Why do you use Option Explicit?
What are the commonly used data types in VBScript?
What is a session object?
What are the three objects of ADO?
What are the lock-types available in ADO? Explain.
What are the cursor types available in ADO? Explain.
What is a COM component?
How do you register a COM component?
What is a virtual root and how do you create one?
What is a database index, how do you create one, discuss its pros and cons?
How do you use multiple record sets (rs.NextRecordSet)?
As soon as you fetch a record set, what operations would you perform?
Define a transaction. What are ACID properties of a transaction?
How would you remotely administer IIS?
What is RAID? What is it used for?
What is normalization? Explain normalization types.
What is the disadvantage of creating an index in every column of a database table?
What are the uses of source control software?
You have a query that runs slowly, how would you make it better? How would you make it better in .NET environment?
What is a bit datatype? What is it used for?
How would you go about securing IIS and MS-SQL Server?
What is the difference between Request(”field”) and Request.Form(”field”)?
Friday, November 23, 2007
UNIX INTREVIEW QUESTIONS
Question 1: What is the major advantage of a hash table?
Answer: The major advantage of a hash table is its speed. Because the hash function is to take a range of key values and transform them into index values in such a way that the key values are distributed randomly across all the indices of a hash table.
Question 2: What are the techniques that you use to handle the collisions in hash tables?
Answer: We can use two major techniques to handle the collisions. They are open addressing and separate chaining. In open addressing, data items that hash to a full array cell are placed in another cell in the array. In separate chaining, each array element consist of a linked list. All data items hashing to a given array index are inserted in that list.
Question 3: In Unix OS, what is the file server?
Answer: The file server is a machine that shares its disk storage and files with other machines on the network.
Question 4: What is NFS? What is its job?
Answer: NFS stands for Network File System. NFS enables filesystems physically residing on one computer system to be used by other computers in the network, appearing to users on the remote host as just another local disk.
Question 5: What is CVS? List some useful CVS commands
Anser: CVS is Concurrent Version System. It is the front end to the RCS revision control system which extends the notion of revision control from a collection of files in a single directory to a hierarchical collection of directories consisting of revision controlled files. These directories and files can be combined together to form a software release.
There are some useful commands that are being used very often. They are
cvs checkout
cvs update
cvs add
cvs remove
cvs commit
Answer: The major advantage of a hash table is its speed. Because the hash function is to take a range of key values and transform them into index values in such a way that the key values are distributed randomly across all the indices of a hash table.
Question 2: What are the techniques that you use to handle the collisions in hash tables?
Answer: We can use two major techniques to handle the collisions. They are open addressing and separate chaining. In open addressing, data items that hash to a full array cell are placed in another cell in the array. In separate chaining, each array element consist of a linked list. All data items hashing to a given array index are inserted in that list.
Question 3: In Unix OS, what is the file server?
Answer: The file server is a machine that shares its disk storage and files with other machines on the network.
Question 4: What is NFS? What is its job?
Answer: NFS stands for Network File System. NFS enables filesystems physically residing on one computer system to be used by other computers in the network, appearing to users on the remote host as just another local disk.
Question 5: What is CVS? List some useful CVS commands
Anser: CVS is Concurrent Version System. It is the front end to the RCS revision control system which extends the notion of revision control from a collection of files in a single directory to a hierarchical collection of directories consisting of revision controlled files. These directories and files can be combined together to form a software release.
There are some useful commands that are being used very often. They are
cvs checkout
cvs update
cvs add
cvs remove
cvs commit
Monday, November 19, 2007
IMPORTANT QUERIES
1.This script will spell out numbers to words
select decode( sign( &num ), -1, 'Negative ', 0, 'Zero', NULL ) ||
decode( sign( abs(&num) ), +1, to_char( to_date( abs(&num),'J'),'Jsp') )
from dual
/
2. Select the Nth highest value from a table
select level, max('col_name') from my_table
where level = '&n'
connect by prior ('col_name') > 'col_name')
group by level;
3. Example of a CROSS MATRIX report
SELECT job,
sum(decode(deptno,10,sal)) DEPT10,
sum(decode(deptno,20,sal)) DEPT20,
sum(decode(deptno,30,sal)) DEPT30,
sum(decode(deptno,40,sal)) DEPT40
FROM scott.emp
GROUP BY job
/
5.Select the Nth lowest value from a table
select level, min('col_name') from my_table
where level = '&n'
connect by prior ('col_name') < 'col_name')
group by level;
6. Handy for huge tables that cause rollback segment problems
declare
i number := 0;
cursor s1 is SELECT rowid, t.* FROM tab1 t WHERE col1 = 'value1';
begin
for c1 in s1 loop
update tab1 set col1 = 'value2'
where rowid = c1.rowid;
i := i + 1; -- Commit after every X records
if i > 10000 then
commit;
i := 0;
end if;
end loop;
commit;
end;
/
7.Simple password encryption package to demonstrate how
CREATE OR REPLACE PACKAGE PASSWORD AS
function encrypt(i_password varchar2) return varchar2;
function decrypt(i_password varchar2) return varchar2;
END PASSWORD;
/
show errors
CREATE OR REPLACE PACKAGE BODY PASSWORD AS
-- key must be exactly 8 bytes long
c_encrypt_key varchar2(8) := 'key45678';
function encrypt (i_password varchar2) return varchar2 is
v_encrypted_val varchar2(38);
v_data varchar2(38);
begin
-- Input data must have a length divisible by eight
v_data := RPAD(i_password,(TRUNC(LENGTH(i_password)/8)+1)*8,CHR(0));
DBMS_OBFUSCATION_TOOLKIT.DESENCRYPT(
input_string => v_data,
key_string => c_encrypt_key,
encrypted_string => v_encrypted_val);
return v_encrypted_val;
end encrypt;
function decrypt (i_password varchar2) return varchar2 is
v_decrypted_val varchar2(38);
begin
DBMS_OBFUSCATION_TOOLKIT.DESDECRYPT(
input_string => i_password,
key_string => c_encrypt_key,
decrypted_string => v_decrypted_val);
return v_decrypted_val;
end decrypt;
end PASSWORD;
8. Send e-mail messages from PL/SQL
CREATE OR REPLACE PROCEDURE SEND_MAIL (
msg_from varchar2 := 'oracle',
msg_to varchar2,
msg_subject varchar2 := 'E-Mail message from your database',
msg_text varchar2 := '' )
IS
c utl_tcp.connection;
rc integer;
BEGIN
c := utl_tcp.open_connection('127.0.0.1', 25); -- open the SMTP port 25 on local machine
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'HELO localhost');
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'MAIL FROM: '||msg_from);
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'RCPT TO: '||msg_to);
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'DATA'); -- Start message body
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'Subject: '||msg_subject);
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, msg_text);
rc := utl_tcp.write_line(c, '.'); -- End of message body
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'QUIT');
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
utl_tcp.close_connection(c); -- Close the connection
EXCEPTION
when others then
raise_application_error(
-20000, 'Unable to send e-mail message from pl/sql because of: '||
sqlerrm);
END;
/
8. Send e-mail messages and attachments from PL/SQL
CREATE OR REPLACE PROCEDURE SEND_MAIL (
msg_from varchar2 := 'EMAILADDRESS@DOMAIN.COM', ----- MAIL BOX SENDING THE EMAIL
msg_to varchar2 := 'EMAILADDRESS@DOMAIN.COM', ----- MAIL BOX RECIEVING THE EMAIL
msg_subject varchar2 := 'Output file TEST1', ----- EMAIL SUBJECT
msg_text varchar2 := 'THIS IS THE TEXT OF THE EMAIL MESSAGE.',
v_output1 varchar2 := 'THIS IS THE TEXT OF THE ATTACHMENT FILE. THIS TEXT SHOULD BE IN A TEXT FILE ATTACHED TO THE EMAIL.')
IS
c utl_tcp.connection;
rc integer;
crlf VARCHAR2(2):= CHR(13)||CHR(10);
mesg VARCHAR2( 32767 );
BEGIN
c := utl_tcp.open_connection('196.35.140.18', 25); ----- OPEN SMTP PORT CONNECTION
rc := utl_tcp.write_line(c, 'HELO 196.35.140.18'); ----- PERFORMS HANDSHAKING WITH SMTP SERVER
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'EHLO 196.35.140.18'); ----- PERFORMS HANDSHAKING WITH SMTP SERVER, INCLUDING EXTRA INFORMATION
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'MAIL FROM: '||msg_from); ----- MAIL BOX SENDING THE EMAIL
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'RCPT TO: '||msg_to); ----- MAIL BOX RECIEVING THE EMAIL
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'DATA'); ----- EMAIL MESSAGE BODY START
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'Date: '||TO_CHAR( SYSDATE, 'dd Mon yy hh24:mi:ss' ));
rc := utl_tcp.write_line(c, 'From: '||msg_from||' <'||msg_from||'>');
rc := utl_tcp.write_line(c, 'MIME-Version: 1.0');
rc := utl_tcp.write_line(c, 'To: '||msg_to||' <'||msg_to||'>');
rc := utl_tcp.write_line(c, 'Subject: '||msg_subject);
rc := utl_tcp.write_line(c, 'Content-Type: multipart/mixed;'); ----- INDICATES THAT THE BODY CONSISTS OF MORE THAN ONE PART
rc := utl_tcp.write_line(c, ' boundary="-----SECBOUND"'); ----- SEPERATOR USED TO SEPERATE THE BODY PARTS
rc := utl_tcp.write_line(c, ''); ----- INSERTS A BLANK LINE. PART OF THE MIME FORMAT AND NONE OF THEM SHOULD BE REMOVED.
rc := utl_tcp.write_line(c, '-------SECBOUND');
rc := utl_tcp.write_line(c, 'Content-Type: text/plain'); ----- 1ST BODY PART. EMAIL TEXT MESSAGE
rc := utl_tcp.write_line(c, 'Content-Transfer-Encoding: 7bit');
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, msg_text); ----- TEXT OF EMAIL MESSAGE
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, '-------SECBOUND');
rc := utl_tcp.write_line(c, 'Content-Type: text/plain;'); ----- 2ND BODY PART.
