1. 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 ball
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.
2. You have just had to restore from backup and
do not have any control files. How would you go about bringing up this
database?
I would create a text
based backup control file, stipulating where on disk all the data files where
and then issue the recover command with the using backup control file clause.
3. How do you switch from an init.ora file to a
spfile?
Issue the create spfile from pfile
command.
4. 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.
5. Give two examples of how you might determine
the structure of the table DEPT?
Use the describe command or use the dbms_metadata.get_ddl package.
6. Where would you look for errors from the
database engine?
In the alert log.
7. 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.
8. Give the reasoning behind using an index?
Faster access to data blocks in a table.
9. Give the two types of tables involved in
producing a star schema and the type of data they hold?
Fact tables and
dimension tables. A fact table contains measurements while dimension tables
will contain data that will help describe the fact tables.
10. What type of index should you use on a fact
table?
A Bitmap index.
11. Give some examples of the types of database
contraints you may find in Oracle and indicate their purpose?
A Primary or Unique Key
can be used to enforce uniqueness on one or more columns.
A Referential Integrity
Contraint can be used to enforce a Foreign Key relationship between two tables.
A Not Null constraint -
to ensure a value is entered in a column
A Value Constraint - to
check a column value against a specific set of values.
12. 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.
13. 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 ball in time.
NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the
disadvantage of not being able to recover to any ball 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.
14. What command would you use to create a backup
control file?
Alter database backup control file to trace.
15. 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
16. What column differentiates the V$ views to
the GV$ views and how?
The INST_ID column which
indicates the instance in a RAC environment the information came from.
17. How would you go about generating an EXPLAIN
plan?
Create a plan table with
utlxplan.sql.
Use the explain plan set
statement_id = 'tst1' into plan_table for a SQL statement
Look at the explain plan
with utlxplp.sql or utlxpls.sql
18. 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.
19. 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.
20. 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.
No comments:
Post a Comment