what are the questions that are generally asked for a dba interview. if they are any sites which can help please list them out.
thanks in advance
dwaraka
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what are the questions that are generally asked for a dba interview. if they are any sites which can help please list them out.
thanks in advance
dwaraka
Mike Ault's "How to Hire (Or be Hired as) an Oracle DBA" is a good reference. Download the article from:
http://128.121.241.221/Pipelines/DBA...ves.htm#code02
HTH,
MIKE AULT’S INTERVIEW QUESTIONS FOR ORACLE, DBA, DEVELOPER CANDIDATES
Score each question on a 1-5 or 1-10 scale.
DBA SECTIONS: SQL/SQLPLUS, PL/SQL, TUNING, CONFIGURATION, TROUBLE SHOOTING
DEVELOPER SECTIONS: SQL/SQLPLUS, PL/SQL, DATA MODELING
DATA MODELER: DATA MODELING
ALL CANDIDATES FOR UNIX SHOP: UNIX
PL/SQL QUESTIONS:
1. Describe the difference between a procedure, function and anonymous pl/sql block.
Level: Low
Expected answer : Candidate should mention use of DECLARE statement, a function must return a value while a procedure doesn’t have to.
Score: ____________ Comment: ________________________________________________________
2. What is a mutating table error and how can you get around it?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
3. Describe the use of %ROWTYPE and %TYPE in PL/SQL
Level: Low
Expected answer: %ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type.
Score: ____________ Comment: ________________________________________________________
4. What packages (if any) has Oracle provided for use by developers?
Level: Intermediate to high
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.
Score: ____________ Comment: ________________________________________________________
5. Describe the use of PL/SQL tables
Level: Intermediate
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.
Score: ____________ Comment: ________________________________________________________
6. When is a declare statement needed ?
Level: Low
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.
Score: ____________ Comment: ________________________________________________________
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?
Level: Intermediate
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.
Score: ____________ Comment: ________________________________________________________
8. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
Level: Intermediate
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.
Score: ____________ Comment: ________________________________________________________
9. How can you find within a PL/SQL block, if a cursor is open?
Level: Low
Expected answer: Use the %ISOPEN cursor status variable.
Score: ____________ Comment: ________________________________________________________
10. How can you generate debugging output from PL/SQL?
Level:Intermediate to high
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.
Score: ____________ Comment: ________________________________________________________
11. What are the types of triggers?
Level:Intermediate to high
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.
Score: ____________ Comment: ________________________________________________________
Section average score: __________________________________ Level: __________________________
DBA:
1. Give one method for transferring a table from one schema to another:
Level:Intermediate
Expected Answer: There are several possible methods, export-import, CREATE TABLE... AS SELECT, or COPY.
Score: ____________ Comment: ________________________________________________________
2. What is the purpose of the IMPORT option IGNORE? What is it’s default setting?
Level: Low
Expected Answer: 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.
Score: ____________ Comment: ________________________________________________________
3. You have a rollback segment in a version 7.2 database that has expanded beyond optimal, how can it be restored to optimal?
Level: Low
Expected answer: Use the ALTER TABLESPACE ..... SHRINK command.
Score: ____________ Comment: ________________________________________________________
4. If the DEFAULT and TEMPORARY tablespace clauses are left out of a CREATE USER command what happens? Is this bad or good? Why?
Level: Low
Expected answer: The user is assigned 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).
Score: ____________ Comment: ________________________________________________________
5. What are some of the Oracle provided packages that DBAs should be aware of?
Level: Intermediate to High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
6. What happens if the constraint name is left out of a constraint clause?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
7. What happens if a tablespace clause is left off of a primary key constraint clause?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
8. What is the proper method for disabling and re-enabling a primary key constraint?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
9. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
10. (On UNIX) When should more than one DB writer process be used? How many should be used?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not?
Level: High
Expected answer: You can’t use hot backup without being in archivelog mode. So no, you couldn’t recover.
Score: ____________ Comment: ________________________________________________________
12. What causes the “snapshot too old” error? How can this be prevented or mitigated?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
13. How can you tell if a database object is invalid?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
14. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check?