rc := utl_tcp.write_line(c, ' name="Test.txt"');
rc := utl_tcp.write_line(c, 'Content-Transfer_Encoding: 8bit');
rc := utl_tcp.write_line(c, 'Content-Disposition: attachment;'); ----- INDICATES THAT THIS IS AN ATTACHMENT
rc := utl_tcp.write_line(c, ' filename="Test.txt"'); ----- SUGGESTED FILE NAME FOR ATTACHMENT
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, v_output1);
rc := utl_tcp.write_line(c, '-------SECBOUND--');
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, '.'); ----- EMAIL MESSAGE BODY END
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'QUIT'); ----- ENDS EMAIL TRANSACTION
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
utl_tcp.close_connection(c); ----- CLOSE SMTP PORT CONNECTION
EXCEPTION
when others then
raise_application_error(-20000, SQLERRM);
END;
/
9. Access Internet Web pages from SQL or PL/SQL
select utl_http.request('http://www.orafaq.net/') from dual
10. Script to create a new user (with privs) like an existing trem
database user. User data will not be copied.
set pages 0 feed off veri off lines 500
accept oldname prompt "Enter user to model new user to: "
accept newname prompt "Enter new user name: "
-- accept psw prompt "Enter new user's password: "
-- Create user...
select 'create user &&newname identified by values '''||password||''''||
-- select 'create user &&newname identified by &psw'||
' default tablespace '||default_tablespace||
' temporary tablespace '||temporary_tablespace||' profile '||
profile||';'
from sys.dba_users
where username = upper('&&oldname');
-- Grant Roles...
select 'grant '||granted_role||' to &&newname'||
decode(ADMIN_OPTION, 'YES', ' WITH ADMIN OPTION')||';'
from sys.dba_role_privs
where grantee = upper('&&oldname');
-- Grant System Privs...
select 'grant '||privilege||' to &&newname'||
decode(ADMIN_OPTION, 'YES', ' WITH ADMIN OPTION')||';'
from sys.dba_sys_privs
where grantee = upper('&&oldname');
-- Grant Table Privs...
select 'grant '||privilege||' on '||owner||'.'||table_name||' to &&newname;'
from sys.dba_tab_privs
where grantee = upper('&&oldname');
-- Grant Column Privs...
select 'grant '||privilege||' on '||owner||'.'||table_name||
'('||column_name||') to &&newname;'
from sys.dba_col_privs
where grantee = upper('&&oldname');
-- Tablespace Quotas...
select 'alter user '||username||' quota '||
    decode(max_bytes, -1, 'UNLIMITED', max_bytes)||
    ' on '||tablespace_name||';'
from  sys.dba_ts_quotas
where  username = upper('&&oldname');
-- Set Default Role...
set serveroutput on
declare
defroles varchar2(4000);
begin
for c1 in (select * from sys.dba_role_privs
where grantee = upper('&&oldname')
and default_role = 'YES'
) loop
if length(defroles) > 0 then
defroles := defroles||','||c1.granted_role;
else
defroles := defroles||c1.granted_role;
end if;
end loop;
dbms_output.put_line('alter user &&newname default role '||defroles||';');
end;
/
11. Tabular display of redo-log archiving history (logs/hour)
set pagesize 50000
set veri off
set colsep ""
set termout off
def time="time"
col time new_value time
select 'to_char(first_time,''DD/MM/YY HH24:MI:SS'')' time
from dual
where &&_O_RELEASE like '8%' -- Oracle8
/
set termout on
select substr(&&time, 1, 5) day,
to_char(sum(decode(substr(&&time,10,2),'00',1,0)),'99') "00",
to_char(sum(decode(substr(&&time,10,2),'01',1,0)),'99') "01",
to_char(sum(decode(substr(&&time,10,2),'02',1,0)),'99') "02",
to_char(sum(decode(substr(&&time,10,2),'03',1,0)),'99') "03",
to_char(sum(decode(substr(&&time,10,2),'04',1,0)),'99') "04",
to_char(sum(decode(substr(&&time,10,2),'05',1,0)),'99') "05",
to_char(sum(decode(substr(&&time,10,2),'06',1,0)),'99') "06",
to_char(sum(decode(substr(&&time,10,2),'07',1,0)),'99') "07",
to_char(sum(decode(substr(&&time,10,2),'08',1,0)),'99') "08",
to_char(sum(decode(substr(&&time,10,2),'09',1,0)),'99') "09",
to_char(sum(decode(substr(&&time,10,2),'10',1,0)),'99') "10",
to_char(sum(decode(substr(&&time,10,2),'11',1,0)),'99') "11",
to_char(sum(decode(substr(&&time,10,2),'12',1,0)),'99') "12",
to_char(sum(decode(substr(&&time,10,2),'13',1,0)),'99') "13",
to_char(sum(decode(substr(&&time,10,2),'14',1,0)),'99') "14",
to_char(sum(decode(substr(&&time,10,2),'15',1,0)),'99') "15",
to_char(sum(decode(substr(&&time,10,2),'16',1,0)),'99') "16",
to_char(sum(decode(substr(&&time,10,2),'17',1,0)),'99') "17",
to_char(sum(decode(substr(&&time,10,2),'18',1,0)),'99') "18",
to_char(sum(decode(substr(&&time,10,2),'19',1,0)),'99') "19",
to_char(sum(decode(substr(&&time,10,2),'20',1,0)),'99') "20",
to_char(sum(decode(substr(&&time,10,2),'21',1,0)),'99') "21",
to_char(sum(decode(substr(&&time,10,2),'22',1,0)),'99') "22",
to_char(sum(decode(substr(&&time,10,2),'23',1,0)),'99') "23"
from sys.v_$log_history
group by substr(&&time,1,5)
/
set colsep " "
12. Compare indexes on two databases and list the differences
col table_name format a30
col column_name format a30
col column_position format 990
accept DB1 prompt "Enter database name to compare from: "
accept DB2 prompt "Enter database name to compare to: "
13. Tables/ columns with indexes on &DB1 that's not on &DB2
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB1.
where table_owner not in ('SYS', 'SYSTEM')
minus
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB2.
where table_owner not in ('SYS', 'SYSTEM')
/
14. Tables/ columns with indexes on &DB2 that's not on &DB1
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB2.
where table_owner not in ('SYS', 'SYSTEM')
minus
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB1.
where table_owner not in ('SYS', 'SYSTEM')
/
spool off
select decode( sign( &num ), -1, 'Negative ', 0, 'Zero', NULL ) ||
decode( sign( abs(&num) ), +1, to_char( to_date( abs(&num),'J'),'Jsp') )
from dual
/
2. Select the Nth highest value from a table
select level, max('col_name') from my_table
where level = '&n'
connect by prior ('col_name') > 'col_name')
group by level;
3. Example of a CROSS MATRIX report
SELECT job,
sum(decode(deptno,10,sal)) DEPT10,
sum(decode(deptno,20,sal)) DEPT20,
sum(decode(deptno,30,sal)) DEPT30,
sum(decode(deptno,40,sal)) DEPT40
FROM scott.emp
GROUP BY job
/
5.Select the Nth lowest value from a table
select level, min('col_name') from my_table
where level = '&n'
connect by prior ('col_name') < 'col_name')
group by level;
6. Handy for huge tables that cause rollback segment problems
declare
i number := 0;
cursor s1 is SELECT rowid, t.* FROM tab1 t WHERE col1 = 'value1';
begin
for c1 in s1 loop
update tab1 set col1 = 'value2'
where rowid = c1.rowid;
i := i + 1; -- Commit after every X records
if i > 10000 then
commit;
i := 0;
end if;
end loop;
commit;
end;
/
7.Simple password encryption package to demonstrate how
CREATE OR REPLACE PACKAGE PASSWORD AS
function encrypt(i_password varchar2) return varchar2;
function decrypt(i_password varchar2) return varchar2;
END PASSWORD;
/
show errors
CREATE OR REPLACE PACKAGE BODY PASSWORD AS
-- key must be exactly 8 bytes long
c_encrypt_key varchar2(8) := 'key45678';
function encrypt (i_password varchar2) return varchar2 is
v_encrypted_val varchar2(38);
v_data varchar2(38);
begin
-- Input data must have a length divisible by eight
v_data := RPAD(i_password,(TRUNC(LENGTH(i_password)/8)+1)*8,CHR(0));
DBMS_OBFUSCATION_TOOLKIT.DESENCRYPT(
input_string => v_data,
key_string => c_encrypt_key,
encrypted_string => v_encrypted_val);
return v_encrypted_val;
end encrypt;
function decrypt (i_password varchar2) return varchar2 is
v_decrypted_val varchar2(38);
begin
DBMS_OBFUSCATION_TOOLKIT.DESDECRYPT(
input_string => i_password,
key_string => c_encrypt_key,
decrypted_string => v_decrypted_val);
return v_decrypted_val;
end decrypt;
end PASSWORD;
8. Send e-mail messages from PL/SQL
CREATE OR REPLACE PROCEDURE SEND_MAIL (
msg_from varchar2 := 'oracle',
msg_to varchar2,
msg_subject varchar2 := 'E-Mail message from your database',
msg_text varchar2 := '' )
IS
c utl_tcp.connection;
rc integer;
BEGIN
c := utl_tcp.open_connection('127.0.0.1', 25); -- open the SMTP port 25 on local machine
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'HELO localhost');
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'MAIL FROM: '||msg_from);
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'RCPT TO: '||msg_to);
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'DATA'); -- Start message body
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'Subject: '||msg_subject);
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, msg_text);
rc := utl_tcp.write_line(c, '.'); -- End of message body
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'QUIT');
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
utl_tcp.close_connection(c); -- Close the connection
EXCEPTION
when others then
raise_application_error(
-20000, 'Unable to send e-mail message from pl/sql because of: '||
sqlerrm);
END;
/
8. Send e-mail messages and attachments from PL/SQL
CREATE OR REPLACE PROCEDURE SEND_MAIL (
msg_from varchar2 := 'EMAILADDRESS@DOMAIN.COM', ----- MAIL BOX SENDING THE EMAIL
msg_to varchar2 := 'EMAILADDRESS@DOMAIN.COM', ----- MAIL BOX RECIEVING THE EMAIL
msg_subject varchar2 := 'Output file TEST1', ----- EMAIL SUBJECT
msg_text varchar2 := 'THIS IS THE TEXT OF THE EMAIL MESSAGE.',
v_output1 varchar2 := 'THIS IS THE TEXT OF THE ATTACHMENT FILE. THIS TEXT SHOULD BE IN A TEXT FILE ATTACHED TO THE EMAIL.')
