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ORACLE Tutorials

FAQs on Oracle, SQL and PL/SQL including DBA Questions and Answers:

FAQs on Oracle, SQL and PL/SQL including DBA Questions and Answers:

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.
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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.
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3. How do you switch from
an init.ora file to a spfile?
Issue the create spfile from pfile
command.
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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.
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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.
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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.
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8. Give the reasoning
behind using an index. Faster access to data blocks in a table.
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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.
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10. What type of index should you use on a
fact table? A Bitmap index.
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11. Give two examples of referential
integrity constraints. A primary key and a foreign key.
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12. A table is cla*sified 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.
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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.
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14. What command would you use to create a
backup control file? Alter database backup control file to trace.
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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.
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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
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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.
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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.
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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. 1. Describe the difference between a procedure,
function and anonymous pl/sql block. Candidate should mention use
of DECLARE statement, a function must return a value while a procedure
doesn?t have to.
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2. What is a mutating
table error and how can you get around it? This happens with
triggers. It occurs because the trigger is trying to update a row it is
currently using. The usual fix involves either use of views or temporary
tables so the database is selecting from one while updating the other.
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3. Describe the use of
%ROWTYPE and %TYPE in PL/SQL Expected answer: %ROWTYPE allows you
to a*sociate a variable with an entire table row. The %TYPE a*sociates a
variable with a single column type.
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4. 4What packages (if
any) has Oracle provided for use by developers? Expected answer:
Oracle provides the DBMS_ series of packages. There are many which
developers should be aware of such as DBMS_SQL, DBMS_PIPE,
DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB,
DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and
describe how they used them, even better. If they include the SQL routines
provided by Oracle, great, but not really what was asked.
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5. Describe the use of
PL/SQL tables Expected answer: PL/SQL tables are scalar arrays
that can be referenced by a binary integer. They can be used to hold
values for use in later queries or calculations. In Oracle 8 they will be
able to be of the %ROWTYPE designation, or RECORD.
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6. When is a declare
statement needed ? The DECLARE statement is used in PL/SQL
anonymous blocks such as with stand alone, non-stored PL/SQL procedures.
It must come first in a PL/SQL stand alone file if it is used.
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7. In what order should a
open/fetch/loop set of commands in a PL/SQL block be implemented if you
use the %NOTFOUND cursor variable in the exit when statement? Why?
Expected answer: OPEN then FETCH then LOOP followed by the exit
when. If not specified in this order will result in the final return being
done twice because of the way the %NOTFOUND is handled by PL/SQL.
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8. What are SQLCODE and
SQLERRM and why are they important for PL/SQL developers? Expected
answer: SQLCODE returns the value of the error number for the last error
encountered. The SQLERRM returns the actual error message for the last
error encountered. They can be used in exception handling to report, or,
store in an error log table, the error that occurred in the code. These
are especially useful for the WHEN OTHERS exception.
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9. How can you find
within a PL/SQL block, if a cursor is open? Expected answer: Use
the %ISOPEN cursor status variable.
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10. How can you generate debugging output
from PL/SQL? Expected answer: Use the DBMS_OUTPUT package. Another
possible method is to just use the SHOW ERROR command, but this only shows
errors. The DBMS_OUTPUT package can be used to show intermediate results
from loops and the status of variables as the procedure is executed. The
new package UTL_FILE can also be used.
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11. What are the types of triggers?
Expected Answer: There are 12 types of triggers in PL/SQL that
consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE,
DELETE and ALL key words: BEFORE ALL ROW INSERT AFTER ALL
ROW INSERT BEFORE INSERT AFTER INSERT etc.
1. Give one method for
transferring a table from one schema to another: There are several
possible methods, export-import, CREATE TABLE... AS SELECT, or COPY.
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2. What is the purpose of
the IMPORT option IGNORE? What is it?s default setting The IMPORT
IGNORE option tells import to ignore "already exists" errors. If it is not
specified the tables that already exist will be skipped. If it is
specified, the error is ignored and the tables data will be inserted. The
default value is N.
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3. You have a rollback
segment in a version 7.2 database that has expanded beyond optimal, how
can it be restored to optimal Use the ALTER TABLESPACE .....
SHRINK command.
