Interviewing Oracle DBAs

You may have seen in an earlier article I was trying to drum up interest in a recruitment drive we were having. Well, we whittled down the applicants and recently held the interviews. There was one candidate that stood out quite away above the other hopefuls. I thought it might be of interest to go through some of the interview questions that we used. I know Howard J. Rogers (currently and perhaps permanently off air) has in the past written a fantastic series of pieces on his interview questions, but I feel our experience is worth sharing. Though it seems the lack of good quality Oracle DBAs is a universal theme.

First off, I think it is fair to say the interview was split roughly in two, with the first half covering more attitudinal questions and the second half covering more technical Oracle questions. We certainly place as much weight on finding the correct sort of candidate, one with a good attitude to learning and customer service, as much as what particular level of Oracle skills they have. Also it’s worth pointing out this is for a job in a small company, where there is no strong demarcation of responsibilities, so the DBAs are expected to do a goodly amount of system administration work, and have ownership of configuring the SANs. The candidate we chose I would say displayed excellent answers in both the attitudinal and technical questions. Here are the Oracle questions we asked, I think these are pretty straightforward and gentle questions, there are not even that many of them!

What approach would you take if asked to investigate a query that was running slowly?

A couple of candidates answered this pretty well. I was looking for things like checking the explain plan, and tracing the session. I was not looking for someone to mention the buffer cache hit ratio – though someone did!

What SQL commands will cause a sort to take place?

Unfortunately a few candidates did not get past order by (which all got), some said distinct and group by. The candidate we hired mentioned these and UNION. No one mentioned create index.

How does Oracle implement read-consistency?

Quite a few candidates stumbled at this question. It is such a fundamental part of the Oracle RDBMS that you would hope a candidate would at least have go at answering. A couple of candidates said they were stumped. I was looking for them to mention that a query only sees data committed before the start of the query and uses undo to reconstruct any data if it finds it with a commited time that was after the start of the query. No one mentioned SCN.

Do you know what ORA-01555 is?

This is somewhat related to the previous question. Practically every candidate did not know this. I do not expect a candidate to know every single Oracle error message, I certainly don’t. However 1555 is such a classic error that I would expect good dbas to know what it is. The one candidate who did know that it’s snapshot too old, got the job.

What resources do you use to keep up-to-date with Oracle?

Well I probably was a little disappointed with the responses to this one, only one candidate mentioned a good spread of bloggers, or indeed blogs at all. Everyone mentioned OTN, but no one mentioned actually downloading a new release and trying it out for themselves. Oh and this question lead on to which authors the candidates liked, Tom Kyte was the definite winner with Steven Feuerstein in second place. I was astounded not one candidate mentioned Jonathan Lewis.

Explain the architecture of RAC?

So, I realise this could potentially lead to a wide ranging answer, but most of the candidates had RAC on their CV so you’d expect them to able to explain it at least to a level that they new it was different from single instance Oracle. Minimum requirement was multiple instances accessing the same database datafiles, communicating through a private interconnect, which most met.

Finally, here is one of the non-technical questions we asked:

What kind of working environment do you need to be most effective?

I’ll leave it to the reader to work out what we expected from this one!

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7 thoughts on “Interviewing Oracle DBAs

  1. Hands down a really awesome oracle DBA is hard to find. I live in LA and it seems that every business colleague of mine is looking for a good one. My company just started to look in middle earth as well as the east coast due to lack of availability. It’s important to find someone who is willing to learn as well as having an overall passion for Oracle….. Good luck colleague and great post/questions!

  2. I hope you’re going to change the questions next time around Jason, or else we’ll just get some hobbit who happens to read your blog getting the job! (Does middle earth = mid west, europe or what?)

  3. Howdy Chris,

    I’m not sure my blog reaches middle earth, but if the candidate has a good positive attitude to learning, does not mind a relaxed environment, and knows one end of a shutdown command from a startup command, they’ll probably do alright, whether they are a hobbit, dwarf or elf.

    Not many of the candidates actually mentioned blogs, and anyway most of my readers already work for Nominet!

    jason.

  4. I don’t know what I think of the interview questions I see on various blogs. I’m convinced that some of them are just so the interviewer can feel clever.

    How about this as a technique. Say you have a requirement that a DBA knows dataguard. Allocate one section of the interview to this topic. Start a conversation about dataguard using very open questions ie not a specific question about what does this ORA error mean. Get the person talking about dataguard, what s/he knows, doesn’t know, experience. Then start drilling down with some specifics. Asking very specific questions in the beginning may not tell you everything you need to know about them.

    So I don’t think you need to ask a DBA what SQL causes a sort. If you know the topic, then a conversation with the candidate will tell you much more than pointed questions.

  5. Hello Chris S,

    Thanks for reading! I think I pretty much agree with what you say. The first half of the interviews we did were far more conversational, trying to get a feel for how the person thought and what attitude they would have. The weight placed on this in choosing the candidate was quite high at least 50% probably higher.

    The Oracle questions, I thought were mostly of a general variety, we did not really have a particular oracle skill set requirement, we would have been happy to train the right candidate in RAC or dataguard or whatever oracle technology was required.

    Trust me, it was pretty irrelevant if the candidate knew the ORA-01555 question, – lets call that one the tie breaker, not that we actually needed it.

    cheers,

    jason.

  6. 2. What should you do when you find a stacktrace in the server errorlog ?
    3. What do you do when the server can’t start due to a corrupt master database ?
    4. How do you BCP only a certain set of rows out of a large table ?
    5. What would you do when the ASE server’s performance is bad ?
    6. What do you do, when tempdb is full ?
    7. About Replication server setup & sync ?
    8- How you handle problem ticket?

    9 how to estimate the size of SGA????
    10 What is your typical day like?
    11 Do you consider yourself a development DBA or a production DBA and why?
    12 Different audit Oracle & Sybase
    13 setup sybase replication? Oracle dataguard

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