IS
c utl_tcp.connection;
rc integer;
crlf VARCHAR2(2):= CHR(13)||CHR(10);
mesg VARCHAR2( 32767 );
BEGIN
c := utl_tcp.open_connection('196.35.140.18', 25); ----- OPEN SMTP PORT CONNECTION
rc := utl_tcp.write_line(c, 'HELO 196.35.140.18'); ----- PERFORMS HANDSHAKING WITH SMTP SERVER
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'EHLO 196.35.140.18'); ----- PERFORMS HANDSHAKING WITH SMTP SERVER, INCLUDING EXTRA INFORMATION
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'MAIL FROM: '||msg_from); ----- MAIL BOX SENDING THE EMAIL
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'RCPT TO: '||msg_to); ----- MAIL BOX RECIEVING THE EMAIL
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'DATA'); ----- EMAIL MESSAGE BODY START
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'Date: '||TO_CHAR( SYSDATE, 'dd Mon yy hh24:mi:ss' ));
rc := utl_tcp.write_line(c, 'From: '||msg_from||' <'||msg_from||'>');
rc := utl_tcp.write_line(c, 'MIME-Version: 1.0');
rc := utl_tcp.write_line(c, 'To: '||msg_to||' <'||msg_to||'>');
rc := utl_tcp.write_line(c, 'Subject: '||msg_subject);
rc := utl_tcp.write_line(c, 'Content-Type: multipart/mixed;'); ----- INDICATES THAT THE BODY CONSISTS OF MORE THAN ONE PART
rc := utl_tcp.write_line(c, ' boundary="-----SECBOUND"'); ----- SEPERATOR USED TO SEPERATE THE BODY PARTS
rc := utl_tcp.write_line(c, ''); ----- INSERTS A BLANK LINE. PART OF THE MIME FORMAT AND NONE OF THEM SHOULD BE REMOVED.
rc := utl_tcp.write_line(c, '-------SECBOUND');
rc := utl_tcp.write_line(c, 'Content-Type: text/plain'); ----- 1ST BODY PART. EMAIL TEXT MESSAGE
rc := utl_tcp.write_line(c, 'Content-Transfer-Encoding: 7bit');
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, msg_text); ----- TEXT OF EMAIL MESSAGE
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, '-------SECBOUND');
rc := utl_tcp.write_line(c, 'Content-Type: text/plain;'); ----- 2ND BODY PART.
rc := utl_tcp.write_line(c, ' name="Test.txt"');
rc := utl_tcp.write_line(c, 'Content-Transfer_Encoding: 8bit');
rc := utl_tcp.write_line(c, 'Content-Disposition: attachment;'); ----- INDICATES THAT THIS IS AN ATTACHMENT
rc := utl_tcp.write_line(c, ' filename="Test.txt"'); ----- SUGGESTED FILE NAME FOR ATTACHMENT
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, v_output1);
rc := utl_tcp.write_line(c, '-------SECBOUND--');
rc := utl_tcp.write_line(c, '');
rc := utl_tcp.write_line(c, '.'); ----- EMAIL MESSAGE BODY END
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
rc := utl_tcp.write_line(c, 'QUIT'); ----- ENDS EMAIL TRANSACTION
dbms_output.put_line(utl_tcp.get_line(c, TRUE));
utl_tcp.close_connection(c); ----- CLOSE SMTP PORT CONNECTION
EXCEPTION
when others then
raise_application_error(-20000, SQLERRM);
END;
/
9. Access Internet Web pages from SQL or PL/SQL
select utl_http.request('http://www.orafaq.net/') from dual
10. Script to create a new user (with privs) like an existing trem
database user. User data will not be copied.
set pages 0 feed off veri off lines 500
accept oldname prompt "Enter user to model new user to: "
accept newname prompt "Enter new user name: "
-- accept psw prompt "Enter new user's password: "
-- Create user...
select 'create user &&newname identified by values '''||password||''''||
-- select 'create user &&newname identified by &psw'||
' default tablespace '||default_tablespace||
' temporary tablespace '||temporary_tablespace||' profile '||
profile||';'
from sys.dba_users
where username = upper('&&oldname');
-- Grant Roles...
select 'grant '||granted_role||' to &&newname'||
decode(ADMIN_OPTION, 'YES', ' WITH ADMIN OPTION')||';'
from sys.dba_role_privs
where grantee = upper('&&oldname');
-- Grant System Privs...
select 'grant '||privilege||' to &&newname'||
decode(ADMIN_OPTION, 'YES', ' WITH ADMIN OPTION')||';'
from sys.dba_sys_privs
where grantee = upper('&&oldname');
-- Grant Table Privs...
select 'grant '||privilege||' on '||owner||'.'||table_name||' to &&newname;'
from sys.dba_tab_privs
where grantee = upper('&&oldname');
-- Grant Column Privs...
select 'grant '||privilege||' on '||owner||'.'||table_name||
'('||column_name||') to &&newname;'
from sys.dba_col_privs
where grantee = upper('&&oldname');
-- Tablespace Quotas...
select 'alter user '||username||' quota '||
    decode(max_bytes, -1, 'UNLIMITED', max_bytes)||
    ' on '||tablespace_name||';'
from  sys.dba_ts_quotas
where  username = upper('&&oldname');
-- Set Default Role...
set serveroutput on
declare
defroles varchar2(4000);
begin
for c1 in (select * from sys.dba_role_privs
where grantee = upper('&&oldname')
and default_role = 'YES'
) loop
if length(defroles) > 0 then
defroles := defroles||','||c1.granted_role;
else
defroles := defroles||c1.granted_role;
end if;
end loop;
dbms_output.put_line('alter user &&newname default role '||defroles||';');
end;
/
11. Tabular display of redo-log archiving history (logs/hour)
set pagesize 50000
set veri off
set colsep ""
set termout off
def time="time"
col time new_value time
select 'to_char(first_time,''DD/MM/YY HH24:MI:SS'')' time
from dual
where &&_O_RELEASE like '8%' -- Oracle8
/
set termout on
select substr(&&time, 1, 5) day,
to_char(sum(decode(substr(&&time,10,2),'00',1,0)),'99') "00",
to_char(sum(decode(substr(&&time,10,2),'01',1,0)),'99') "01",
to_char(sum(decode(substr(&&time,10,2),'02',1,0)),'99') "02",
to_char(sum(decode(substr(&&time,10,2),'03',1,0)),'99') "03",
to_char(sum(decode(substr(&&time,10,2),'04',1,0)),'99') "04",
to_char(sum(decode(substr(&&time,10,2),'05',1,0)),'99') "05",
to_char(sum(decode(substr(&&time,10,2),'06',1,0)),'99') "06",
to_char(sum(decode(substr(&&time,10,2),'07',1,0)),'99') "07",
to_char(sum(decode(substr(&&time,10,2),'08',1,0)),'99') "08",
to_char(sum(decode(substr(&&time,10,2),'09',1,0)),'99') "09",
to_char(sum(decode(substr(&&time,10,2),'10',1,0)),'99') "10",
to_char(sum(decode(substr(&&time,10,2),'11',1,0)),'99') "11",
to_char(sum(decode(substr(&&time,10,2),'12',1,0)),'99') "12",
to_char(sum(decode(substr(&&time,10,2),'13',1,0)),'99') "13",
to_char(sum(decode(substr(&&time,10,2),'14',1,0)),'99') "14",
to_char(sum(decode(substr(&&time,10,2),'15',1,0)),'99') "15",
to_char(sum(decode(substr(&&time,10,2),'16',1,0)),'99') "16",
to_char(sum(decode(substr(&&time,10,2),'17',1,0)),'99') "17",
to_char(sum(decode(substr(&&time,10,2),'18',1,0)),'99') "18",
to_char(sum(decode(substr(&&time,10,2),'19',1,0)),'99') "19",
to_char(sum(decode(substr(&&time,10,2),'20',1,0)),'99') "20",
to_char(sum(decode(substr(&&time,10,2),'21',1,0)),'99') "21",
to_char(sum(decode(substr(&&time,10,2),'22',1,0)),'99') "22",
to_char(sum(decode(substr(&&time,10,2),'23',1,0)),'99') "23"
from sys.v_$log_history
group by substr(&&time,1,5)
/
set colsep " "
12. Compare indexes on two databases and list the differences
col table_name format a30
col column_name format a30
col column_position format 990
accept DB1 prompt "Enter database name to compare from: "
accept DB2 prompt "Enter database name to compare to: "
13. Tables/ columns with indexes on &DB1 that's not on &DB2
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB1.
where table_owner not in ('SYS', 'SYSTEM')
minus
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB2.
where table_owner not in ('SYS', 'SYSTEM')
/
14. Tables/ columns with indexes on &DB2 that's not on &DB1
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB2.
where table_owner not in ('SYS', 'SYSTEM')
minus
select table_owner||'.'||table_name table_name, column_position, column_name
from dba_ind_columns@&DB1.
where table_owner not in ('SYS', 'SYSTEM')
/
spool off
Monday, November 12, 2007
ORACLE 50 FAQS
51. What are the responsibilities of a Database Administrator ?
Installing and upgrading the Oracle Server and application tools.
Allocating system storage and planning future storage requirements for the database system.
Managing primary database structures (tablespaces)
Managing primary objects (table,views,indexes)
Enrolling users and maintaining system security.
Ensuring compliance with Oralce license agreement
Controlling and monitoring user access to the database.
Monitoring and optimising the performance of the database.
Planning for backup and recovery of database information.
Maintain archived data on tape
Backing up and restoring the database.
Contacting Oracle Corporation for technical support.
52. What are the roles and user accounts created automatically with the database ?
DBA - role Contains all database system privileges.
SYS user account - The DBA role will be assigned to this account. All of the basetables and views for the database's dictionary are store in this schema and are manipulated only by ORACLE.
