Senior Database Administrator (DBA) Interview Questions

Senior Database Administrator (DBA) Interview Questions and Answers

This set of interview questions for Senior Database Administrators (DBA) help you evaluate candidates' skills and qualifications to make more informed hiring decisions.

Interview questions for Senior Database Administrators (DBA)

Interview questions for Senior Database Administrators (DBA)

A table without a clustered index is called...?
Answer: HEAP

How many bytes an index key can have at the maximum in SQL Server 2016? 
Answer: 900

Can you tell what types of APPLY operators exist in SQL Server 2016?
Answer: OUTER APPLY, CROSS APPLY

What type of an index can have less rows than it's table?
Answer: FILTERED index

Name two reasons why would UNIQUEIDENTIFIER data type (aka GUID) be a bad choice for a clustered key?
Answer: Because of FRAGMENTATION it causes and large SIZE (16 bytes)

The choice of a clustering key columns of a clustered index is crucial for performance. Name at least three characteristics that a good clustering key should have.
Answer: UNIQUE, SLIM SIZE (small width in bytes), EVER INCREASING, fixed width, not null

Wi have a single UPDATE command that changes 100 rows of a table. Table has trigger that fires after update. How many rows do we have in INSERTED, UPDATED and DELETED metatables that we can access within a trigger code?
Answer: INSERTED: 100 rows, DELETED: 100 rows, UPDATED: that is made up (does not exist)


If not executing on the CPU, sessions wait for various things. What should we use to programmatically check what the sessions are waiting for, in cumulative total of all the sessions from the start of the server?
Answer: DMV called sys.dm_wait_stats. The answer „a DMV exists but I cannot recall it's name“ is not bad also.

In which recovery models the minimally logged operation is possible to occur?
Answer: SIMPLE and BULK_LOGGED.   (If he mentiones FULL in addition to those two, it is a wrong answer)

We have a database in full recovery model, and transaction log file size of 100 GB. We have a long running transaction, running for many hours. If the last log backup was taken just now, how big the log backup file will be if we take another log backup immediately after this one? 
Answer: 0MB (or close to zero)


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