Level: Low
Expected answer: 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 points to the object (create synonym emp for scott.emp;)
Score: ____________ Comment: ________________________________________________________
15. 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?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
16. If you have an example table, what is the best way to get sizing data for the production table implementation?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
17. How can you find out how many users are currently logged into the database? How can you find their operating system id?
Level: high
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
18. A user selects from a sequence and gets back two values, his select is:
SELECT pk_seq.nextval FROM dual;
What is the problem?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
19. How can you determine if an index needs to be dropped and rebuilt?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
Section average score: __________________________________ Level: __________________________
SQL/ SQLPLUS
1. How can variables be passed to a SQL routine?
Level: Low
Expected answer: By use of the & symbol. For passing in variables the numbers 1-8 can be used (&1, &2,...,&8) to pass 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.
Score: ____________ Comment: ________________________________________________________
2. You want to include a carriage return/linefeed in your output from a SQL script, how can you do this?
Level: Intermediate to high
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
3. How can you call a PL/SQL procedure from SQL?
Level: Intermediate
Expected answer: By use of the EXECUTE (short form EXEC) command.
Score: ____________ Comment: ________________________________________________________
4. How do you execute a host operating system command from within SQL?
Level: Low
Expected answer: By use of the exclamation point “!” (in UNIX and some other OS) or the HOST (HO) command.
Score: ____________ Comment: ________________________________________________________
5. You want to use SQL to build SQL, what is this called and give an example
Level: Intermediate to high
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
6. What SQLPlus command is used to format output from a select?
Level: low
Expected answer: This is best done with the COLUMN command.
Score: ____________ Comment: ________________________________________________________
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
Level: Intermediate
Expected answer: The only column that can be grouped on is the “item_no” column, the rest have aggregate functions associated with them.
Score: ____________ Comment: ________________________________________________________
8. What special Oracle feature allows you to specify how the cost based system treats a SQL statement?
Level: Intermediate to high
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
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?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
10. What is a Cartesian product?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
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?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
12. What is the default ordering of an ORDER BY clause in a SELECT statement?
Level: Low
Expected answer: Ascending
Score: ____________ Comment: ________________________________________________________
13. What is tkprof and how is it used?
Level: Intermediate to high
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
14. What is explain plan and how is it used?
Level: Intermediate to high
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
15. How do you set the number of lines on a page of output? The width?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
16. How do you prevent output from coming to the screen?
Level: Low
Expected answer: The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.
Score: ____________ Comment: ________________________________________________________
17. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution?
Level: Low
Expected answer: The SET options FEEDBACK and VERIFY can be set to OFF.
Score: ____________ Comment: ________________________________________________________
18. How do you generate file output from SQL?
Level: Low
Expected answer: By use of the SPOOL command
Score: ____________ Comment: ________________________________________________________
Section average score: __________________________________ Level: __________________________
TUNING QUESTIONS:
1. A tablespace has a table with 30 extents in it. Is this bad? Why or why not.
Level: Intermediate
Expected answer: Multiple extents in and of themselves aren’t bad. However if you also have chained rows this can hurt performance.
Score: ____________ Comment: ________________________________________________________
2. How do you set up tablespaces during an Oracle installation?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
3. You see multiple fragments in the SYSTEM tablespace, what should you check first?
Level: Low
Expected answer: Ensure that users don’t have the SYSTEM tablespace as their TEMPORARY or DEFAULT tablespace assignment by checking the DBA_USERS view.
Score: ____________ Comment: ________________________________________________________
4. What are some indications that you need to increase the SHARED_POOL_SIZE parameter?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
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?
Level: High
Expected answer: Oracle almost always reads in 64k chunks. The two should have a product equal to 64 or a multiple of 64.
Score: ____________ Comment: ________________________________________________________
6. What is the fastest query method for a table?
Level: Intermediate
Expected answer: Fetch by rowid
Score: ____________ Comment: ________________________________________________________
7. Explain the use of TKPROF? What initialization parameter should be turned on to get full TKPROF output?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
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?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
9. When should you increase copy latches? What parameters control copy latches?
Level: high
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
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?
Level: Low
Expected answer: 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$parameter view.
Score: ____________ Comment: ________________________________________________________
11. Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio and which should be used for tuning?