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4. If the DEFAULT and
TEMPORARY tablespace clauses are left out of a CREATE USER command what
happens? Is this bad or good? Why The user is a*signed the SYSTEM
tablespace as a default and temporary tablespace. This is bad because it
causes user objects and temporary segments to be placed into the SYSTEM
tablespace resulting in fragmentation and improper table placement (only
data dictionary objects and the system rollback segment should be in
SYSTEM).
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5. What are some of the
Oracle provided packages that DBAs should be aware of Oracle
provides a number of packages in the form of the DBMS_ packages owned by
the SYS user. The packages used by DBAs may include: DBMS_SHARED_POOL,
DBMS_UTILITY, DBMS_SQL, DBMS_DDL, DBMS_SESSION, DBMS_OUTPUT and
DBMS_SNAPSHOT. They may also try to answer with the UTL*.SQL or CAT*.SQL
series of SQL procedures. These can be viewed as extra credit but aren?t
part of the answer.
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6. What happens if the
constraint name is left out of a constraint clause The Oracle
system will use the default name of SYS_Cxxxx where xxxx is a system
generated number. This is bad since it makes tracking which table the
constraint belongs to or what the constraint does harder.
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7. What happens if a
tablespace clause is left off of a primary key constraint clause
This results in the index that is automatically generated being
placed in then users default tablespace. Since this will usually be the
same tablespace as the table is being created in, this can cause serious
performance problems.
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8. What is the proper
method for disabling and re-enabling a primary key constraint You
use the ALTER TABLE command for both. However, for the enable clause you
must specify the USING INDEX and TABLESPACE clause for primary keys.
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9. What happens if a
primary key constraint is disabled and then enabled without fully
specifying the index clause The index is created in the user?s
default tablespace and all sizing information is lost. Oracle doesn?t
store this information as a part of the constraint definition, but only as
part of the index definition, when the constraint was disabled the index
was dropped and the information is gone.
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10. (On UNIX) When should more than one DB
writer process be used? How many should be used If the UNIX system
being used is capable of asynchronous IO then only one is required, if the
system is not capable of asynchronous IO then up to twice the number of
disks used by Oracle number of DB writers should be specified by use of
the db_writers initialization parameter.
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11. You are using hot backup without being
in archivelog mode, can you recover in the event of a failure? Why or why
not You can?t use hot backup without being in archivelog mode. So
no, you couldn?t recover.
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12. What causes the "snapshot too old"
error? How can this be prevented or mitigated This is caused by
large or long running transactions that have either wrapped onto their own
rollback space or have had another transaction write on part of their
rollback space. This can be prevented or mitigated by breaking the
transaction into a set of smaller transactions or increasing the size of
the rollback segments and their extents.
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13. How can you tell if a database object is invalid By
checking the status column of the DBA_, ALL_ or USER_OBJECTS views,
depending upon whether you own or only have permission on the view or are
using a DBA account.
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13. A user is getting an ORA-00942 error
yet you know you have granted them permission on the table, what else
should you check You need to check that the user has specified the
full name of the object (select empid from scott.emp; instead of select
empid from emp;) or has a synonym that balls to the object (create synonym
emp for scott.emp;)
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14. A developer is trying to create a view
and the database won?t let him. He has the "DEVELOPER" role which has the
"CREATE VIEW" system privilege and SELECT grants on the tables he is
using, what is the problem You need to verify the developer has
direct grants on all tables used in the view. You can?t create a stored
object with grants given through views.
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15. If you have an example table, what is
the best way to get sizing data for the production table implementation
The best way is to analyze the table and then use the data
provided in the DBA_TABLES view to get the average row length and other
pertinent data for the calculation. The quick and dirty way is to look at
the number of blocks the table is actually using and ratio the number of
rows in the table to its number of blocks against the number of expected
rows.
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16. How can you find out how many users are
currently logged into the database? How can you find their operating
system id There are several ways. One is to look at the v$session
or v$process views. Another way is to check the current_logins parameter
in the v$sysstat view. Another if you are on UNIX is to do a "ps -ef|grep
oracle|wc -l? command, but this only works against a single instance
installation.
------------------------------------------------------------
17. A user selects from a sequence and gets
back two values, his select is: SELECT pk_seq.nextval FROM
dual;What is the problem Somehow two values have been inserted
into the dual table. This table is a single row, single column table that
should only have one value in it.
