Montag, 20. Juni 2011

ORA-02393 on purpose

Today I got an email by a developer about an error on a test database.
(I shortened the conversation, but tried not to change the content):


Dev:
We get an ORA-02393: exceeded call limit on CPU usage almost immediatedly after executing the following stmt: ...Could you pls adjust the limits?



After some hours of meetings I replied:
Me:

These limits where introduced in test to find exactly those statements which are running too slow for an OLTP application. Can we help you in tuning the statement?

Dev:
I already exchanged details on the issue with [another DBA] and found the cause of the 'longer than usual' execution time (index missing ;-)
Nonetheless 100ms max exec time is a bit too strict for a dev platform imho - but as the ... is going to be replaced soon we won't request any changes to a system/db in the last chapter of its life cycle.


I did not reply yet. Just try to explain my world.

Is a CPU_PER_CALL limit really needed on a test system?


In theory: no.

If the developers implement a perfect code instrumentation, they would know the runtime of every statement. In test it would be evaluated for a proper per-statement performance as well as for an over all performance.

But if they would do so, I would never have received this email. So the world is not perfect. The code isn't, also.

Are 100ms enough time? seems really tough!


Yes, they are.

Even on an 8 years old UltraSparc III+ you can do a lot of CPU cycles within 100ms. And only CPU is count there, no time for IO or other WAITs.

But the biggest argument for this limit: I never got any complaint about it by a good statement. Only by those which needed urgent suport, anyhow.

Montag, 6. Juni 2011

Access to the database

There is a kind of discussion ongoing who should have access to a database, and under what circumstances.
I have never done either of Jeffs or Chets job, so I cannot write anything reasonable about these. But I am sometimes a kind of DBA. This makes me my best source of knowledge about this job, and the attitude I created during the years.

I developed a certain expectation about the differences between an operation guy and others, who are not responsible for productive systems. I even have my private opinion about a sales related job, but that's not my topic today.

From my point of view it's all about control.
For an operational focused person, my work is about control. If there is uncontrolled behaviour somewhere, this will lead to an incident. And that will causes a call. As I like to sleep at least 8 hours per day, that means one out of 3 calls will disturb this sleep (on average).
Of course every incident potentially costs my company money. Or reputation. This will come down to me again. Writing reports. Doing management presentations. Nonproductive paperwork.
After all this additional work, I will do my best to avoid this situation. Analyzing what went out of bounds, led to this uncontrolled behaviour. At the end I even try to change the environment so this will not happen again.
It's all about control. Freak!

So who should get access to my systems? Only those whose I can control. Or at least I can trust?

It's hard to decide whom to trust. At least to which specific level.
Jeffs driving license seems to be a try to formalise this need. But similar to a driving license, it only shows you have the allowance to drive. It rarely tells anything about the skills.

Talking about skills brings one more dimension here: People living in an ecosystem where every action is controlled by a QualityAssurance team are used to go to the limits and beyond. That's great, it's what is expected from them. Otherwise they would do their job bad.
It's just not what I want in a productive environment. There boundaries are, to never be reached.

I put a more pragmatic approach: If someone takes responsibility for the work, it's fine for me. As an example: if the person who added a big bug during a small hotfix at 5pm is called at 2am the next morning to fix this bug, I'm fine.
And just one more dimension: I favour to grant access to people who know what they can break with this: Just ask me for any access to v$ views in my DB; you will get it, just after you show and explain me how you can halt the application if you abuse it.

Need a short summary?
I like to control access to my database, so I limit it to people who I trust.
To gain it, show me your responsibility and knowledge.

Mittwoch, 1. Juni 2011

Artist of Farmer?

This morning I read a twitter message by Jeff Smith (aka @hillibillitoad):
OH: "Once we get our system running, we don't touch it." Yeah, that generally works pretty good.
I like Jeffs tweets, blogs and comments as he is a very smart guy and still keeps his mind open for other ideas.
In this particular case I have to contradict, but I was not able to condense it into 140 chars.



Most people in the IT business seems to follow the sentence "never touch a running system" like a commandment. For me this often sounds like the "please don't touch" in an art museum.



This brings me to an interesting question: Do these 'most people' see themselves as artists, and their work as art?


Let me give you another picture:


Imagine a farmer which seeds the crops in spring, did really everything right and then sits down and does not touch his running system. You might guess his harvest?



So what's the big difference here?
Artwork most of the time is first created for a dedicated purpose. As long as the purpose does not change, it's expected to satisfy this purpose.
The purpose of an artwork slowly changes, I'm quite sure most of the time it can be measured in decades or centuries.
Also plants are seeded for a dedicated purpose. But their purpose is the rapid change. To live, to growth, to get harvested after some time. So the farmer has to look after his crops all the time. In the best case, he even can improve and steer the change to his advance.
For me the big difference between an artist ('don't touch') and a farmer ('care and steer') is the timescale of the changes. If you expect your work to be never changed (and in a definition of 'life' things which do not change are just dead) prevent them from any interaction.
I prefer living systems. So I take the duty and care for them.