Level: Intermediate
Expected answer: The hit ratio is a measure of how many times the database was able to read a value from the buffers verses how many times it had to re-read a data value from the disks. A value greater than 80-90% is good, less could indicate problems. If you simply take the ratio of existing parameters this will be a cumulative value since the database started. If you do a comparison between pairs of readings based on some arbitrary time span, this is the instantaneous ratio for that time span. Generally speaking an instantaneous reading gives more valuable data since it will tell you what your instance is doing for the time it was generated over.
Score: ____________ Comment: ________________________________________________________
12. Discuss row chaining, how does it happen? How can you reduce it? How do you correct it?
Level: high
Expected answer: Row chaining occurs when a VARCHAR2 value is updated and the length of the new value is longer than the old value and won’t fit in the remaining block space. This results in the row chaining to another block. It can be reduced by setting the storage parameters on the table to appropriate values. It can be corrected by export and import of the effected table.
Score: ____________ Comment: ________________________________________________________
13. When looking at the estat events report you see that you are getting busy buffer waits. Is this bad? How can you find what is causing it?
Level: high
Expected answer: Buffer busy waits could indicate contention in redo, rollback or data blocks. You need to check the v$waitstat view to see what areas are causing the problem. The value of the “count” column tells where the problem is, the “class” column tells you with what. UNDO is rollback segments, DATA is data base buffers.
Score: ____________ Comment: ________________________________________________________
14. If you see contention for library caches how can you fix it?
Level: Intermediate
Expected answer: Increase the size of the shared pool.
Score: ____________ Comment: ________________________________________________________
15. If you see statistics that deal with “undo” what are they really talking about?
Level: Intermediate
Expected answer: Rollback segments and associated structures.
Score: ____________ Comment: ________________________________________________________
16. If a tablespace has a default pctincrease of zero what will this cause (in relationship to the smon process)?
Level: High
Expected answer: The SMON process won’t automatically coalesce its free space fragments.
Score: ____________ Comment: ________________________________________________________
17. If a tablespace shows excessive fragmentation what are some methods to defragment the tablespace? (7.1,7.2 and 7.3 only)
Level: High
Expected answer: 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 tablespacecoalesce;’ 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.
Score: ____________ Comment: ________________________________________________________
18. How can you tell if a tablespace has excessive fragmentation?
Level: Intermediate
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.
Score: ____________ Comment: ________________________________________________________
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?
Level: Intermediate
Expected answer: Since the wait time is zero, no. If the wait time was high it might indicate a need for more or larger redo logs.
Score: ____________ Comment: ________________________________________________________
20. What can cause a high value for recursive calls? How can this be fixed?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
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?
Level: Intermediate
Expected answer: This indicate that the shared pool may be too small. Increase the shared pool size.
Score: ____________ Comment: ________________________________________________________
22. If you see the value for reloads is high in the estat library cache report is this a matter for concern?
Level: Intermediate
Expected answer: Yes, you should strive for zero reloads if possible. If you see excessive reloads then increase the size of the shared pool.
Score: ____________ Comment: ________________________________________________________
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?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
24. You look at the dba_rollback_segs view and see that you have a large number of wraps is this a problem?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
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
You have room for each to grow by 20 more extents each. Is there a problem? Should you take any action?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
26. You see multiple extents in the temporary tablespace. Is this a problem?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
Section average score: __________________________________ Level: __________________________
INSTALLATION/CONFIGURATION
1. Define OFA.
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
2. How do you set up your tablespace on installation?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
3. What should be done prior to installing Oracle (for the OS and the disks)?
Level: Low
Expected Answer: adjust kernel parameters or OS tuning parameters in accordance with installation guide. Be sure enough contiguous disk space is available.
Score: ____________ Comment: ________________________________________________________
4. 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?
Level: Intermediate to high
Expected Answer: 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.
Score: ____________ Comment: ________________________________________________________
5. When configuring SQLNET on the server what files must be set up?
Level: Intermediate
Expected answer: INITIALIZATION file, TNSNAMES.ORA file, SQLNET.ORA file
Score: ____________ Comment: ________________________________________________________
6. When configuring SQLNET on the client what files need to be set up?
Level: Intermediate
Expected answer: SQLNET.ORA, TNSNAMES.ORA
Score: ____________ Comment: ________________________________________________________
7. What must be installed with ODBC on the client in order for it to work with Oracle?
Level: Intermediate
Expected answer: SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport programs.