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18. How can you determine if an index needs
to be dropped and rebuilt Run the ANALYZE INDEX command on the
index to validate its structure and then calculate the ratio of
LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near 1.0 (i.e. greater
than 0.7 or so) then the index should be rebuilt. Or if the ratio
BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3
1. How can variables be
parsed to a SQL routine By use of the & symbol. For pa*sing in
variables the numbers 1-8 can be used (&1, &2,...,&8) to pa*s
the values after the command into the SQLPLUS session. To be prompted for
a specific variable, place the ampersanded variable in the code itself:
"select * from dba_tables where owner=&owner_name;" . Use of
double ampersands tells SQLPLUS to resubstitute the value for each
subsequent use of the variable, a single ampersand will cause a reprompt
for the value unless an ACCEPT statement is used to get the value from the
user.
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2. You want to include a
carriage return/linefeed in your output from a SQL script, how can you do
this The best method is to use the CHR() function (CHR(10) is a
return/linefeed) and the concatenation function "||". Another method,
although it is hard to document and isn?t always portable is to use the
return/linefeed as a part of a quoted string.
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3. How can you call a
PL/SQL procedure from SQL By use of the EXECUTE (short form EXEC)
command.
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4. How do you execute a
host operating system command from within SQL By use of the
exclamation ball "!" (in UNIX and some other OS) or the HOST (HO) command.
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5. You want to use SQL to
build SQL, what is this called and give an example This is called
dynamic SQL. An example would be: set lines 90 pages 0 termout off
feedback off verify off spool drop_all.sql select ?drop
user ?||username||? cascade;? from dba_users where username not in
("SYS?,?SYSTEM?); spool off Essentially you are looking to
see that they know to include a command (in this case DROP
USER...CASCADE;) and that you need to concatenate using the ?||? the
values selected from the database.
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6. What SQLPlus command
is used to format output from a select This is best done with the
COLUMN command.
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7. You want to group the
following set of select returns, what can you group on
Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no
The only column that can be grouped on is the "item_no" column,
the rest have aggregate functions a*sociated with them.
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8. What special Oracle
feature allows you to specify how the cost based system treats a SQL
statement The COST based system allows the use of HINTs to control
the optimizer path selection. If they can give some example hints such as
FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better.
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9. You want to determine
the location of identical rows in a table before attempting to place a
unique index on the table, how can this be done Oracle tables
always have one guaranteed unique column, the rowid column. If you use a
min/max function against your rowid and then select against the proposed
primary key you can squeeze out the rowids of the duplicate rows pretty
quick. For example: select rowid from emp e where e.rowid
> (select min(x.rowid) from emp x where x.emp_no =
e.emp_no); In the situation where multiple columns make up the
proposed key, they must all be used in the where clause.
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10. What is a Cartesian product A
Cartesian product is the result of an unrestricted join of two or more
tables. The result set of a three table Cartesian product will have x * y
* z number of rows where x, y, z correspond to the number of rows in each
table involved in the join.
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11. You are joining a local and a remote table, the network
manager complains about the traffic involved, how can you reduce the
network traffic Push the processing of the remote data to the
remote instance by using a view to pre-select the information for the
join. This will result in only the data required for the join being sent
across.
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11. What is the default ordering of an
ORDER BY clause in a SELECT statement Ascending
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12. What is tkprof and how is it used
The tkprof tool is a tuning tool used to determine cpu and
execution times for SQL statements. You use it by first setting
timed_statistics to true in the initialization file and then turning on
tracing for either the entire database via the sql_trace parameter or for
the session using the ALTER SESSION command. Once the trace file is
generated you run the tkprof tool against the trace file and then look at
the output from the tkprof tool. This can also be used to generate explain
plan output.
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13. What is explain plan and how is it used
The EXPLAIN PLAN command is a tool to tune SQL statements. To use
it you must have an explain_table generated in the user you are running
the explain plan for. This is created using the utlxplan.sql script. Once
the explain plan table exists you run the explain plan command giving as
its argument the SQL statement to be explained. The explain_plan table is
then queried to see the execution plan of the statement. Explain plans can
also be run using tkprof.