SYSTEM user account - It has all the system privileges for the database and additional tables and views that display administrative information and internal tables and views used by oracle tools are created using this username.
54. What are the database administrators utilities avaliable ?
SQL * DBA - This allows DBA to monitor and control an ORACLE database.
SQL * Loader - It loads data from standard operating system files (Flat files) into ORACLE database tables.
Export (EXP) and Import (imp) utilities allow you to move existing data in ORACLE format to and from ORACLE database.
55. What are the minimum parameters should exist in the parameter file (init.ora) ?
DB NAME - Must set to a text string of no more than 8 characters and it will be stored inside the datafiles, redo log files and control files and control file while database creation.
DB_DOMAIN - It is string that specifies the network domain where the database is created. The global database name is identified by setting these parameters (DB_NAME & DB_DOMAIN)
CONTORL FILES - List of control filenames of the database. If name is not mentioned then default name will be used.
DB_BLOCK_BUFFERS - To determine the no of buffers in the buffer cache in SGA.
PROCESSES - To determine number of operating system processes that can be connected to ORACLE concurrently. The value should be 5 (background process) and additional 1 for each user.
ROLLBACK_SEGMENTS - List of rollback segments an ORACLE instance acquires at database startup.
Also optionally LICENSE_MAX_SESSIONS,LICENSE_SESSION_WARNING and LICENSE_MAX_USERS.
56. What is a trace file and how is it created ?
Each server and background process can write an associated trace file. When an internal error is detected by a process or user process, it dumps information about the error to its trace. This can be used for tuning the database.
57. What are roles ? How can we implement roles ?
Roles are the easiest way to grant and manage common privileges needed by different groups of database users.
Creating roles and assigning provies to roles.
Assign each role to group of users. This will simplify the job of assigning privileges to individual users.
58. What are the steps to switch a database's archiving mode between NO ARCHIVELOG and ARCHIVELOG mode ?
1. Shutdown the database instance.
2. Backup the databse
3. Perform any operating system specific steps (optional)
4. Start up a new instance and mount but do not open the databse.
5. Switch the databse's archiving mode.
59. How can you enable automatic archiving ?
Shut the database
Backup the database
Modify/Include LOG_ARCHIVE_START_TRUE in init.ora file.
Start up the databse.
60. How can we specify the Archived log file name format and destination ?
By setting the following values in init.ora file.
LOG_ARCHIVE_FORMAT = arch %S/s/T/tarc (%S - Log sequence number and is zero left paded, %s - Log sequence number not padded. %T - Thread number lef-zero-paded and %t - Thread number not padded). The file name created is arch 0001 are if %S is used.
LOG_ARCHIVE_DEST = path.
61. What is the use of ANALYZE command ?
To perform one of these function on an index,table, or cluster:
- to collect statisties about object used by the optimizer and store them in the data dictionary.
- to delete statistics about the object used by object from the data dictionary.
- to validate the structure of the object.
- to identify migrated and chained rows of the table or cluster.
MANAGING DISTRIBUTED DATABASES.
62. How can we reduce the network traffic ?
- Replictaion of data in distributed environment.
- Using snapshots to replicate data.
- Using remote procedure calls.
63. What is snapshots ?
Snapshot is an object used to dynamically replicate data between distribute database at specified time intervals. In ver 7.0 they are read only.
64. What are the various type of snapshots ?
Simple and Complex.
65. Differentiate simple and complex, snapshots ?
- A simple snapshot is based on a query that does not contains GROUP BY clauses, CONNECT BY clauses, JOINs, sub-query or snashot of operations.
- A complex snapshots contain atleast any one of the above.
66. What dynamic data replication ?
Updating or Inserting records in remote database through database triggers. It may fail if remote database is having any problem.
67. How can you Enforce Refrencial Integrity in snapshots ?
Time the references to occur when master tables are not in use.
Peform the reference the manually immdiately locking the master tables. We can join tables in snopshots by creating a complex snapshots that will based on the master tables.
68. What are the options available to refresh snapshots ?
COMPLETE - Tables are completly regenerated using the snapshot's query and the master tables every time the snapshot referenced.
FAST - If simple snapshot used then a snapshot log can be used to send the changes to the snapshot tables.
FORCE - Default value. If possible it performs a FAST refresh; Otherwise it will perform a complete refresh.
69. what is snapshot log ?
It is a table that maintains a record of modifications to the master table in a snapshot. It is stored in the same database as master table and is only available for simple snapshots. It should be created before creating snapshots.
70. When will the data in the snapshot log be used ?
We must be able to create a after row trigger on table (i.e., it should be not be already available )
After giving table privileges.
We cannot specify snapshot log name because oracle uses the name of the master table in the name of the database objects that support its snapshot log.
The master table name should be less than or equal to 23 characters.
(The table name created will be MLOGS_tablename, and trigger name will be TLOGS name).
72. What are the benefits of distributed options in databases ?
Database on other servers can be updated and those transactions can be grouped together with others in a logical unit.
Database uses a two phase commit.
MANAGING BACKUP & RECOVERY
73. What are the different methods of backing up oracle database ?
- Logical Backups
- Cold Backups
- Hot Backups (Archive log)
74. What is a logical backup ?
Logical backup involves reading a set of databse records and writing them into a file. Export utility is used for taking backup and Import utility is used to recover from backup.
75. What is cold backup ? What are the elements of it ?
Cold backup is taking backup of all physical files after normal shutdown of database. We need to take.
- All Data files.
- All Control files.
- All on-line redo log files.
30 The init.ora file (Optional)
76. What are the different kind of export backups ?
Full back - Complete database
Incremental - Only affected tables from last incremental date/full backup date.
Cumulative backup - Only affected table from the last cumulative date/full backup date.
77. What is hot backup and how it can be taken ?
Taking backup of archive log files when database is open. For this the ARCHIVELOG mode should be enabled. The following files need to be backed up.
All data files. All Archive log, redo log files. All control files.
78. What is the use of FILE option in EXP command ?
To give the export file name.
79. What is the use of COMPRESS option in EXP command ?
Flag to indicate whether export should compress fragmented segments into single extents.
80. What is the use of GRANT option in EXP command ?
A flag to indicate whether grants on databse objects will be exported or not. Value is 'Y' or 'N'.
81. What is the use of INDEXES option in EXP command ?
A flag to indicate whether indexes on tables will be exported.
82. What is the use of ROWS option in EXP command ?
Flag to indicate whether table rows should be exported. If 'N' only DDL statements for the databse objects will be created.
83. What is the use of CONSTRAINTS option in EXP command ?
A flag to indicate whether constraints on table need to be exported.
84. What is the use of FULL option in EXP command ?
A flag to indicate whether full databse export should be performed.
85. What is the use of OWNER option in EXP command ?
List of table accounts should be exported.
86. What is the use of TABLES option in EXP command ?
List of tables should be exported.
87. What is the use of RECORD LENGTH option in EXP command ?
Record length in bytes.
88. What is the use of INCTYPE option in EXP command ?
Type export should be performed COMPLETE,CUMULATIVE,INCREMENTAL.
89. What is the use of RECORD option in EXP command ?
For Incremental exports, the flag indirects whether a record will be stores data dictionary tables recording the export.
90. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
91. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
92. What is the use of ANALYSE ( Ver 7) option in EXP command ?
A flag to indicate whether statistical information about the exported objects should be written to export dump file.
93. What is the use of CONSISTENT (Ver 7) option in EXP command ?
A flag to indicate whether a read consistent version of all the exported objects should be maintained.
94. What is use of LOG (Ver 7) option in EXP command ?
The name of the file which log of the export will be written.
95.What is the use of FILE option in IMP command ?
The name of the file from which import should be performed.
96. What is the use of SHOW option in IMP command ?
A flag to indicate whether file content should be displayed or not.
97. What is the use of IGNORE option in IMP command ?
A flag to indicate whether the import should ignore errors encounter when issuing CREATE commands.
98. What is the use of GRANT option in IMP command ?
A flag to indicate whether grants on database objects will be imported.
99. What is the use of INDEXES option in IMP command ?
A flag to indicate whether import should import index on tables or not.
100. What is the use of ROWS option in IMP command ?
A flag to indicate whether rows should be imported. If this is set to 'N' then only DDL for database objects will be exectued.
Installing and upgrading the Oracle Server and application tools.
Allocating system storage and planning future storage requirements for the database system.
Managing primary database structures (tablespaces)
Managing primary objects (table,views,indexes)
Enrolling users and maintaining system security.
Ensuring compliance with Oralce license agreement
Controlling and monitoring user access to the database.
Monitoring and optimising the performance of the database.
Planning for backup and recovery of database information.
Maintain archived data on tape
Backing up and restoring the database.
Contacting Oracle Corporation for technical support.
52. What are the roles and user accounts created automatically with the database ?
DBA - role Contains all database system privileges.
SYS user account - The DBA role will be assigned to this account. All of the basetables and views for the database's dictionary are store in this schema and are manipulated only by ORACLE.
SYSTEM user account - It has all the system privileges for the database and additional tables and views that display administrative information and internal tables and views used by oracle tools are created using this username.
54. What are the database administrators utilities avaliable ?
SQL * DBA - This allows DBA to monitor and control an ORACLE database.
SQL * Loader - It loads data from standard operating system files (Flat files) into ORACLE database tables.
Export (EXP) and Import (imp) utilities allow you to move existing data in ORACLE format to and from ORACLE database.
55. What are the minimum parameters should exist in the parameter file (init.ora) ?
DB NAME - Must set to a text string of no more than 8 characters and it will be stored inside the datafiles, redo log files and control files and control file while database creation.
DB_DOMAIN - It is string that specifies the network domain where the database is created. The global database name is identified by setting these parameters (DB_NAME & DB_DOMAIN)
CONTORL FILES - List of control filenames of the database. If name is not mentioned then default name will be used.
DB_BLOCK_BUFFERS - To determine the no of buffers in the buffer cache in SGA.
PROCESSES - To determine number of operating system processes that can be connected to ORACLE concurrently. The value should be 5 (background process) and additional 1 for each user.