Score: ____________ Comment: ________________________________________________________
8. You have just started a new instance with a large SGA on a busy existing server. Performance is terrible, what should you check for?
Level: Intermediate
Expected answer: The first thing to check with a large SGA is that it isn’t being swapped out.
Score: ____________ Comment: ________________________________________________________
9. What OS user should be used for the first part of an Oracle installation (on UNIX)?
Level: low
Expected answer: You must use root first.
Score: ____________ Comment: ________________________________________________________
10. When should the default values for Oracle initialization parameters be used as is?
Level: Low
Expected answer: Never
Score: ____________ Comment: ________________________________________________________
11. How many control files should you have? Where should they be located?
Level: Low
Expected answer: At least 2 on separate disk spindles. Be sure they say on separate disks, not just file systems.
Score: ____________ Comment: ________________________________________________________
12. How many redo logs should you have and how should they be configured for maximum recoverability?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
13. You have a simple application with no “hot” tables (i.e. uniform IO and access requirements). How many disks should you have assuming standard layout for SYSTEM, USER, TEMP and ROLLBACK tablespaces?
Expected answer: At least 7, see disk configuration answer above.
Score: ____________ Comment: ________________________________________________________
Section average score: __________________________________ Level: __________________________
DATA MODELER:
1. Describe third normal form?
Level: Low
Expected answer: Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key
Score: ____________ Comment: ________________________________________________________
2. Is the following statement true or false:
“All relational databases must be in third normal form”
Why or why not?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
3. What is an ERD?
Level: Low
Expected answer: An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model.
Score: ____________ Comment: ________________________________________________________
4. Why are recursive relationships bad? How do you resolve them?
Level: Intermediate
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.
Score: ____________ Comment: ________________________________________________________
5. What does a hard one-to-one relationship mean (one where the relationship on both ends is “must”)?
Level: Low to intermediate
Expected answer: This means the two entities should probably be made into one entity.
Score: ____________ Comment: ________________________________________________________
6. How should a many-to-many relationship be handled?
Level: Intermediate
Expected answer: By adding an intersection entity table
Score: ____________ Comment: ________________________________________________________
7. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used?
Level: Intermediate
Expected answer: A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key.
Score: ____________ Comment: ________________________________________________________
8. When should you consider denormalization?
Level: Intermediate
Expected answer: Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity.
Score: ____________ Comment: ________________________________________________________
Section average score: __________________________________ Level: __________________________
UNIX:
1. How can you determine the space left in a file system?
Level: Low
Expected answer: There are several commands to do this: du, df, or bdf
Score: ____________ Comment: ________________________________________________________
2. How can you determine the number of SQLNET users logged in to the UNIX system?
Level: Intermediate
Expected answer: SQLNET users will show up with a process unique name that begins with oracle, if you do a ps -ef|grep oracle |wc -l you can get a count of the number of users.
Score: ____________ Comment: ________________________________________________________
3. What command is used to type files to the screen?
Level: Low
Expected answer: cat, more, pg
Score: ____________ Comment: ________________________________________________________
4. What command is used to remove a file?
Level: Low
Expected answer: rm
Score: ____________ Comment: ________________________________________________________
5. Can you remove an open file under UNIX?
Level: Low
Expected answer: yes
Score: ____________ Comment: ________________________________________________________
6. How do you create a decision tree in a shell script?
Level: intermediate
Expected answer: depending on shell, usually a case-esac or an if-endif or fi structure
Score: ____________ Comment: ________________________________________________________
7. What is the purpose of the grep command?
Level: Low
Expected answer: grep is a string search command that parses the specified string from the specified file or files
Score: ____________ Comment: ________________________________________________________
8. The system has a program that always includes the word nocomp in its name, how can you determine the number of processes that are using this program?
Level: intermediate
Expected answer: ps -ef|grep *nocomp*|wc -l
Score: ____________ Comment: ________________________________________________________
9. What is an inode?
Level: Intermediate
Expected answer: an inode is a file status indicator. It is stored in both disk and memory and tracts file status. There is one inode for each file on the system.