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14. How do you set the number of lines on a
page of output? The width The SET command in SQLPLUS is used to
control the number of lines generated per page and the width of those
lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that
are 60 lines long with a line width of 80 characters. The PAGESIZE and
LINESIZE options can be shortened to PAGES and LINES.
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15. How do you prevent output from coming
to the screen The SET option TERMOUT controls output to the
screen. Setting TERMOUT OFF turns off screen output. This option can be
shortened to TERM.
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16. How do you prevent Oracle from giving
you informational messages during and after a SQL statement execution
The SET options FEEDBACK and VERIFY can be set to OFF.
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17. How do you generate file output from
SQL By use of the SPOOL command
1. A tablespace
has a table with 30 extents in it. Is this bad? Why or why not.
Multiple extents in and of themselves aren?t bad. However if you
also have chained rows this can hurt performance.
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2. How do you set up
tablespaces during an Oracle installation? You should always
attempt to use the Oracle Flexible Architecture standard or another
partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO
LOG, DATA, TEMPORARY and INDEX segments.
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3. You see multiple
fragments in the SYSTEM tablespace, what should you check first?
Ensure that users don?t have the SYSTEM tablespace as their
TEMPORARY or DEFAULT tablespace a*signment by checking the DBA_USERS view.
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4. What are some
indications that you need to increase the SHARED_POOL_SIZE parameter?
Poor data dictionary or library cache hit ratios, getting error
ORA-04031. Another indication is steadily decreasing performance with all
other tuning parameters the same.
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5. What is the general
guideline for sizing db_block_size and db_multi_block_read for an
application that does many full table scans? Oracle almost always
reads in 64k chunks. The two should have a product equal to 64 or a
multiple of 64.
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6. What is the fastest
query method for a table Fetch by rowid
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7. Explain the use of
TKPROF? What initialization parameter should be turned on to get full
TKPROF output? The tkprof tool is a tuning tool used to determine
cpu and execution times for SQL statements. You use it by first setting
timed_statistics to true in the initialization file and then turning on
tracing for either the entire database via the sql_trace parameter or for
the session using the ALTER SESSION command. Once the trace file is
generated you run the tkprof tool against the trace file and then look at
the output from the tkprof tool. This can also be used to generate explain
plan output.
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8. When looking at
v$sysstat you see that sorts (disk) is high. Is this bad or good? If bad
-How do you correct it? If you get excessive disk sorts this is
bad. This indicates you need to tune the sort area parameters in the
initialization files. The major sort are parameter is the SORT_AREA_SIZe
parameter.
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9. When should you
increase copy latches? What parameters control copy latches When
you get excessive contention for the copy latches as shown by the "redo
copy" latch hit ratio. You can increase copy latches via the
initialization parameter LOG_SIMULTANEOUS_COPIES to twice the number of
CPUs on your system.
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10. Where can you get a list of all
initialization parameters for your instance? How about an indication if
they are default settings or have been changed You can look in the
init.ora file for an indication of manually set parameters. For all
parameters, their value and whether or not the current value is the
default value, look in the v$parameter view.
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11. Describe hit ratio as it pertains to
the database buffers. What is the difference between instantaneous and
cumulative hit ratio and which should be used for tuning The hit
ratio is a measure of how many times the database was able to read a value
from the buffers verses how many times it had to re-read a data value from
the disks. A value greater than 80-90% is good, less could indicate
problems. If you simply take the ratio of existing parameters this will be
a cumulative value since the database started. If you do a comparison
between pairs of readings based on some arbitrary time span, this is the
instantaneous ratio for that time span. Generally speaking an
instantaneous reading gives more valuable data since it will tell you what
your instance is doing for the time it was generated over.
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12. Discuss row chaining, how does it
happen? How can you reduce it? How do you correct it Row chaining
occurs when a VARCHAR2 value is updated and the length of the new value is
longer than the old value and won?t fit in the remaining block space. This
results in the row chaining to another block. It can be reduced by setting
the storage parameters on the table to appropriate values. It can be
corrected by export and import of the effected table.