ROLLBACK_SEGMENTS - List of rollback segments an ORACLE instance acquires at database startup.
Also optionally LICENSE_MAX_SESSIONS,LICENSE_SESSION_WARNING and LICENSE_MAX_USERS.
56. What is a trace file and how is it created ?
Each server and background process can write an associated trace file. When an internal error is detected by a process or user process, it dumps information about the error to its trace. This can be used for tuning the database.
57. What are roles ? How can we implement roles ?
Roles are the easiest way to grant and manage common privileges needed by different groups of database users.
Creating roles and assigning provies to roles.
Assign each role to group of users. This will simplify the job of assigning privileges to individual users.
58. What are the steps to switch a database's archiving mode between NO ARCHIVELOG and ARCHIVELOG mode ?
1. Shutdown the database instance.
2. Backup the databse
3. Perform any operating system specific steps (optional)
4. Start up a new instance and mount but do not open the databse.
5. Switch the databse's archiving mode.
59. How can you enable automatic archiving ?
Shut the database
Backup the database
Modify/Include LOG_ARCHIVE_START_TRUE in init.ora file.
Start up the databse.
60. How can we specify the Archived log file name format and destination ?
By setting the following values in init.ora file.
LOG_ARCHIVE_FORMAT = arch %S/s/T/tarc (%S - Log sequence number and is zero left paded, %s - Log sequence number not padded. %T - Thread number lef-zero-paded and %t - Thread number not padded). The file name created is arch 0001 are if %S is used.
LOG_ARCHIVE_DEST = path.
61. What is the use of ANALYZE command ?
To perform one of these function on an index,table, or cluster:
- to collect statisties about object used by the optimizer and store them in the data dictionary.
- to delete statistics about the object used by object from the data dictionary.
- to validate the structure of the object.
- to identify migrated and chained rows of the table or cluster.
MANAGING DISTRIBUTED DATABASES.
62. How can we reduce the network traffic ?
- Replictaion of data in distributed environment.
- Using snapshots to replicate data.
- Using remote procedure calls.
63. What is snapshots ?
Snapshot is an object used to dynamically replicate data between distribute database at specified time intervals. In ver 7.0 they are read only.
64. What are the various type of snapshots ?
Simple and Complex.
65. Differentiate simple and complex, snapshots ?
- A simple snapshot is based on a query that does not contains GROUP BY clauses, CONNECT BY clauses, JOINs, sub-query or snashot of operations.
- A complex snapshots contain atleast any one of the above.
66. What dynamic data replication ?
Updating or Inserting records in remote database through database triggers. It may fail if remote database is having any problem.
67. How can you Enforce Refrencial Integrity in snapshots ?
Time the references to occur when master tables are not in use.
Peform the reference the manually immdiately locking the master tables. We can join tables in snopshots by creating a complex snapshots that will based on the master tables.
68. What are the options available to refresh snapshots ?
COMPLETE - Tables are completly regenerated using the snapshot's query and the master tables every time the snapshot referenced.
FAST - If simple snapshot used then a snapshot log can be used to send the changes to the snapshot tables.
FORCE - Default value. If possible it performs a FAST refresh; Otherwise it will perform a complete refresh.
69. what is snapshot log ?
It is a table that maintains a record of modifications to the master table in a snapshot. It is stored in the same database as master table and is only available for simple snapshots. It should be created before creating snapshots.
70. When will the data in the snapshot log be used ?
We must be able to create a after row trigger on table (i.e., it should be not be already available )
After giving table privileges.
We cannot specify snapshot log name because oracle uses the name of the master table in the name of the database objects that support its snapshot log.
The master table name should be less than or equal to 23 characters.
(The table name created will be MLOGS_tablename, and trigger name will be TLOGS name).
72. What are the benefits of distributed options in databases ?
Database on other servers can be updated and those transactions can be grouped together with others in a logical unit.
Database uses a two phase commit.
MANAGING BACKUP & RECOVERY
73. What are the different methods of backing up oracle database ?
- Logical Backups
- Cold Backups
- Hot Backups (Archive log)
74. What is a logical backup ?
Logical backup involves reading a set of databse records and writing them into a file. Export utility is used for taking backup and Import utility is used to recover from backup.
75. What is cold backup ? What are the elements of it ?
Cold backup is taking backup of all physical files after normal shutdown of database. We need to take.
- All Data files.
- All Control files.
- All on-line redo log files.
30 The init.ora file (Optional)
76. What are the different kind of export backups ?
Full back - Complete database
Incremental - Only affected tables from last incremental date/full backup date.
Cumulative backup - Only affected table from the last cumulative date/full backup date.
77. What is hot backup and how it can be taken ?
Taking backup of archive log files when database is open. For this the ARCHIVELOG mode should be enabled. The following files need to be backed up.
All data files. All Archive log, redo log files. All control files.
78. What is the use of FILE option in EXP command ?
To give the export file name.
79. What is the use of COMPRESS option in EXP command ?
Flag to indicate whether export should compress fragmented segments into single extents.
80. What is the use of GRANT option in EXP command ?
A flag to indicate whether grants on databse objects will be exported or not. Value is 'Y' or 'N'.
81. What is the use of INDEXES option in EXP command ?
A flag to indicate whether indexes on tables will be exported.
82. What is the use of ROWS option in EXP command ?
Flag to indicate whether table rows should be exported. If 'N' only DDL statements for the databse objects will be created.
83. What is the use of CONSTRAINTS option in EXP command ?
A flag to indicate whether constraints on table need to be exported.
84. What is the use of FULL option in EXP command ?
A flag to indicate whether full databse export should be performed.
85. What is the use of OWNER option in EXP command ?
List of table accounts should be exported.
86. What is the use of TABLES option in EXP command ?
List of tables should be exported.
87. What is the use of RECORD LENGTH option in EXP command ?
Record length in bytes.
88. What is the use of INCTYPE option in EXP command ?
Type export should be performed COMPLETE,CUMULATIVE,INCREMENTAL.
89. What is the use of RECORD option in EXP command ?
For Incremental exports, the flag indirects whether a record will be stores data dictionary tables recording the export.
90. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
91. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
92. What is the use of ANALYSE ( Ver 7) option in EXP command ?
A flag to indicate whether statistical information about the exported objects should be written to export dump file.
93. What is the use of CONSISTENT (Ver 7) option in EXP command ?
A flag to indicate whether a read consistent version of all the exported objects should be maintained.
94. What is use of LOG (Ver 7) option in EXP command ?
The name of the file which log of the export will be written.
95.What is the use of FILE option in IMP command ?
The name of the file from which import should be performed.
96. What is the use of SHOW option in IMP command ?
A flag to indicate whether file content should be displayed or not.
97. What is the use of IGNORE option in IMP command ?
A flag to indicate whether the import should ignore errors encounter when issuing CREATE commands.
98. What is the use of GRANT option in IMP command ?
A flag to indicate whether grants on database objects will be imported.
99. What is the use of INDEXES option in IMP command ?
A flag to indicate whether import should import index on tables or not.
100. What is the use of ROWS option in IMP command ?
A flag to indicate whether rows should be imported. If this is set to 'N' then only DDL for database objects will be exectued.
ORACLE FAQS
1. What is a Database instance ? Explain
A database instance (Server) is a set of memory structure and background processes that access a set of database files.
The process can be shared by all users.
The memory structure that are used to store most queried data from database. This helps up to improve database performance by decreasing the amount of I/O performed against data file.
2. What is Parallel Server ?
Multiple instances accessing the same database (Only In Multi-CPU environments)
3. What is a Schema ?
The set of objects owned by user account is called the schema.
4. What is an Index ? How it is implemented in Oracle Database ?
An index is a database structure used by the server to have direct access of a row in a table.
An index is automatically created when a unique of primary key constraint clause is specified in create table comman (Ver 7.0)
5. What is clusters ?
Group of tables physically stored together because they share common columns and are often used together is called Cluster.
6. What is a cluster Key ?
The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stored only once for multiple tables in the cluster.
7. What are the basic element of Base configuration of an oracle Database ?
It consists of
one or more data files.
one or more control files.
two or more redo log files.
The Database contains
multiple users/schemas
one or more rollback segments
one or more tablespaces
Data dictionary tables
User objects (table,indexes,views etc.,)
The server that access the database consists of
SGA (Database buffer, Dictionary Cache Buffers, Redo log buffers, Shared SQL pool)
SMON (System MONito)
PMON (Process MONitor)
LGWR (LoG Write)
DBWR (Data Base Write)
ARCH (ARCHiver)
CKPT (Check Point)
RECO
Dispatcher
User Process with associated PGS
8. What is a deadlock ? Explain .
Two processes wating to update the rows of a table which are locked by the other process then deadlock arises.
In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically.
These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.
MEMORY MANAGEMENT
9. What is SGA ? How it is different from Ver 6.0 and Ver 7.0 ?
The System Global Area in a Oracle database is the area in memory to facilitates the transfer of information between users. It holds the most recently requested structural information between users. It holds the most recently requested structural information about the database.
The structure is Database buffers, Dictionary cache, Redo Log Buffer and Shared SQL pool (ver 7.0 only) area.
10. What is a Shared SQL pool ?
The data dictionary cache is stored in an area in SGA called the Shared SQL Pool. This will allow sharing of parsed SQL statements among concurrent users.
11. What is mean by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User Process.
12. What is a data segment ?
Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored.
13. What are the factors causing the reparsing of SQL statements in SGA?
Due to insufficient Shared SQL pool size.
Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater than 1 then increase the SHARED_POOL_SIZE.
LOGICAL & PHYSICAL ARCHITECTURE OF DATABASE.
14. What is Database Buffers ?
Database buffers are cache in the SGA used to hold the data blocks that are read from the data segments in the database such as tables, indexes and clusters DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size.
15. What is dictionary cache ?
Dictionary cache is information about the databse objects stored in a data dictionary table.
16. What is meant by recursive hints ?
Number of times processes repeatedly query the dictionary table is called recursive hints. It is due to the data dictionary cache is too small. By increasing the SHARED_POOL_SIZE parameter we can optimize the size of Data Dictionary Cache.