Score: ____________ Comment: ________________________________________________________
10. The system administrator tells you that the system hasn’t been rebooted in 6 months, should he be proud of this?
Level: High
Expected answer: Maybe. Some UNIX systems don’t clean up well after themselves. Inode problems and dead user processes can accumulate causing possible performance and corruption problems. Most UNIX systems should have a scheduled periodic reboot so file systems can be checked and cleaned and dead or zombie processes cleared out.
Score: ____________ Comment: ________________________________________________________
11. What is redirection and how is it used?
Level: Intermediate
Expected answer: redirection is the process by which input or output to or from a process is redirected to another process. This can be done using the pipe symbol “|”, the greater than symbol “>“ or the “tee” command. This is one of the strengths of UNIX allowing the output from one command to be redirected directly into the input of another command.
Score: ____________ Comment: ________________________________________________________
12. How can you find dead processes?
Level: Intermediate
Expected answer: ps -ef|grep zombie -- or -- who -d depending on the system.
Score: ____________ Comment: ________________________________________________________
13. How can you find all the processes on your system?
Level: Low
Expected answer: Use the ps command
Score: ____________ Comment: ________________________________________________________
14. How can you find your id on a system?
Level: Low
Expected answer: Use the “who am i” command.
Score: ____________ Comment: ________________________________________________________
15. What is the finger command?
Level: Low
Expected answer: The finger command uses data in the passwd file to give information on system users.
Score: ____________ Comment: ________________________________________________________
16. What is the easiest method to create a file on UNIX?
Level: Low
Expected answer: Use the touch command
Score: ____________ Comment: ________________________________________________________
17. What does >> do?
Level: Intermediate
Expected answer: The “>>“ redirection symbol appends the output from the command specified into the file specified. The file must already have been created.
Score: ____________ Comment: ________________________________________________________
18. If you aren’t sure what command does a particular UNIX function what is the best way to determine the command?
Expected answer: The UNIX man -kcommand will search the man pages for the value specified. Review the results from the command to find the command of interest.
Score: ____________ Comment: ________________________________________________________
Section average score: __________________________________ Level: __________________________
ORACLE TROUBLESHOOTING:
1. How can you determine if an Oracle instance is up from the operating system level?
Level: Low
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
2. Users from the PC clients are getting messages indicating :
Level: Low
ORA-06114: (Cnct err, can't get err txt. See Servr Msgs & Codes Manual)
What could the problem be?
Expected answer: The instance name is probably incorrect in their connection string.
Score: ____________ Comment: ________________________________________________________
3. Users from the PC clients are getting the following error stack:
Level: Low
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?
Expected answer: The Oracle instance is shutdown that they are trying to access, restart the instance.
Score: ____________ Comment: ________________________________________________________
4. How can you determine if the SQLNET process is running for SQLNET V1? How about V2?
Level: Low
Expected answer: 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”.
Score: ____________ Comment: ________________________________________________________
5. What file will give you Oracle instance status information? Where is it located?
Level: Low
Expected answer: The alert.ora log. It is located in the directory specified by the background_dump_dest parameter in the v$parameter table.
6. Users aren’t being allowed on the system. The following message is received:
Level: Intermediate
ORA-00257 archiver is stuck. Connect internal only, until freed
What is the problem?
Expected answer: The archive destination is probably full, backup the archive logs and remove them and the archiver will re-start.
Score: ____________ Comment: ________________________________________________________
7. Where would you look to find out if a redo log was corrupted assuming you are using Oracle mirrored redo logs?
Level: Intermediate
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
8. You attempt to add a datafile and get:
Level: Intermediate
ORA-01118: cannot add anymore datafiles: limit of 40 exceeded
What is the problem and how can you fix it?
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
9. 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?
Level: High
Expected answer: 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.
Score: ____________ Comment: ________________________________________________________
10. Your users get the following error:
Level: Intermediate
ORA-00055 maximum number of DML locks exceeded
What is the problem and how do you fix it?
Expected answer: 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.
Score: _________ Comment: ________________________________________________________
11. 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?
Level: High
Expected answer: 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.
Score: __________ Comment: ________________________________________________________
Section average score: ______________________________ Level: __________________________
ORACLE CANDIDATE INTERVIEW RESULTS
Interview average score: _____________________________ Level: _________________________
Comments: