Re: DBA Interview Questions

  • From: ryan_gaffuri@xxxxxxxxxxx
  • To: dofreeman@xxxxxxxxxxx, "Oracle-L (E-mail)" <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 24 Nov 2004 20:07:47 +0000

is this a developer (coder) or a dba spot or a hybrid? also what is most 
important... someone very good at datawarehousing and ETL tools or someone 
intimately familiar with the database who can tune? If its the latter, you will 
have a better shot grabbing a production DBA and having the person write 
PL/SQL. Warehouse jobs typically pay well so it may not be as hard as it would 
be to grab a DBA and have the person do OLTP code. A good selling point for a 
prod DBA also is that data warehouse experience is far more valuable than OLTP 
experience in todays marketplace and its hard to break into the warehouse 

 its very hard to find a programmer who knows much about tuning. we had to 
reject 95% of our phone screens to get people who can do it here... and we are 
near DC with a large pool of applicants. Can't hire consultants so that does 
cut down on the top candidates somewhat. 

are you using RAC? if not, doesn't matter if they know it. 

Some questions that might help:
1. when do you use a bitmap index(since you have a warehouse). this is 
interesting because the oracle documentation is wrong. Most people recite the 
docs. Jonathan Lewis has some excellent articles about this on dbasupport(I 
think that is the write one...). 
2. in an explain plan what does cardinality and bytes mean and in what cases 
would either be useful? Cardinality is more useful when tuning oltp type 
queries and bytes is more useful when tuning bulk processing. 
3. the true senior question on the 10046 trace(curteous of cary milsaps book) 
what does it mean the your timing values = 0 in the 10046 trace? it means 
time_statistics= false and you need to turn it to true and retrace. 
4. for datawarehousing being able to interpret a query plan in advance of 
running the query is very important since queries can run for hours(even if 
they are optimized). I think the 10046 trace is less important than reading a 
query plan in your case. I would focus more on that. It's very hard to tune a 
query that takes hours based strictly off of a plan especially complex onces... 
5.  basic one, how do you speed up bulk processing? See if they atleat know to 
turn off constraints and triggers, etc... 
6. what does nologging mean? In a warehouse you will probably use that alot. 

if you find someone who has read dan tows sql tuning book and uses his 
strategy, you probably found a sql pro... 


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