17. What is meant by redo log buffer ?
Change made to entries are written to the on-line redo log files. So that they can be used in roll forward operations during database recoveries. Before writing them into the redo log files, they will first brought to redo log buffers in SGA and LGWR will write into files frequently.
LOG_BUFFER parameter will decide the size.
18. How will you swap objects into a different table space for an existing database ?
Export the user
Perform import using the command imp system/manager file=export.dmp indexfile=newrite.sql. This will create all definitions into newfile.sql.
Drop necessary objects.
Run the script newfile.sql after altering the tablespaces.
Import from the backup for the necessary objects.
19. List the Optional Flexible Architecture (OFA) of Oracle database ? or How can we organise the tablespaces in Oracle database to have maximum performance ?
SYSTEM - Data dictionary tables.
DATA - Standard operational tables.
DATA2- Static tables used for standard operations
INDEXES - Indexes for Standard operational tables.
INDEXES1 - Indexes of static tables used for standard operations.
TOOLS - Tools table.
TOOLS1 - Indexes for tools table.
RBS - Standard Operations Rollback Segments,
RBS1,RBS2 - Additional/Special Rollback segments.
TEMP - Temporary purpose tablespace
TEMP_USER - Temporary tablespace for users.
USERS - User tablespace.
20. How will you force database to use particular rollback segment ?
SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.
21. What is meant by free extent ?
A free extent is a collection of continuous free blocks in tablespace. When a segment is dropped its extents are reallocated and are marked as free.
22. How free extents are managed in Ver 6.0 and Ver 7.0 ?
Free extents cannot be merged together in Ver 6.0.
Free extents are periodically coalesces with the neighboring free extent in
Ver 7.0
23.Which parameter in Storage clause will reduce no. of rows per block?
PCTFREE parameter
Row size also reduces no of rows per block.
24. What is the significance of having storage clause ?
We can plan the storage for a table as how much initial extents are required, how much can be extended next, how much % should leave free for managing row updations etc.,
25. How does Space allocation table place within a block ?
Each block contains entries as follows
Fixied block header
Variable block header
Row Header,row date (multiple rows may exists)
PCTEREE (% of free space for row updation in future)
26. What is the role of PCTFREE parameter is Storage clause ?
This is used to reserve certain amount of space in a block for expansion of rows.
27. What is the OPTIMAL parameter ?
It is used to set the optimal length of a rollback segment.
28. What is the functionality of SYSTEM table space ?
To manage the database level transactions such as modifications of the data dictionary table that record information about the free space usage.
29. How will you create multiple rollback segments in a database ?
Create a database which implicitly creates a SYSTEM Rollback Segment in a SYSTEM tablespace.
Create a Second Rollback Segment name R0 in the SYSTEM tablespace.
Make new rollback segment available (After shutdown, modify init.ora file and Start database)
Create other tablespaces (RBS) for rollback segments.
Deactivate Rollback Segment R0 and activate the newly created rollback segments.
30. How the space utilisation takes place within rollback segments ?
It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an extent is in use then it forced to acquire a new extent (No. of extents is based on the optimal size)
31. Why query fails sometimes ?
Rollback segment dynamically extent to handle larger transactions entry loads.
A single transaction may wipeout all avaliable free space in the Rollback Segment Tablespace. This prevents other user using Rollback segments.
32. How will you monitor the space allocation ?
By quering DBA_SEGMENT table/view.
33. How will you monitor rollback segment status ?
Querying the DBA_ROLLBACK_SEGS view
IN USE - Rollback Segment is on-line.
AVAILABLE - Rollback Segment available but not on-line.
OFF-LINE - Rollback Segment off-line
INVALID - Rollback Segment Dropped.
NEEDS RECOVERY - Contains data but need recovery or corupted.
PARTLY AVAILABLE - Contains data from an unresolved transaction involving a distributed database.
34. List the sequence of events when a large transaction that exceeds beyond its optimal value when an entry wraps and causes the rollback segment to expand into another extend.
Transaction Begins.
An entry is made in the RES header for new transactions entry
Transaction acquires blocks in an extent of RBS
The entry attempts to wrap into second extent. None is available, so that the RBS must extent.
The RBS checks to see if it is part of its OPTIMAL size.
RBS chooses its oldest inactive segment.
Oldest inactive segment is eliminated.
RBS extents
The Data dictionary table for space management are updated.
Transaction Completes.
35. How can we plan storage for very large tables ?
Limit the number of extents in the table
Separate Table from its indexes.
Allocate Sufficient temporary storage.
36. How will you estimate the space required by a non-clustered tables?
Calculate the total header size
Calculate the available dataspace per data block
Calculate the combined column lengths of the average row
Calculate the total average row size.
Calculate the average number rows that can fit in a block
Calculate the number of blocks and bytes required for the table.
After arriving the calculation, add 10 % additional space to calculate the initial extent size for a working table.
37. It is possible to use raw devices as data files and what is the advantages over file. system files ?
Yes.
The advantages over file system files.
I/O will be improved because Oracle is bye-passing the kernnel which writing into disk.
Disk Corruption will be very less.
38. What is a Control file ?
Database's overall physical architecture is maintained in a file called control file. It will be used to maintain internal consistency and guide recovery operations. Multiple copies of control files are advisable.
39. How to implement the multiple control files for an existing database ?
Shutdown the databse
Copy one of the existing control file to new location
Edit Config ora file by adding new control file.name
Restart the database.
40. What is meant by Redo Log file mirrorring ? How it can be achieved?
Process of having a copy of redo log files is called mirroring.
This can be achieved by creating group of log files together, so that LGWR will automatically writes them to all the members of the current on-line redo log group. If any one group fails then database automatically switch over to next group. It degrades performance.
41. What is advantage of having disk shadowing/ Mirroring ?
Shadow set of disks save as a backup in the event of disk failure. In most Operating System if any disk failure occurs it automatically switchover to place of failed disk.
Improved performance because most OS support volume shadowing can direct file I/O request to use the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks.
42. What is use of Rollback Segments In Database ?
They allow the database to maintain read consistency between multiple transactions.
43. What is a Rollback segment entry ?
It is the set of before image data blocks that contain rows that are modified by a transaction.
Each Rollback Segment entry must be completed within one rollback segment.
A single rollback segment can have multiple rollback segment entries.
44. What is hit ratio ?
It is a measure of well the data cache buffer is handling requests for data.
Hit Ratio = (Logical Reads - Physical Reads - Hits Misses)/ Logical Reads.
45. When will be a segment released ?
When Segment is dropped.
When Shrink (RBS only)
When truncated (TRUNCATE used with drop storage option)
46. What are disadvanteges of having raw devices ?
We should depend on export/import utility for backup/recovery (fully reliable)
The tar command cannot be used for physical file backup, instead we can use dd command which is less flexible and has limited recoveries.
47. List the factors that can affect the accuracy of the estimations ?
The space used transaction entries and deleted records does not become free immediately after completion due to delayed cleanout.
Trailling nulls and length bytes are not stored.
Inserts of, updates to and deletes of rows as well as columns larger than a single datablock, can cause fragmentation an chained row pieces.
DATABASE SECURITY & ADMINISTRATION
48. What is user Account in Oracle database ?
An user account is not a physical structure in Database but it is having important relationship to the objects in the database and will be having certain privileges.
49. How will you enforce security using stored procedures ?
Don't grant user access directly to tables within the application.
Instead grant the ability to access the procedures that access the tables.
When procedure executed it will execute the privilege of procedures owner. Users cannot access tables except via the procedure.
50. What are the dictionary tables used to monitor a database spaces ?
DBA_FREE_SPACE
DBA_SEGMENTS
DBA_DATA_FILES.
A database instance (Server) is a set of memory structure and background processes that access a set of database files.
The process can be shared by all users.
The memory structure that are used to store most queried data from database. This helps up to improve database performance by decreasing the amount of I/O performed against data file.
2. What is Parallel Server ?
Multiple instances accessing the same database (Only In Multi-CPU environments)
3. What is a Schema ?
The set of objects owned by user account is called the schema.
4. What is an Index ? How it is implemented in Oracle Database ?
An index is a database structure used by the server to have direct access of a row in a table.
An index is automatically created when a unique of primary key constraint clause is specified in create table comman (Ver 7.0)
5. What is clusters ?
Group of tables physically stored together because they share common columns and are often used together is called Cluster.
6. What is a cluster Key ?
The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stored only once for multiple tables in the cluster.
7. What are the basic element of Base configuration of an oracle Database ?
It consists of
one or more data files.
one or more control files.
two or more redo log files.
The Database contains
multiple users/schemas
one or more rollback segments
one or more tablespaces
Data dictionary tables
User objects (table,indexes,views etc.,)
The server that access the database consists of
SGA (Database buffer, Dictionary Cache Buffers, Redo log buffers, Shared SQL pool)
SMON (System MONito)
PMON (Process MONitor)
LGWR (LoG Write)
DBWR (Data Base Write)
ARCH (ARCHiver)
CKPT (Check Point)
RECO
Dispatcher
User Process with associated PGS
8. What is a deadlock ? Explain .
Two processes wating to update the rows of a table which are locked by the other process then deadlock arises.
In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically.
These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.
MEMORY MANAGEMENT
9. What is SGA ? How it is different from Ver 6.0 and Ver 7.0 ?
The System Global Area in a Oracle database is the area in memory to facilitates the transfer of information between users. It holds the most recently requested structural information between users. It holds the most recently requested structural information about the database.
The structure is Database buffers, Dictionary cache, Redo Log Buffer and Shared SQL pool (ver 7.0 only) area.
10. What is a Shared SQL pool ?
The data dictionary cache is stored in an area in SGA called the Shared SQL Pool. This will allow sharing of parsed SQL statements among concurrent users.
11. What is mean by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User Process.
12. What is a data segment ?
Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored.
13. What are the factors causing the reparsing of SQL statements in SGA?
Due to insufficient Shared SQL pool size.
Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater than 1 then increase the SHARED_POOL_SIZE.
LOGICAL & PHYSICAL ARCHITECTURE OF DATABASE.
14. What is Database Buffers ?
Database buffers are cache in the SGA used to hold the data blocks that are read from the data segments in the database such as tables, indexes and clusters DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size.
