Monday, March 31, 2008

The Untunable Database

There are some DBs that just can't be tuned any more than they already are (or aren't). A good example of this is an application that hits a DB and never qualifies any of its queries. They all hit with select * and no where clause. There's really nothing you can do to increase the performance short of just throwing more spindles at it. But that's not really what I'm thinking about right now. What I've got on my mind now is an application and DB that just can't be tuned no matter what you do because the business owners don't see the benefit of making the changes.

I saw that a lot when I first got to my current gig. We had queries doing horrendous things and taking several hours to return and nobody cared. The end users had been running these queries for years and were happy with them. They didn't care that the server was maxed out all the time and that they had to wait 12hrs for a report to return. Now, I don't have to tell you that as a DBA that just drives me insane. Not to mention that it gives me nothing to do. Why am I even here then?

So with that in mind, I had to go a little cowboy on them and just start making minor changes that proved my point. I really can't stress enough that I'm against going cowboy on any DB and I don't care who you are. But there are some instances where it's warranted. You have to get the ball rolling somehow. And how this DB got in such bad shape was definitely their fault, but their current view wasn't. They had just been so used to things working the way they were that they didn't see the need to change. They got their reports more or less when they expected them and even if they had to wait a couple extra hours for them they didn't really mind because they understood the server was busy.

So what I did was just start by indexing a couple huge #tables. I just picked a couple of the worst SPs and added a couple indexes. Then I went in and started commenting out cursors and replacing them with simple join queries. Both of these made a huge difference. Then I just sat back and waited. You really don't want to go too far with something like this. Then when they started noticing that their 12hr queries were coming back in just a few secs, then I had their attention. I was then able to convince them to let me go even further and start really tearing into some of these SPs.

And now, for the first time ever, we've got a near-realtime reporting effort in our company. They've come a long way from 'I don't care if it takes 12hrs' to 'I have to have it now'. The problem is they still slip back into their old habits now and then. They currently want to implement an encryption solution that will take around 2mins to return for each report when the solution I suggested returns in about 2secs. And sure, 2mins isn't really going to break the bank, but as those of you who have done a lot of query tuning should know, you have to be hungry for resources. You have to treat every single CPU tick as a drop of water in the desert. If you don't, you'll wake up one day and be in the middle of the same shit you were in before. You have to fight over milliseconds and squeeze every last drop of performance out of every query you can find. That's the only way to run a real tuning effort.

But it's amazing how politics and perception find their way into every aspect of your job.


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Sean McCown
I am a Contributing Editor for InfoWorld Magazine, and a frequent contributor to as well as I live with my wife and 3 kids, and have practiced and taught Kenpo for 22yrs now.
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