oracle工程师面试题－e文转贴

oracle工程师面试题－e文转贴

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oracle工程师面试题－e文转贴

2006年4月20日 21:17:01

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 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.
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 two examples of referential integrity
constraints.

A primary key and a foreign key.

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 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.

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.