What is a DBA?
A DBA is a Database Administrator, and this is the most common job that you find a database specialist doing. There are Development DBAs and Production DBAs.
A Development DBA usually works closely with a team of developers and gets more involved in design decisions, giving advice on performance and writing good SQL.
That can be satisfying at a human level because you are part of a team and you share the satisfaction of the team's accomplishments.
A Production DBA (on the other hand) is responsible for maintaining Databases within an organization, so it is a very difficult and demanding job. He or she, often gets involved when all the design decisions have been made, and has simply to keep things up and running.
Therefore, of course, it is also a rewarding job, both financially and in terms of job satisfaction. But it's a more 'lonely' job than being a Development DBA.
1. What DBA activities did you do today?
This is a loaded question and almost begs for you to answer it with "What DBA activities do you LIKE to do on a daily basis?." And that is how I would answer this question. Again, do not get caught up in the "typical" day-to-day operational issues of database administration. Sure, you can talk about the index you rebuilt, the monitoring of system and session waits that were occurring, or the space you added to a data file, these are all good and great and you should convey that you understand the day-to-day operational issues. What you should also throw into this answer are the meetings that you attend to provide direction in the database arena, the people that you meet and talk with daily to answer adhoc questions about database use, the modeling of business needs within the database, and the extra time you spend early in the morning or late at night to get the job done. Just because the question stipulates "today" do not take "today" to mean "today." Make sure you wrap up a few good days into "today" and talk about them. This question also begs you to ask the question of "What typical DBA activities are performed day to day within X Corporation?"
2. Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain, as the database is not cutting archive logs to disk.
3. Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
4. Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
5. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.
6. What command would you use to create a backup control file?
Alter database backup control file to trace.
7. Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened
8. Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.
9. Explain the difference between $ORACLE_HOME and $ORACLE_BASE.
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
10. How would you determine the time zone under which a database was operating?
select DBTIMEZONE from dual;
11. Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.
A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.
12. When a user process fails, what background process cleans up after it?
PMON
13. Describe what redo logs are.
Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.
14. How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;
15. What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace?
A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.
A DBA is a Database Administrator, and this is the most common job that you find a database specialist doing. There are Development DBAs and Production DBAs.
A Development DBA usually works closely with a team of developers and gets more involved in design decisions, giving advice on performance and writing good SQL.
That can be satisfying at a human level because you are part of a team and you share the satisfaction of the team's accomplishments.
A Production DBA (on the other hand) is responsible for maintaining Databases within an organization, so it is a very difficult and demanding job. He or she, often gets involved when all the design decisions have been made, and has simply to keep things up and running.
Therefore, of course, it is also a rewarding job, both financially and in terms of job satisfaction. But it's a more 'lonely' job than being a Development DBA.
1. What DBA activities did you do today?
This is a loaded question and almost begs for you to answer it with "What DBA activities do you LIKE to do on a daily basis?." And that is how I would answer this question. Again, do not get caught up in the "typical" day-to-day operational issues of database administration. Sure, you can talk about the index you rebuilt, the monitoring of system and session waits that were occurring, or the space you added to a data file, these are all good and great and you should convey that you understand the day-to-day operational issues. What you should also throw into this answer are the meetings that you attend to provide direction in the database arena, the people that you meet and talk with daily to answer adhoc questions about database use, the modeling of business needs within the database, and the extra time you spend early in the morning or late at night to get the job done. Just because the question stipulates "today" do not take "today" to mean "today." Make sure you wrap up a few good days into "today" and talk about them. This question also begs you to ask the question of "What typical DBA activities are performed day to day within X Corporation?"
2. Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain, as the database is not cutting archive logs to disk.
3. Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
4. Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
5. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.
6. What command would you use to create a backup control file?
Alter database backup control file to trace.
7. Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened
8. Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.
9. Explain the difference between $ORACLE_HOME and $ORACLE_BASE.
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
10. How would you determine the time zone under which a database was operating?
select DBTIMEZONE from dual;
11. Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.
A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.
12. When a user process fails, what background process cleans up after it?
PMON
13. Describe what redo logs are.
Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.
14. How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;
15. What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace?
A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.
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