Error found on Internet!

May 20, 2010

Philosophy – 11

Filed under: humour,Philosophy — Jonathan Lewis @ 7:02 pm BST May 20,2010

The English language is full of irregular verbs, for example:

I am hypothesising about possible explanations
You are guessing
He’s talking rubbish

Addendum: The point, of course, is that your interpretation of an individual’s words may be critically affected by who the individual is. The use of the expresssion “English irregular verb” to describe this phenomenon was current around the time that I was at University.

[The Philosophy Series]

May 15, 2010


Filed under: humour,Oracle,Performance,Troubleshooting — Jonathan Lewis @ 10:44 am BST May 15,2010

There was a news item in the UK last week about a man in Chideock, Dorset who staged a protest about the volume of heavy traffic that has to come through the village where he lives.

A pedestrian crossing has recently been installed on the road, using traffic-light control. So one morning he decided to cross the road, and then come back again, non-stop, for an hour. Each time he got across the road he pressed the crossing control button to come back. A few vehicles got through on the green light each time, but after just one hour he had caused a four mile tailback of traffic.

Let this be a lesson to Oracle DBAs and developers – even a small job, if repeated very frequently, can create havoc with your system.

April 12, 2010


Filed under: humour — Jonathan Lewis @ 11:32 am BST Apr 12,2010

Browsing around the internet recently I came across this result:

“During February, 2010, was positioned by as the 33 most visited website in the United States. In order to be ranked in traffic in number 33, had 25,165,482 visits.”

Pretty impressive, isn’t it.

On the other hand, WordPress tells me that I got just 45,000 visits in Feb – so which one do I want to believe ? And how did the other one get a result that was so far out ?

March 19, 2010

Something Changed

Filed under: humour — Jonathan Lewis @ 9:50 pm GMT Mar 19,2010

I’ve been a bit busy over the last few days and haven’t had much time to do any new postings or catch up with comments; but I’ve just got a few moments to let you know about a client I visited a few weeks ago who didn’t give me the usual “nothing’s changed” story.

“We’ve only changed two things,” he said, “the hardware and the software.”***

Mind you, I wasn’t sure whether the change in the network infrastructure should have counted as a third thing.

*** I think he’d read the earlier blog item.

February 16, 2010

Performance myths

Filed under: humour — Jonathan Lewis @ 6:30 pm GMT Feb 16,2010

How legends are born:

But it won’t always work:

January 1, 2010

First Principles

Filed under: humour — Jonathan Lewis @ 8:04 pm GMT Jan 1,2010

I just had to start the new year with a little humour.

September 4, 2009

Real World

Filed under: humour — Jonathan Lewis @ 6:30 pm BST Sep 4,2009

Who says that the scientific method can’t be applied to real-world problems ?

Update – in keeping with the recent “Friday night is quiz  night” pattern, here’s a quiz on the same topic. Apologies to any who feel excluded for cultural or gender reasons:

September 26, 2008

Root Cause

Filed under: humour,Infrastructure,Troubleshooting — Jonathan Lewis @ 5:43 pm BST Sep 26,2008

There are a few expressions in the industry that irritate me – not necessarily for good reason but simply because they sound like the extremes of pretentiousness and marketing put together.  (Pretentious, moi !)

March 20, 2008


Filed under: humour — Jonathan Lewis @ 5:01 pm GMT Mar 20,2008

Tom Kyte and Pete Finnigan are both well known for talking about the need to use bind variables and the dangers of SQL Injection. This cartoon must have been written just for them.

January 2, 2007

Humour (possibly)

Filed under: humour,Non-technical — Jonathan Lewis @ 9:22 pm GMT Jan 2,2007

This may not translate well because of the colloquialisms, but it seems appropriate for the current time of year (early January) in the UK.

You may have noticed that I spend quite a lot of my time explaining why something is a bad idea and should be treated with caution. Occasionally this has resulted in complaints that I keep pouring cold water on everything. The best response to this comment is one I first heard many years ago:

“Cold water is the natural result of hot air meeting thin ice”.

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