15. What is dictionary cache ?
Dictionary cache is information about the databse objects stored in a data dictionary table.
16. What is meant by recursive hints ?
Number of times processes repeatedly query the dictionary table is called recursive hints. It is due to the data dictionary cache is too small. By increasing the SHARED_POOL_SIZE parameter we can optimize the size of Data Dictionary Cache.
17. What is meant by redo log buffer ?
Change made to entries are written to the on-line redo log files. So that they can be used in roll forward operations during database recoveries. Before writing them into the redo log files, they will first brought to redo log buffers in SGA and LGWR will write into files frequently.
LOG_BUFFER parameter will decide the size.
18. How will you swap objects into a different table space for an existing database ?
Export the user
Perform import using the command imp system/manager file=export.dmp indexfile=newrite.sql. This will create all definitions into newfile.sql.
Drop necessary objects.
Run the script newfile.sql after altering the tablespaces.
Import from the backup for the necessary objects.
19. List the Optional Flexible Architecture (OFA) of Oracle database ? or How can we organise the tablespaces in Oracle database to have maximum performance ?
SYSTEM - Data dictionary tables.
DATA - Standard operational tables.
DATA2- Static tables used for standard operations
INDEXES - Indexes for Standard operational tables.
INDEXES1 - Indexes of static tables used for standard operations.
TOOLS - Tools table.
TOOLS1 - Indexes for tools table.
RBS - Standard Operations Rollback Segments,
RBS1,RBS2 - Additional/Special Rollback segments.
TEMP - Temporary purpose tablespace
TEMP_USER - Temporary tablespace for users.
USERS - User tablespace.
20. How will you force database to use particular rollback segment ?
SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.
21. What is meant by free extent ?
A free extent is a collection of continuous free blocks in tablespace. When a segment is dropped its extents are reallocated and are marked as free.
22. How free extents are managed in Ver 6.0 and Ver 7.0 ?
Free extents cannot be merged together in Ver 6.0.
Free extents are periodically coalesces with the neighboring free extent in
Ver 7.0
23.Which parameter in Storage clause will reduce no. of rows per block?
PCTFREE parameter
Row size also reduces no of rows per block.
24. What is the significance of having storage clause ?
We can plan the storage for a table as how much initial extents are required, how much can be extended next, how much % should leave free for managing row updations etc.,
25. How does Space allocation table place within a block ?
Each block contains entries as follows
Fixied block header
Variable block header
Row Header,row date (multiple rows may exists)
PCTEREE (% of free space for row updation in future)
26. What is the role of PCTFREE parameter is Storage clause ?
This is used to reserve certain amount of space in a block for expansion of rows.
27. What is the OPTIMAL parameter ?
It is used to set the optimal length of a rollback segment.
28. What is the functionality of SYSTEM table space ?
To manage the database level transactions such as modifications of the data dictionary table that record information about the free space usage.
29. How will you create multiple rollback segments in a database ?
Create a database which implicitly creates a SYSTEM Rollback Segment in a SYSTEM tablespace.
Create a Second Rollback Segment name R0 in the SYSTEM tablespace.
Make new rollback segment available (After shutdown, modify init.ora file and Start database)
Create other tablespaces (RBS) for rollback segments.
Deactivate Rollback Segment R0 and activate the newly created rollback segments.
30. How the space utilisation takes place within rollback segments ?
It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an extent is in use then it forced to acquire a new extent (No. of extents is based on the optimal size)
31. Why query fails sometimes ?
Rollback segment dynamically extent to handle larger transactions entry loads.
A single transaction may wipeout all avaliable free space in the Rollback Segment Tablespace. This prevents other user using Rollback segments.
32. How will you monitor the space allocation ?
By quering DBA_SEGMENT table/view.
33. How will you monitor rollback segment status ?
Querying the DBA_ROLLBACK_SEGS view
IN USE - Rollback Segment is on-line.
AVAILABLE - Rollback Segment available but not on-line.
OFF-LINE - Rollback Segment off-line
INVALID - Rollback Segment Dropped.
NEEDS RECOVERY - Contains data but need recovery or corupted.
PARTLY AVAILABLE - Contains data from an unresolved transaction involving a distributed database.
34. List the sequence of events when a large transaction that exceeds beyond its optimal value when an entry wraps and causes the rollback segment to expand into another extend.
Transaction Begins.
An entry is made in the RES header for new transactions entry
Transaction acquires blocks in an extent of RBS
The entry attempts to wrap into second extent. None is available, so that the RBS must extent.
The RBS checks to see if it is part of its OPTIMAL size.
RBS chooses its oldest inactive segment.
Oldest inactive segment is eliminated.
RBS extents
The Data dictionary table for space management are updated.
Transaction Completes.
35. How can we plan storage for very large tables ?
Limit the number of extents in the table
Separate Table from its indexes.
Allocate Sufficient temporary storage.
36. How will you estimate the space required by a non-clustered tables?
Calculate the total header size
Calculate the available dataspace per data block
Calculate the combined column lengths of the average row
Calculate the total average row size.
Calculate the average number rows that can fit in a block
Calculate the number of blocks and bytes required for the table.
After arriving the calculation, add 10 % additional space to calculate the initial extent size for a working table.
37. It is possible to use raw devices as data files and what is the advantages over file. system files ?
Yes.
The advantages over file system files.
I/O will be improved because Oracle is bye-passing the kernnel which writing into disk.
Disk Corruption will be very less.
38. What is a Control file ?
Database's overall physical architecture is maintained in a file called control file. It will be used to maintain internal consistency and guide recovery operations. Multiple copies of control files are advisable.
39. How to implement the multiple control files for an existing database ?
Shutdown the databse
Copy one of the existing control file to new location
Edit Config ora file by adding new control file.name
Restart the database.
40. What is meant by Redo Log file mirrorring ? How it can be achieved?
Process of having a copy of redo log files is called mirroring.
This can be achieved by creating group of log files together, so that LGWR will automatically writes them to all the members of the current on-line redo log group. If any one group fails then database automatically switch over to next group. It degrades performance.
41. What is advantage of having disk shadowing/ Mirroring ?
Shadow set of disks save as a backup in the event of disk failure. In most Operating System if any disk failure occurs it automatically switchover to place of failed disk.
Improved performance because most OS support volume shadowing can direct file I/O request to use the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks.
42. What is use of Rollback Segments In Database ?
They allow the database to maintain read consistency between multiple transactions.
43. What is a Rollback segment entry ?
It is the set of before image data blocks that contain rows that are modified by a transaction.
Each Rollback Segment entry must be completed within one rollback segment.
A single rollback segment can have multiple rollback segment entries.
44. What is hit ratio ?
It is a measure of well the data cache buffer is handling requests for data.
Hit Ratio = (Logical Reads - Physical Reads - Hits Misses)/ Logical Reads.
45. When will be a segment released ?
When Segment is dropped.
When Shrink (RBS only)
When truncated (TRUNCATE used with drop storage option)
46. What are disadvanteges of having raw devices ?
We should depend on export/import utility for backup/recovery (fully reliable)
The tar command cannot be used for physical file backup, instead we can use dd command which is less flexible and has limited recoveries.
47. List the factors that can affect the accuracy of the estimations ?
The space used transaction entries and deleted records does not become free immediately after completion due to delayed cleanout.
Trailling nulls and length bytes are not stored.
Inserts of, updates to and deletes of rows as well as columns larger than a single datablock, can cause fragmentation an chained row pieces.
DATABASE SECURITY & ADMINISTRATION
48. What is user Account in Oracle database ?
An user account is not a physical structure in Database but it is having important relationship to the objects in the database and will be having certain privileges.
49. How will you enforce security using stored procedures ?
Don't grant user access directly to tables within the application.
Instead grant the ability to access the procedures that access the tables.
When procedure executed it will execute the privilege of procedures owner. Users cannot access tables except via the procedure.
50. What are the dictionary tables used to monitor a database spaces ?
DBA_FREE_SPACE
DBA_SEGMENTS
DBA_DATA_FILES.
Friday, November 2, 2007
recover from deleted transaction log
This document will give instructions on how to recover from a deleted database log file on Microsoft SQL Server. The database this was done on was SQL Server 7 with SQL Server 2000. You will get a suspect beside the name of the database when this happens.
You may be interested in the document if one of the following happened:
You're log file got too big so you decided to shutdown SQL Server,
then delete the log file.
Salvage data from a damaged SQL data (.MDF) file. ( Someone emailed about this ).
That's the only reason I can think of right now and that is the reason I have come to figuring this out, so here goes.
Instructions
If you have a recent backup of the database, USE IT! Forget about this article and do a normal restore procedure. Otherwise read on. First of all, you are SOL if you want a full recovery. You just can'tget all the data back because the log file itself contained a lot of transactions that may never have made it to the data file.
So anyways, I read just about everything possible on this topic and nothing worked, I mean nothing. I tried going into emergency mode, running stored procedures that did squat, using sp_detach_db, then sp_attach_db, etc, even trying db_rebuild_log() (the rebuild_log thing seems to be an undocumented feature that someone must have figured out... easter egg?? not really since there are some serious warnings against using it, but hey, when you're in dire straits, you'll try anything once, right?).
This restore procedure doesn't seem to be formally documented anywhere. I guess you're just not supposed to be this stupid, but everybody makes mistakes don't they? And hey, I'm no DBA or anything! I just use the damn things. ;-)
Anyways, on to the guts of the article. I am trying to make this as simple
as possible and pulling this from memory so if there is something I am
missing, please post a comment.
There's one thing to note here and if someone could verify it, that would be great. First thing I'd like to verify is if you can just skip to step 9 right off the bat? So as soon as you get a suspect database, can you just start at step 9? Can someone please try that and let me know. SEE
UPDATE: JAN. 6, 2003 BELOW
Backup the data (.mdf) file! Just in case. We take no responsibility
for anything that happens following this procedure.
EXEC sp_detach_db 'dbname' -- this will detach the database from
the server
Restart SQL Server
The database may still be seen in enterprise manager, but just ignore
it.
Create a new database with the same name or a different name. You
will have to use a different physical file name, which is fine.
Stop SQL Server.
