DataBase Administrator (DBA) Interview Questions and Answers
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16. What is a Segment?A segment is a set of extents allocated for a certain logical structure.
17. A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables?
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.
18. 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.
19. What is a Sequence?
A sequence generates a serial list of unique numbers for numerical columns of a database’s tables.
20. Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT - Instance startup
21. What is a Synonym?
A synonym is an alias for a table, view, sequence or program unit.
22. How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
23. How would you go about increasing the buffer cache hit ratio?
Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.
24. 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.
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