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13. When looking at the estat events report
you see that you are getting busy buffer waits. Is this bad? How can you
find what is causing it Buffer busy waits could indicate
contention in redo, rollback or data blocks. You need to check the
v$waitstat view to see what areas are causing the problem. The value of
the "count" column tells where the problem is, the "cla*s" column tells
you with what. UNDO is rollback segments, DATA is data base buffers.
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14. If you see contention for library
caches how can you fix it Increase the size of the shared pool.
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15. If you see statistics that deal with
"undo" what are they really talking about Rollback segments and
a*sociated structures.
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16. If a tablespace has a default
pctincrease of zero what will this cause (in relationship to the smon
process) The SMON process won?t automatically coalesce its free
space fragments.
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17. If a tablespace shows excessive
fragmentation what are some methods to defragment the tablespace? (7.1,7.2
and 7.3 only) In Oracle 7.0 to 7.2 The use of the 'alter session
set events 'immediate trace name coalesce level ts#';? command is the
easiest way to defragment contiguous free space fragmentation. The ts#
parameter corresponds to the ts# value found in the ts$ SYS table. In
version 7.3 the ?alter tablespace coalesce;? is best. If the free space
isn?t contiguous then export, drop and import of the tablespace contents
may be the only way to reclaim non-contiguous free space.
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18. How can you tell if a tablespace has
excessive fragmentation If a select against the dba_free_space
table shows that the count of a tablespaces extents is greater than the
count of its data files, then it is fragmented.
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19. You see the following on a status
report: redo log space requests 23 redo log space wait
time 0 Is this something to worry about? What if redo log space
wait time is high? How can you fix this Since the wait time is
zero, no. If the wait time was high it might indicate a need for more or
larger redo logs.
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20. What can cause a high value for
recursive calls? How can this be fixed A high value for recursive
calls is cause by improper cursor usage, excessive dynamic space
management actions, and or excessive statement re-parses. You need to
determine the cause and correct it By either relinking applications to
hold cursors, use proper space management techniques (proper storage and
sizing) or ensure repeat queries are placed in packages for proper reuse.
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21. If you see a pin hit ratio of less than
0.8 in the estat library cache report is this a problem? If so, how do you
fix it This indicate that the shared pool may be too small.
Increase the shared pool size.
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22. If you see the value for reloads is
high in the estat library cache report is this a matter for concern
Yes, you should strive for zero reloads if possible. If you see
excessive reloads then increase the size of the shared pool.
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23. You look at the dba_rollback_segs view
and see that there is a large number of shrinks and they are of relatively
small size, is this a problem? How can it be fixed if it is a problem
A large number of small shrinks indicates a need to increase the
size of the rollback segment extents. Ideally you should have no shrinks
or a small number of large shrinks. To fix this just increase the size of
the extents and adjust optimal accordingly.

24. You look at the
dba_rollback_segs view and see that you have a large number of wraps is
this a problem A large number of wraps indicates that your extent
size for your rollback segments are probably too small. Increase the size
of your extents to reduce the number of wraps. You can look at the average
transaction size in the same view to get the information on transaction
size.
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25. In a system with an average of 40
concurrent users you get the following from a query on rollback extents:
ROLLBACK CUR EXTENTS ---------------------
--------------------------
R01 11 R02 8 R03 12
R04 9 SYSTEM 4 26. You have
room for each to grow by 20 more extents each. Is there a problem? Should
you take any action No there is not a problem. You have 40 extents
showing and an average of 40 concurrent users. Since there is plenty of
room to grow no action is needed.
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27. You see multiple extents in the
temporary tablespace. Is this a problem As long as they are all
the same size this isn?t a problem. In fact, it can even improve
performance since Oracle won?t have to create a new extent when a user
needs one.
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28. Define OFA. OFA stands for
Optimal Flexible Architecture. It is a method of placing directories and
files in an Oracle system so that you get the maximum flexibility for
future tuning and file placement.
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29. How do you set up your tablespace on
installation The answer here should show an understanding of
separation of redo and rollback, data and indexes and isolation os SYSTEM
tables from other tables. An example would be to specify that at least 7
disks should be used for an Oracle installation so that you can place
SYSTEM tablespace on one, redo logs on two (mirrored redo logs) the
TEMPORARY tablespace on another, ROLLBACK tablespace on another and still
have two for DATA and INDEXES. They should indicate how they will handle
archive logs and exports as well. As long as they have a logical plan for
combining or further separation more or less disks can be specified.
