Oracle Scratchpad

December 22, 2014


Filed under: Non-technical — Jonathan Lewis @ 5:28 pm GMT Dec 22,2014

I received an email a few weeks ago asking me if I would look at a series of three posts on adaptive dynamic sampling in 12c – (part 1, part 2, part 3). I took a note of the topic and URLs, and read through them fairly rapidly, and they seemed to be perfectly reasonable articles describing the authors thoughts, tests, and observations. Inevitably, though, several questions ran through my mind as I read – typically along the lines of “what would happen if …”, “did you restart the instance before …”, “did you flush the shared pool between …”. It’s very hard to create, run, and report a set of tests that allow you to make solid inferences about how Oracle and the optimizer behave – and whatever you do someone else will find a way of asking some questions that push the envelope a little further.

I got a follow-up email a week or so later, asking if I’d had time to look at the article because the author wanted to present the topic at a local (Azerbaijan) user group event – and the follow-up email prompted me to write this blog note.

Given that it’s taken about three weeks for me to get around to writing this note you might appreciate that I don’t have a lot of time to spare on a topic that I’m not actively pursuing for a good reason. I accumulate a lot of information from around the internet, from books, and from presentations, and I’ll invariably attach lots of questions and conjectures to that information but I won’t necessarily be able to have any confidence in its utility or correctness. When I have to know an answer I may go back to a source I’ve noted and use it as a basis for doing some further goal-oriented investigations – but until I need to (or unless I’m particularly curious) I don’t have the time to do arbitrary research. This means, of course, that I don’t have time to get into a dialogue with people about the work they have done and the information they have presented.

On the other hand, of course, I thoroughly approve of anyone who takes the time to do the experiment and write up the results. And I heartily approve of anyone who is prepared to stand up in front of a user group and share their observations and want to encourage people to do this; so this is the reply I sent which, I hope, is suitable positive:

There are a number of questions that I would probably want answered if I were to examine the posts in detail, and I would want to repeat the tests that you have done to check that I got the same results and to see if there were other observations I could make that might lead me to different conclusions. This is something that takes far too much time to do properly, and I have no inside information that would allow me to say very quickly whether your comments are right, wrong, or simply incomplete.

The important point, though, is that you have set up some tests, documented the results, and offered some conclusions. That is sufficient for your presentation to the user group.
  • This is what I did
  • This is what I observed
  • This is what I concluded
 At worst someone will ask some questions like: “Did you check …”, or “What happens if …”
You may need to answer “I don’t know”, or “I didn’t think of doing that”, or “That’s a good idea, I’ll try it”; but whatever happens everyone learns something, and everyone has the opportunity to learn more based on what you have given them.
In passing, at the very first presentation I did for the UK Oracle User Group about 25 years ago I got about half way through some comments on an odd performance pattern I had observed when modifying the SQL*Plus arraysize when someone stuck up their hand and asked: “Did you check the tcp packet size?” The only response I could make, after a few seconds pause to think, was: “I should have thought of that. No.”

August 6, 2013


Filed under: Non-technical — Jonathan Lewis @ 6:59 am GMT Aug 6,2013

The interview I did with Timur Akhmadeev while visiting Moscow is now online. 90 minutes ! I’ve just got through the first 6 minutes and haven’t embarrassed myself yet:

If you haven’t got the time to listen to the recording, there’s now a transcript online.

July 4, 2013


Filed under: Non-technical — Jonathan Lewis @ 6:04 am GMT Jul 4,2013

I don’t know why I ever agree to go anywhere near Doug Burns – he usually manages to persuade me into doing things I don’t want to. This time (at a meeting of the London Oracle Beer group) he’s persuaded me that I really should join twitter. So I have (jloracle) – and found that I was being followed by four people before I even created an account, and was advised that I’d really, really, like to follow:

  • Jack Rivera
  • Justin Bieber
  • Jennifer Lopez
  • Katy Perry
  • Gwen Shapira

I had no idea who Jack Rivera might be, though I did recognise the next three names from those annoying ads that seem to appear on all sorts of news feeds. The one that baffled me was Gwen Shapira – by what mechanism did twitter manage to connect my name/tag/email address with someone relevant ?

Anyway, thanks, Doug – now I have to start thinking of something intelligent, perceptive or witty in 140 characters or less.


(I just got the Jennifer Lopez link –  JLOracle = J-Lo !)




May 13, 2013


Filed under: Non-technical — Jonathan Lewis @ 6:45 pm GMT May 13,2013

I’d like to dedicate this posting to fellow Oak Table member Richard Foote, for reasons that the readers we have in common will immediately recognise:

The singer is Canadian astronaut Commander Chris Hadfield who has been tweeting and posting pictures from space – be careful, you may get hooked:


When I posted the link to the video it had received 1.5M views; less than 24 hours later it’s up to roughly 7M. (And they weren’t all Richard Foote). Clearly the images have caught the imagination of a lot of people. If you have looked at the twitter stream it’s equally inspiring – and not just for the pictures.


October 29, 2012

Help Yourself

Filed under: Non-technical — Jonathan Lewis @ 5:17 pm GMT Oct 29,2012

When people ask for help on (for example) OTN, they are often asked to supply further information – sometimes in the form of requests for results from SQL queries. If you are ever in this position, you may find that you don’t understand what the query does, or why the information is useful – nevertheless you can still do something to make it as easy as possible for your potential saviour to help you.

Here’s an example to show you how NOT to do it:


August 29, 2012


Filed under: Non-technical — Jonathan Lewis @ 7:31 am GMT Aug 29,2012

Here’s the content of an email I sent to Packt back in February this year:

Please ensure that I don’t hear from Packt again.