Rename the new data file that was created to something else (ex: add.bak
to the end)
Rename the old data file that you want to restore to the name of the
newly created file (the same name as the file you changed in the step
above)
Start SQL Server
Now the db will still be suspect but you now have a log file.
Switch to emergency mode on the database. You do this by doing the
following:
Right click on the database root node in Enterprise manager and
bring up the properties.
Under the Server Settings tab, check of "Allow modifications
to be made directly to the system catalogs".
click ok
Now go to the master database and open the sysdatabases
table.
Find the suspected database in here and modify the status column,
setting it to: 32768. This will put it into emergency mode.
stop then start sql server
Now here's the tricky part and I'm not sure how this will work on
a single install, i was lucky enough to have SQL Server 2000 installed.
But anyways, open up the Import and Export Data (DTS) program from the
start menu. And you want to copy data from the old database to a brand
new one. Just copy tables and views.
You may be interested in the document if one of the following happened:
You're log file got too big so you decided to shutdown SQL Server,
then delete the log file.
Salvage data from a damaged SQL data (.MDF) file. ( Someone emailed about this ).
That's the only reason I can think of right now and that is the reason I have come to figuring this out, so here goes.
Instructions
If you have a recent backup of the database, USE IT! Forget about this article and do a normal restore procedure. Otherwise read on. First of all, you are SOL if you want a full recovery. You just can'tget all the data back because the log file itself contained a lot of transactions that may never have made it to the data file.
So anyways, I read just about everything possible on this topic and nothing worked, I mean nothing. I tried going into emergency mode, running stored procedures that did squat, using sp_detach_db, then sp_attach_db, etc, even trying db_rebuild_log() (the rebuild_log thing seems to be an undocumented feature that someone must have figured out... easter egg?? not really since there are some serious warnings against using it, but hey, when you're in dire straits, you'll try anything once, right?).
This restore procedure doesn't seem to be formally documented anywhere. I guess you're just not supposed to be this stupid, but everybody makes mistakes don't they? And hey, I'm no DBA or anything! I just use the damn things. ;-)
Anyways, on to the guts of the article. I am trying to make this as simple
as possible and pulling this from memory so if there is something I am
missing, please post a comment.
There's one thing to note here and if someone could verify it, that would be great. First thing I'd like to verify is if you can just skip to step 9 right off the bat? So as soon as you get a suspect database, can you just start at step 9? Can someone please try that and let me know. SEE
UPDATE: JAN. 6, 2003 BELOW
Backup the data (.mdf) file! Just in case. We take no responsibility
for anything that happens following this procedure.
EXEC sp_detach_db 'dbname' -- this will detach the database from
the server
Restart SQL Server
The database may still be seen in enterprise manager, but just ignore
it.
Create a new database with the same name or a different name. You
will have to use a different physical file name, which is fine.
Stop SQL Server.
Rename the new data file that was created to something else (ex: add.bak
to the end)
Rename the old data file that you want to restore to the name of the
newly created file (the same name as the file you changed in the step
above)
Start SQL Server
Now the db will still be suspect but you now have a log file.
Switch to emergency mode on the database. You do this by doing the
following:
Right click on the database root node in Enterprise manager and
bring up the properties.
Under the Server Settings tab, check of "Allow modifications
to be made directly to the system catalogs".
click ok
Now go to the master database and open the sysdatabases
table.
Find the suspected database in here and modify the status column,
setting it to: 32768. This will put it into emergency mode.
stop then start sql server
Now here's the tricky part and I'm not sure how this will work on
a single install, i was lucky enough to have SQL Server 2000 installed.
But anyways, open up the Import and Export Data (DTS) program from the
start menu. And you want to copy data from the old database to a brand
new one. Just copy tables and views.
To Delete Duplicate Rows
For this example, we will use the following table with duplicate PK values. In this table the primary key is the two columns (col1,
col2). We cannot create a unique index or PRIMARY KEY constraint since two rows have duplicate PKs. This procedure illustrates how to identify and remove the duplicates.
create table t1(col1 int, col2 int, col3 char(50))
insert into t1 values (1, 1, 'data value one')
insert into t1 values (1, 1, 'data value one')
insert into t1 values (1, 2, 'data value two')
The first step is to identify which rows have duplicate primary key values:
SELECT col1, col2, count(*)
FROM t1
GROUP BY col1, col2
HAVING count(*) > 1
This will return one row for each set of duplicate PK values in the table. The last column in this result is the number of duplicates for the particular PK value.
col1 col2
1 1 2
If there are only a few sets of duplicate PK values, the best procedure is to delete these manually on an individual basis. For example:
set rowcount 1
delete from t1
where col1=1 and col2=1
The rowcount value should be n-1 the number of duplicates for a given key value. In this example, there are 2 duplicates so rowcount is set to 1. The col1/col2 values are taken from the above GROUP BY query result. If the GROUP BY query returns multiple rows, the "set rowcount" query will have to be run once for each of these rows. Each time it is run, set rowcount to n-1 the number of duplicates of the particular PK value.
Before deleting the rows, you should verify that the entire row is duplicate. While unlikely, it is possible that the PK values are duplicate, yet the row as a whole is not. An example of this would be a table with Social Security Number as the primary key, and having two different people (or rows) with the same number, each having unique attributes. In such a case whatever malfunction caused the duplicate key may have also caused valid unique data to be placed in the row. This data should copied out and preserved for study and possible reconciliation prior to deleting the data.
If there are many distinct sets of duplicate PK values in the table, it may be too time-consuming to remove them individually. In this case the following procedure can be used: 1. First, run the above GROUP BY query to determine how many sets of duplicate PK values exist, and the count of duplicates for each set.
2. Select the duplicate key values into a holding table. For example:
SELECT col1, col2, col3=count(*)
INTO holdkey
FROM t1
GROUP BY col1, col2
HAVING count(*) > 1
3. Select the duplicate rows into a holding table, eliminating duplicates in the process. For example:
SELECT DISTINCT t1.*
INTO holddups
FROM t1, holdkey
WHERE t1.col1 = holdkey.col1
AND t1.col2 = holdkey.col2
4. At this point, the holddups table should have unique PKs, however, this will not be the case if t1 had duplicate PKs, yet unique rows (as in the SSN example above). Verify that each key in holddups is unique, and that you do not have duplicate keys, yet unique rows. If so, you must stop here and reconcile which of the rows you wish to keep for a given duplicate key value. For example, the query:
SELECT col1, col2, count(*)
FROM holddups
GROUP BY col1, col2
should return a count of 1 for each row. If yes, proceed to step 5 below. If no, you have duplicate keys, yet unique rows, and need to decide which rows to save. This will usually entail either discarding a row, or creating a new unique key value for this row. Take one of these two steps for each such duplicate PK in the holddups table.
5. Delete the duplicate rows from the original table. For example:
DELETE t1
FROM t1, holdkey
WHERE t1.col1 = holdkey.col1
AND t1.col2 = holdkey.col2
6. Put the unique rows back in the original table. For example:
INSERT t1 SELECT * FROM holddups
col2). We cannot create a unique index or PRIMARY KEY constraint since two rows have duplicate PKs. This procedure illustrates how to identify and remove the duplicates.
create table t1(col1 int, col2 int, col3 char(50))
insert into t1 values (1, 1, 'data value one')
insert into t1 values (1, 1, 'data value one')
insert into t1 values (1, 2, 'data value two')
The first step is to identify which rows have duplicate primary key values:
SELECT col1, col2, count(*)
FROM t1
GROUP BY col1, col2
HAVING count(*) > 1
This will return one row for each set of duplicate PK values in the table. The last column in this result is the number of duplicates for the particular PK value.
col1 col2
1 1 2
If there are only a few sets of duplicate PK values, the best procedure is to delete these manually on an individual basis. For example:
set rowcount 1
delete from t1
where col1=1 and col2=1
The rowcount value should be n-1 the number of duplicates for a given key value. In this example, there are 2 duplicates so rowcount is set to 1. The col1/col2 values are taken from the above GROUP BY query result. If the GROUP BY query returns multiple rows, the "set rowcount" query will have to be run once for each of these rows. Each time it is run, set rowcount to n-1 the number of duplicates of the particular PK value.
Before deleting the rows, you should verify that the entire row is duplicate. While unlikely, it is possible that the PK values are duplicate, yet the row as a whole is not. An example of this would be a table with Social Security Number as the primary key, and having two different people (or rows) with the same number, each having unique attributes. In such a case whatever malfunction caused the duplicate key may have also caused valid unique data to be placed in the row. This data should copied out and preserved for study and possible reconciliation prior to deleting the data.
If there are many distinct sets of duplicate PK values in the table, it may be too time-consuming to remove them individually. In this case the following procedure can be used: 1. First, run the above GROUP BY query to determine how many sets of duplicate PK values exist, and the count of duplicates for each set.
2. Select the duplicate key values into a holding table. For example:
SELECT col1, col2, col3=count(*)
INTO holdkey
FROM t1
GROUP BY col1, col2
HAVING count(*) > 1
3. Select the duplicate rows into a holding table, eliminating duplicates in the process. For example:
SELECT DISTINCT t1.*
INTO holddups
FROM t1, holdkey
WHERE t1.col1 = holdkey.col1
AND t1.col2 = holdkey.col2
4. At this point, the holddups table should have unique PKs, however, this will not be the case if t1 had duplicate PKs, yet unique rows (as in the SSN example above). Verify that each key in holddups is unique, and that you do not have duplicate keys, yet unique rows. If so, you must stop here and reconcile which of the rows you wish to keep for a given duplicate key value. For example, the query:
SELECT col1, col2, count(*)
FROM holddups
GROUP BY col1, col2
should return a count of 1 for each row. If yes, proceed to step 5 below. If no, you have duplicate keys, yet unique rows, and need to decide which rows to save. This will usually entail either discarding a row, or creating a new unique key value for this row. Take one of these two steps for each such duplicate PK in the holddups table.
5. Delete the duplicate rows from the original table. For example:
DELETE t1
FROM t1, holdkey
WHERE t1.col1 = holdkey.col1
AND t1.col2 = holdkey.col2
6. Put the unique rows back in the original table. For example:
INSERT t1 SELECT * FROM holddups
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