--------------------------------------------------------------------------------
30. What should be done prior to installing
Oracle (for the OS and the disks) adjust kernel parameters or OS
tuning parameters in accordance with installation guide. Be sure enough
contiguous disk space is available.
--------------------------------------------------------------------------------
31. You have installed Oracle and you are
now setting up the actual instance. You have been waiting an hour for the
initialization script to finish, what should you check first to determine
if there is a problem Check to make sure that the archiver isn?t
stuck. If archive logging is turned on during install a large number of
logs will be created. This can fill up your archive log destination
causing Oracle to stop to wait for more space.
--------------------------------------------------------------------------------
32. When configuring SQLNET on the server
what files must be set up INITIALIZATION file, TNSNAMES.ORA file,
SQLNET.ORA file
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33. When configuring SQLNET on the client
what files need to be set up SQLNET.ORA, TNSNAMES.ORA
--------------------------------------------------------------------------------
34. What must be installed with ODBC on the
client in order for it to work with Oracle SQLNET and PROTOCOL
(for example: TCPIP adapter) layers of the transport programs.
--------------------------------------------------------------------------------
35. You have just started a new instance
with a large SGA on a busy existing server. Performance is terrible, what
should you check for The first thing to check with a large SGA is
that it isn?t being swapped out.
--------------------------------------------------------------------------------
36. What OS user should be used for the
first part of an Oracle installation (on UNIX) You must use root
first.
--------------------------------------------------------------------------------
37. When should the default values for
Oracle initialization parameters be used as is Never
--------------------------------------------------------------------------------
38. How many control files should you have?
Where should they be located At least 2 on separate disk spindles.
Be sure they say on separate disks, not just file systems.
--------------------------------------------------------------------------------
39. How many redo logs should you have and
how should they be configured for maximum recoverability You
should have at least three groups of two redo logs with the two logs each
on a separate disk spindle (mirrored by Oracle). The redo logs should not
be on raw devices on UNIX if it can be avoided.
--------------------------------------------------------------------------------
40. You have a simple application with no
"hot" tables (i.e. uniform IO and access requirements). How many disks
should you have a*suming standard layout for SYSTEM, USER, TEMP and
ROLLBACK tablespaces At least 7, see disk configuration answer
above.
--------------------------------------------------------------------------------
41. Describe third normal form
Something like: In third normal form all attributes in an entity
are related to the primary key and only to the primary key
--------------------------------------------------------------------------------
42. Is the following statement true or
false: "All relational databases must be in third normal form"
False. While 3NF is good for logical design most databases, if
they have more than just a few tables, will not perform well using full
3NF. Usually some entities will be denormalized in the logical to physical
transfer process.
--------------------------------------------------------------------------------
43. What is an ERD An ERD is an
Entity-Relationship-Diagram. It is used to show the entities and
relationships for a database logical model.
--------------------------------------------------------------------------------
44. Why are recursive relationships bad?
How do you resolve them A recursive relationship (one where a
table relates to itself) is bad when it is a hard relationship (i.e.
neither side is a "may" both are "must") as this can result in it not
being possible to put in a top or perhaps a bottom of the table (for
example in the EMPLOYEE table you couldn?t put in the PRESIDENT of the
company because he has no boss, or the junior janitor because he has no
subordinates). These type of relationships are usually resolved by adding
a small intersection entity.
--------------------------------------------------------------------------------
45. What does a hard one-to-one
relationship mean (one where the relationship on both ends is "must")
Expected answer: This means the two entities should probably be
made into one entity.
--------------------------------------------------------------------------------
46. How should a many-to-many relationship
be handled By adding an intersection entity table
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47. What is an artificial (derived) primary
key? When should an artificial (or derived) primary key be used A
derived key comes from a sequence. Usually it is used when a concatenated
key becomes too cumbersome to use as a foreign key.
--------------------------------------------------------------------------------
48. When should you consider
denormalization Whenever performance analysis indicates it would
be beneficial to do so without compromising data integrity.