I have been approached twice in the past and explained that I don’t have the time, and I’m not interested in reviewing books where I have had no involvement with the authors.

This elicited an apology, of course, then on 4th August (after two more pieces of spam from them) I sent them another email quoting the above with the following introduction:

November 18, 2011

Planet Earth

Filed under: Non-technical — Jonathan Lewis @ 1:52 pm GMT Nov 18,2011

I know it’s another post that’s not about Oracle, but someone sent me this video link a couple of days ago and it’s too wonderful not to share. (I’ve just got back from Iceland, so the Aurora Borealis at 1:05 is particularly relevant)

August 26, 2011

Big Numbers

Filed under: Non-technical — Jonathan Lewis @ 5:57 pm GMT Aug 26,2011

It’s hard, sometimes, to get an instinctive idea of how big a “big number” really is. I’ve just heard a brilliant description of a billion (American style: 109) that really gives you a gut feeling for how big the number is:

If you owed someone a billion dollars, and paid it back at the rate of $1 per second – how long would it take to pay off the debt (and don’t even think about the interest accruing) ?

The answer is 34 years.

The way I read it, that turns a big number into a number that’s small enough to comprehend but big enough to feel enormous.

April 29, 2011


Filed under: Non-technical,Oracle,Upgrades — Jonathan Lewis @ 6:06 pm GMT Apr 29,2011

Here’s a link to a truly ambitious document on Metalink (if you’re allowed to log on):

Doc ID 421191.1: Complete checklist for manual upgrades of Oracle databases from any version to any version on any platform

(Actually it only starts at v6 – but I don’t think there are many systems still running v5 and earlier).

April 24, 2011


Filed under: Non-technical — Jonathan Lewis @ 10:56 am GMT Apr 24,2011

How to ensure that you never give the wrong answer – as demonstrated by my bank’s telephone help system:

Stage 1 – after calling in through a special high-cost number, of course:

“{long message extolling the virtues of using the bank’s internet system for all your requirements}”

Stage 2 – you wait for the list of options to be recited

“Press 1 for …”
“Press 2 for …”

“Press 9 to speak to a member of the helpdesk”

Stage 3 – you decide the only relevant option is to press 9 to speak to a person:

“I’m sorry, I don’t understand what you want.” click, brrrrrrrrrrrrr …

Maxim: If you don’t want to fail, don’t even try.

November 12, 2010


Filed under: Non-technical — Jonathan Lewis @ 6:58 pm GMT Nov 12,2010

… (or “Fall” for speakers of American) has arrived in the UK – and once again I am reminded how gardening and trouble-shooting are just two aspects of the same problem.

I have several trees in and around my garden, including two rather large Oak trees, and at this time of year it takes a couple of hours at the weekend to rake up the fallen leaves. The comparison with solving performance problems is obvious:

Every Saturday, I look at the leaves on the ground and the leaves still on the trees and quite often manage to persuade myself that there’s no point in doing anything just yet.

On the Saturdays when I decide that I really do have to rake up the leaves I aim to clear about 99% of the problem – there’s no point in clearing to 100% because if I go for perfection it’s only going to last a couple of minutes before more leaves start coming down or blowing in. Of course, after I’ve spent ages clearing 99% of the mess, my wife (the end user) is quite likely to say: “you haven’t finished yet”

After I’ve done a really good job raking up enough leaves I look up at the trees and know that all those leaves are going to be heading my way and I’m probably going to have to do it all over again next week, and there’s nothing appropriate that I can do to stop it happening.


August 26, 2010


Filed under: Non-technical — Jonathan Lewis @ 9:41 pm GMT Aug 26,2010

Some readers have noticed that a few links to my blog seem to be broken. Don’t panic, it’s not permanent it’s just the result of Don Burleson losing his temper.

Let me start by telling you about DMCA, the “Digital Millenium Copyright Act”. DMCA is a mechanism designed to protect Internet service providers (ISPs) from being sued over content published by their customers by allowing them to act as a communication channel and staying out of the line of fire.

July 24, 2010


Filed under: Non-technical — Jonathan Lewis @ 7:11 pm GMT Jul 24,2010

I’ve been on holiday for the last few days – the last few posts were dated to publish themselves in my absence – and got home last night. First thing I did, of course, was to download my email … second thing the machine did was to declare an automatic software update and destroy the hard-disk on reboot. So I’ve downloaded but not read all the mail that was sent to me after 8:05 a.m. (BST) on Friday 16th July.

Luckily 8:05 am was when I took a backup of the system – as you do when you’re about to to on holiday – so I haven’t lost any data, except for those emails. So if you sent me anything important over the last week, please send it again.

Footnote: while I had a backup of all my data, I discovered (as one does until you practice recovery very regularly) that there were bits of information I hadn’t catered for: my address book and my mail rules, neither of which I had been exporting regularly, both of which are quite useful.

July 11, 2010

Don’t Knows

Filed under: Non-technical — Jonathan Lewis @ 6:29 pm GMT Jul 11,2010

One of the biggest problems in learning is that you don’t know how much you don’t know, and this raises two questions:

  • how do you find out that there are huge gaps in your knowledge that need to be filled ?
  • how do you know whether or not the material you’re learning from is any good ? (There’s a LOT of garbage on the internet.)

I can across an interesting little post from John Scott (of ApEx fame) a little while ago that shows the effect of the first question very clearly.

May 15, 2010


Filed under: Non-technical — Jonathan Lewis @ 10:24 am GMT May 15,2010

I’ve just received an email telling me that I’m a linchpin – according to this picture on Seth Godin’s website.

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