Skip to main content

Program doing the impossible? Check your assumptions!

Have you ever had one of those days when you run your program and it does the impossible?

As in, you stare at the screen and say: "No way, that's impossible. My program couldn't have done that. Couldn't be doing that."

It's a funny thing for a programmer to say, when you think about it.

We are logical people - or at least we are expected to use logic in our jobs.

And that is flat out a most illogical statement - contradictory on the face of it.

Because it wasn't impossible. Obviously. It just happened.

So what's a programmer to do?

Check your assumptions!

You must have made an assumption that is not valid. Assumed that data was in the table that was not - or vice versa. Assumed that you saved a change to your program that you did not. Assumed that you recompiled your program, when you had not. Etc., etc.

Here's an embarrassing true story from my own long, sordid history of programs doing the impossible due to my stubborn refusal to go back and revisit my assumptions.

Hopefully you've heard of the PL/SQL Challenge, a website offering weekly quizzes on SQL, PL/SQL, Database Design and Logic.

I built the website with lots of help from John Scott, Dimitri Gielis and Paul Broughton (all with APEX Evangelists back then). We planned to launch the site on 1 April 2010. And I promoted the site heavily. There was lots of excitement in the Oracle developer community.

New project by Steven! Let's check it out!

We started the site with a daily PL/SQL quiz (that's right - a daily quiz, which went on for four years. Lots of quizzes!), and each day started one second after midnight UTC time (formerly known as Greenwich Mean Time). So John and Dimitri and Finn (my co-founder of the PL/SQL Challenge) were waiting at their machines at midnight. It was 6 PM in Chicago. The second hand swept past 12 and the PL/SQL Challenge was born!

Hundreds of eager developers clicked the Start button to take the quiz - and the entire website froze. Like glacial ice. Sweat broke out on my forehead. I was frantic. Skype messages and calls flew furiously back and forth across the Atlantic.

What the heck was going on? We checked this, we checked that. We agonized. For hours.

And how could it be that with all these Oracle experts on hand, especially the amazing Steven Feuerstein, that we couldn't sort out the problem?

Well, the main problem, it turned out, is that John and Dimitri and Finn all trusted me to not be an idiot.

And at 4 AM, I was able to confirm that I was an idiot. Because I had issued a command to insert a row into a table, a row that was necessary for the site to work properly.

But I had not issued a commit.

I executed "COMMIT;" and the website unfroze. Bottlenecks disappeared. Quizzes could be played. And life did go on. The PL/SQL Challenge went on to attract thousands of developers, with between 500 and 1200 people playing each day for four years.

[We've since "settled down" to an array of 10+ weekly quizzes.]

And looking back on it, it's hard to believe that we couldn't diagnose the problem more quickly. Hard to believe that I could sit there insisting that I'd done everything I needed to do. And that there was no possibility of a data error.

Hard to believe that it happened, except that it did.

And it was a great reminder that when we are under lots of pressure, we don't always think as clearly as we could and should.

So what's a developer to do?

Make a checklist of all the assumptions you have made, and then go over those assumptions: True? Valid?

And once you've gone through that list, without getting to a resolution, ask yourself: what other assumptions am I making that I don't even realize I am making?

Hey, who ever said that programming was easy?
Labels:

Comments

Post a Comment

Popular posts from this blog

Why DBMS_OUTPUT.PUT_LINE should not be in your application code

A database developer recently came across my  Bulletproof PL/SQL  presentation, which includes this slide. That first item in the list caught his attention: Never put calls to DBMS_OUTPUT.PUT_LINE in your application code. So he sent me an email asking why I would say that. Well, I suppose that is the problem with publishing slide decks. All the explanatory verbiage is missing. I suppose maybe I should do a video. :-) But in the meantime, allow me to explain. First, what does DBMS_OUTPUT.PUT_LINE do? It writes text out to a buffer, and when your current PL/SQL block terminates, the buffer is displayed on your screen. [Note: there can be more to it than that. For example, you could in your own code call DBMS_OUTPUT.GET_LINE(S) to get the contents of the buffer and do something with it, but I will keep things simple right now.] Second, if I am telling you not to use this built-in, how could text from your program be displayed on your screen? Not without a lot o...
4 comments
Read more

The future of Oracle PL/SQL: some thoughts on Sten Vesterli's thoughts

Sten Vesterli published a very thought-provoking post on his blog: Please stop reading this post, and read that one. When you are done, come on back here for my thoughts on Sten's thoughts. OK. You read it. Here we go. First, thanks, Sten, for being such an interesting, wise, sometimes provocative voice in our community. Next, Sten writes: Now, on the one hand, I certainly agree that the vast majority of young developers are currently caught up in the modern version of a Gold Rush, which is: "Build an app using JavaScript, pay no attention to that database behind the curtain." But I can assure you that I still do meet young PL/SQL programmers, regularly, when I am at conferences and doing onsite presentations at companies. So, young person who writes PL/SQL: do not be afraid! You are not alone! And you are super-smart to have made the choice you did. :-) Next, Sten offers this advice to managers: I agree that PL/SQL is a "spec...
46 comments
Read more

Table Functions, Part 1: Introduction and Exploration

Please do feel encouraged to read this and my other posts on table functions, but you will learn much more about table functions by taking my Get Started with PL/SQL Table Functions class at the Oracle Dev Gym. Videos, tutorials and quizzes - then print a certificate when you are done! Table functions - functions that can be called in the FROM clause of a query from inside the TABLE operator - are fascinating and incredibly helpful constructs. So I've decided to write a series of blog posts on them: how to build them, how to use them, issues you might run into. Of course, I am not the first to do so. I encourage to check out the  documentation , as well as excellent posts from Adrian Billington (search for "table functions") and Tim Hall . Adrian and Tim mostly focus on pipelined table functions, a specialized variant of table functions designed to improve performance and reduce PGA consumption. I will take a look at pipelined table functions in the latter part...
31 comments
Read more