Monday, January 26, 2009

The courage to say the impossible

I was interviewing a guy the other day for a DBA position I have open and I like to ask questions that help me determine how much someone's actually worked with SQL. And one of the ways I'll do that is to ask them how to perform an impossible task and see how they deal with it. In this case, I asked how he would restore a single table from a backup.

He thought about it and went through different scenarios, all of which I kept narrowing down until he was forced to deal just with the backup file itself with no other parameters. He kept trying to think of the flag that he would use to just pull a single table out of that file and he just couldn't think of it. He finally said that he didn't know of a way to do it, but he was willing to learn.

He failed that question in a couple of ways. First and foremost, he had to thing too long and hard about something he should've known for as long as he's been a DBA. So there's that. 2nd, he failed because he didn't have the courage to tell me that it wasn't possible and that as a user, I'm screwed. The data can't be recovered that way. Now, this is a very valid question and tells me a lot about a DBA because we're quite often called on to deliver bad news and if you're not able to do that, then you may not be as strong as you thought.

What he needs is the courage to stand up and tell me that what I'm asking for isn't possible, but he was too caught up in the fact that he's in an interivew and I wouldn't be asking a question like that if I didn't know of a way to do it. I actually explained all this to him and he agreed and said that he thought it was a trick question, but didn't want to say anything.

I've been in that position before where I was thrown by a T-SQL question like that. And initially I reacted the same way because there are so many pitfalls and neat little tricks in the sql lang that I could easily have missed something really big. Or there could have been some obscure legacy trick that still worked. So I get where he's coming from. I really do. However, backup syntax isn't like that at all. It all fits on one page so it's a lot easier to lookup.

And not to go off on too big of a tangent, sales guys are the same way. They hate to say no to a client. They feel it's the worst thing they could do, but it's not. The worst thing they can do is to make promises they can't keep. I saw this at a gig I had about 4yrs ago a lot. The sales guys were always making promises and then expecting the devs to deliver on time. It's messy, and it promotes nothing but crap code. So while they always made their deadline the software was so buggy and so poor with concurrency, it spent more time down than anything. So while they met the letter of the contract, they've greatly harmed their reputation and pissed off the client because now they've gotta take a couple more weeks to fix issues. And that could really harm the client's data as well. Because you could have to make changes to the underlying schema and now you're in the middle of a conversion right after you go live. So I realize you don't want to have to tell a customer no, it's best to tell him the truth. As much as I'd like to get this entire app architected and fully written by this time next month, that's just not realistic. Why don't I get back to you on when we could have a complete product ready, or we can work out a release schedule and we can get you the most critical functions right away and then bring others online as they become available?

So while nobody wants to say no, or that's not possible, or your data's gone for good, it's necessary sometimes and your customers (whoever they are) will appreciate your honesty. And they'll appreciate that what you give them will actually work when it's released.

And by all means, if you're interviewing and you're put in an impossible situation, don't be afraid to say it's an impossible situation. Acknowledge to the interviewer that you realize your choices are limited and that your actions will be factored by that limitation. Then present them with the possible solutions and leave it at that. In this exact case I gave above, the answer would have been something like this:

Well, you can't restore a single table from a native sql backup. If you had some kind of 3rd party product like LiteSpeed or Red-Gate or Hyperbac I could do something for you. But as it stands, you have to restore the entire DB. If you were lucky enough to at least have filegroup backups We might even be able to get away with a partial restore if the table's in the right filegroup. But the situation as you've outlined is pretty bleak.

That answer tells me a couple things. It tells me that you know right away that the task is impossible. So you've worked with sql backup before. It also tells me that you know the situations where what I'm asking would become possible and you've done it enough to know those other solutions immediately. And it shows me that you're willing to be honest with me about my situation. That kind of answer will win a lot of points because if I actually had this problem, you would be the one I wanted to clean up my backups going forward because you've clearly been there before and are quite capable of putting me in a better position. And as an interviewer I may or may not realize that's what's going on, but I'm digging you pretty well right now.

And don't be afraid to tease a little. I had an interview once where they were having problems with SQL memory. They wanted to access more than 4GB, and had the RAM installed, but couldn't get SQL Server to recognize it. I gave him some guidance on how he would see that memory used in SQL and he said that it was perfect for his scenario. Then he asked what they did wrong and how to fix it. I said, well sounds like you need a DBA and if you bring me aboard I'll be happy to help you with that.

So there ya go. There's a little how and why on answering interview questions. There are ways to answer questions that tell them you have experience and ways to answer that don't tell them much about you at all.

Good luck.

4 comments:

Anonymous said...

Gee, that's not impossible. But you do have to go around your fingers to get to your thumb!

Why wouldn't you simply restore the backup into a differently named database (e.g.: restore database [foo] into [foo_restore] ...) and then retrieve the table schema and or data from the restored database?

Granted, it's not a single command, and you do have to restore the full database backup, but it's a workable solution to retrieve a table. If you have the space available. :)

Sean McCown said...

Well, restoring the DB under a different name wasn't part of the scenario. In the question, the DB was actually too big to house a 2nd time so you had no choice but to try to pull the table out by itself. And that was the point. I've got these guys telling me they're experts in backup/restore so they should know it's not possible. It was a simple exercise to see if they'd ever actually worked with the product.

Anonymous said...

many times, I felt that IF I ask a question back to some of the stupid GREAT INTERVIEWER guys, you will keep your mouth shut. (I know some won't because they like to blah blah blah and ) Simply teasing someone when you know what you don't know is crap.

Okay. I am mad with a Senior Architect who proved to be a knucklehead and was farting. Who knows that idiot is having a blog publishing I had an interview today with Mr.X and you know a lot of lies to show off that he is simply great.

I am mad and this gives me some releif. Holy crap. Nothing against you.

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