--------------------------------------------------------------------------------
49. How can you determine if an Oracle
instance is up from the operating system level There are several
base Oracle processes that will be running on multi-user operating
systems, these will be smon, pmon, dbwr and lgwr. Any answer that has them
using their operating system process showing feature to check for these is
acceptable. For example, on UNIX a ps -ef|grep dbwr will show what
instances are up.
--------------------------------------------------------------------------------
50. Users from the PC clients are getting
messages indicating : ORA-06114: (Cnct err, can't get err txt. See
Servr Msgs & Codes Manual)
--------------------------------------------------------------------------------
What could the problem be The instance name is probably
incorrect in their connection string.
--------------------------------------------------------------------------------
51. Users from the PC clients are getting
the following error stack: ERROR: ORA-01034: ORACLE not available
ORA-07318: smsget: open error when opening sgadef.dbf file.
HP-UX Error: 2: No such file or directory
--------------------------------------------------------------------------------
What is the probable cause The Oracle instance is shutdown
that they are trying to access, restart the instance.
--------------------------------------------------------------------------------
52. How can you determine if the SQLNET
process is running for SQLNET V1? How about V2 For SQLNET V1 check
for the existence of the orasrv process. You can use the command "tcpctl
status" to get a full status of the V1 TCPIP server, other protocols have
similar command formats. For SQLNET V2 check for the presence of the
LISTENER process(s) or you can issue the command "lsnrctl status".
--------------------------------------------------------------------------------
53. What file will give you Oracle instance
status information? Where is it located The alert.ora log. It is
located in the directory specified by the background_dump_dest parameter
in the v$parameter table.
--------------------------------------------------------------------------------
54. Users aren?t being allowed on the
system. The following message is received: ORA-00257 archiver is
stuck. Connect internal only, until freed What is the problem
The archive destination is probably full, backup the archive logs
and remove them and the archiver will re-start.
--------------------------------------------------------------------------------
55. Where would you look to find out if a
redo log was corrupted a*suming you are using Oracle mirrored redo logs
There is no message that comes to the SQLDBA or SRVMGR programs
during startup in this situation, you must check the alert.log file for
this information.
--------------------------------------------------------------------------------
56. You attempt to add a datafile and get:
ORA-01118: cannot add anymore datafiles: limit of 40 exceeded
What is the problem and how can you fix it When the
database was created the db_files parameter in the initialization file was
set to 40. You can shutdown and reset this to a higher value, up to the
value of MAX_DATAFILES as specified at database creation. If the
MAX_DATAFILES is set to low, you will have to rebuild the control file to
increase it before proceeding.
--------------------------------------------------------------------------------
57. You look at your fragmentation report
and see that smon hasn?t coalesced any of you tablespaces, even though you
know several have large chunks of contiguous free extents. What is the
problem Check the dba_tablespaces view for the value of
pct_increase for the tablespaces. If pct_increase is zero, smon will not
coalesce their free space.
--------------------------------------------------------------------------------
58. Your users get the following error:
ORA-00055 maximum number of DML locks exceeded What is the
problem and how do you fix it The number of DML Locks is set by
the initialization parameter DML_LOCKS. If this value is set to low (which
it is by default) you will get this error. Increase the value of
DML_LOCKS. If you are sure that this is just a temporary problem, you can
have them wait and then try again later and the error should clear.
--------------------------------------------------------------------------------
59. You get a call from you backup DBA
while you are on vacation. He has corrupted all of the control files while
playing with the ALTER DATABASE BACKUP CONTROLFILE command. What do you do
As long as all datafiles are safe and he was successful with the
BACKUP controlfile command you can do the following: CONNECT
INTERNAL STARTUP MOUNT (Take any read-only tablespaces
offline before next step ALTER DATABASE DATAFILE .... OFFLINE;)
RECOVER DATABASE USING BACKUP CONTROLFILE ALTER DATABASE
OPEN RESETLOGS; (bring read-only tablespaces back online)
Shutdown and backup the system, then restart If they have
a recent output file from the ALTER DATABASE BACKUP CONTROL FILE TO TRACE;
command, they can use that to recover as well. If no backup of the
control file is available then the following will be required:
CONNECT INTERNAL STARTUP NOMOUNT CREATE CONTROL
FILE .....; However, they will need to know all of the datafiles,
logfiles, and settings for MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY,
MAXDATAFILES for the database to use the command.

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