What's a 'Data Warehouse DBA'?

I've seen that question asked often in forums and mail groups. It's easy to understand why there's so much confusion because, for most DBAs, if you've seen one database, you've seen them all. Or rather, you haven't seen any of them. What I mean is that every database that lands in your hands is new, has it's own users, it's own problems, it's own performance profile. So learning and coping with new situations is an implicit part of being a DBA and if you're a *good* DBA, a data warehouse should be well within your capabilities.

The very first Oracle database I worked on was a data warehouse, although possibly not in the sense we understand today. It didn't use a Kimball-style data model, materialised views didn't exist in Oracle and the volumes of data were tiny compared to current warehouses. However, it did have a fact table for all of our customers, one for all of their accounts, a many-to-many join table between the two and tons of small? reference tables. We used it to run complex, user-defined queries to generate lists of customers for direct marketing mail-shots.

When recruitment agents started to ask me about my Data Warehouse experience, I was very blas� in response because I know my skills are up to most jobs and was frustrated when they wanted to see 'Data Warehouse DBA' on my cv. To my mind a good DBA is more than capable of looking after Data Warehouses too and it doesn't help when slightly famous bloggers say things like (and this isn't a direct quote) 'I do data warehouses - they're different'. Which is weird, because you don't see people going around saying 'I do several thousand user OLTP systems'. My point here is that there is a certain cliqueness or possibly? elitism? about the DW crowd. Now, before I upset everyone (because all of my friends seem to be members of that crowd ;-), let me explain why I think they're like that.

I work with the DW development team quite a lot in my current workplace. One of the reasons for that (and I'm going to have to leave my modesty to one side for a moment) is that they could quickly spot that I knew what I was doing. That's the good thing about the DW crowd - they're quite demanding. Whilst working with them, I heard horror stories about what previous DBAs had done, so they are very twitchy about the skills of the people who work on their databases. In fact, we had a DBA start here not so long ago and the first bit of advice I gave him was 'when the DW guys ask you to do something, the chances are that they understand the reasons for it better than you do.' But that's because they spend all of their day working on the same couple of databases. They have tons of time to think through the issues. It's not because they're party to some mysterious knowledge that takes years to learn (or at least no more mysterious than just being a DBA on big databases).

To further counter my own argument, here are some things that I think are definite requirements for a DBA to work on Data Warehouses (even if they choose not to glorify themselves with the full title)

1) Knowledge of Partitioning, Materialised Views, Bitmap Indexes, Parallel Execution and, in fact, most things in the handily-supplied Data Warehousing Guide

2) Knowledge of the latest features because DW systems always seem to be on the latest release because they need the features.

3) Experience of working with big databases. This sounds obvious, but how do you go about backing up a 2Tb warehouse? Maybe it makes more sense to rebuild indexes than backup the tablespaces. Believe it or not, there *might* be good reason for having a tablespace with hundreds of files - just because you haven't seen one before doesn't make them bad

So I'm not saying working with Data Warehouses is easy, just that it's not some black magic art-form. I repeat - the most important thing is that you're a good DBA in the first place and that you're open-minded.

Actually maybe I've argued my way into a corner here and there is a lot to being a Data Warehouse DBA but it just doesn't seem that big a deal to me. Maybe I've got more experience than I think I have and I should start calling myself a Data Warehouse DBA, however .... The other week I had a conversation with a recruitment agent that spread over several phone calls and ultimately degenerated into a series of 'so how big was that database, then' questions, going through each of the sites I'd worked at. His client's requirement was for DBAs who'd worked on Terabyte warehouses and, as some of mine were only six or seven hundred gig, it was proving tricky. Eventually I gave it up as a lost cause but it is disappointing that this job title might be excluding good DBAs from jobs because they don't see it as being a specialised position and therefore don't see the need to change the job title on their cvs (or blog!).

To be honest, I'm feeling pretty depressed about the state of the DBA role this month, so expect this to be one of a series of rants.