SCN Number

Hi,
When is the SCN number exactly generated. I read that it is generated when commit happens. If that is the case. How does oracle know that (when rolledback) which transaction to roll back. I mean how does it monitor all the transactions ( Both commited and uncommited).
Thanks
Rakesh

user8697235 wrote:
I am aware of that part. My question was, how does Oracle keeps track of uncommited transactions?
Rakesh,
You don't need to worry about the SCN, oracle will take care of it. About the uncommitted transactions,there are couple of places where oracle keeps this info that the transaction is still alive. The very first is the transaction header of the data block where this info is alive that the status of the transaction is still Active. Also, the buffer's status is marked by oracle as dirty thus tells to the the dataabase that the buffer is no more consistent. The second place where this info is kept and also, from where its cleared in the first place when the tranaction gets over ( irrespective of commit/rollback) is the transaction table which is kept in the Undo segment header . In each of the undo segment , this info is kept and that's the place where Oracle finally goes and confirms that whether the transaction is still alive or not. And how oracle knows which undo segment to go, its kept in the transaction header in the form of the undo byte address (UBA) .
HTH
Aman....

Similar Messages

How to get the last SCN number from catalog database

Hi All,
I have a catalog database where my PROD database is registered. Evereyday at 12AM rman takes the hot backup of PROD.
Now I want to create a auxillary database using the last RMAN backup, for this I want to restore using the SCN from the catalog views.
Please help me to get the SCN number from the RC_ views.
Regards,
Bikram

asifkabirdba wrote:
Current SCN:
Use the dbms_flashback package to get the current SCN. This value will be used during instantiation at the destination site, as well as by RMAN when duplicating the database.
SET SERVEROUTPUT ON
DECLARE
until_scn NUMBER;
BEGIN
until_scn:=
DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER;
DBMS_OUTPUT.PUT_LINE('Until SCN: ' || until_scn);
END;
Regards
Asif KabirHello,
i am a bit confused,
SELECT CURRENT_SCN FROM V$DATABASE;
6272671324
and from your package
SET SERVEROUTPUT ON
DECLARE
until_scn NUMBER;
BEGIN
until_scn:=
DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER;
DBMS_OUTPUT.PUT_LINE('Until SCN: ' || until_scn);
END;Until SCN: 6272671267
why are they different, and why first result is lower than yours? can you explain please, thank you
Ugur MIHCI

How can I determine what is the minimum SCN number I need to restore up to.

Say if I have a full database backup, I know I have file inconsistency, but I want to know what is the minimum time or SCN number a need to roll forward to in order to be able to open the database?
For example: I do a database restore.
restore database ;
RMAN> sql 'alter database open read only';
sql statement: alter database open read only
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of sql command on default channel at 03/16/2009 15:00:04
RMAN-11003: failure during parse/execution of SQL statement: alter database open read only
ORA-16004: backup database requires recovery
ORA-01194: file 1 needs more recovery to be consistent
ORA-01110: data file 1: '/u01/oradata/p1/system01.dbf'
I need need to apply archive log files. All references I find for ORA-00194 state the solution is to "apply more logs until the file is consistent " But "HOW MANY LOGS", or more apporaite up to what time or SCN? How does one determine what TIME or SCN is required to get all file consistent?
I thought this query might provide the answer, but it doesn't
select max(checkpoint_change#)
from v$datafile_header
MAX(CHECKPOINT_CHANGE#)
7985876903
--It applies a bit more redo, but not enough to make my datafiles consistent.
recover database until SCN=7985876903 ;
Starting recover at 03/16/09 15:04:54
using channel ORA_DISK_1
using channel ORA_DISK_2
using channel ORA_DISK_3
using channel ORA_DISK_4
using channel ORA_DISK_5
using channel ORA_DISK_6
using channel ORA_DISK_7
using channel ORA_DISK_8
starting media recovery
channel ORA_DISK_1: starting archive log restore to default destination
channel ORA_DISK_1: restoring archive log
archive log thread=1 sequence=18436
channel ORA_DISK_1: reading from backup piece /temp-oracle/backup/hot/p1/20090315/hourly.arch_P1_47353_681538638_1
channel ORA_DISK_1: restored backup piece 1
piece handle=/temp-oracle/backup/hot/p1/20090315/hourly.arch_P1_47353_681538638_1 tag=TAG20090315T041716
channel ORA_DISK_1: restore complete, elapsed time: 00:02:26
archive log filename=/u01/app/oracle/flash_recovery_area/P1/archivelog/2009_03_16/o1_mf_1_18436_4vxd81yc_.arc thread=1 se quence=18436
Oracle Error:
ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below
ORA-01194: file 1 needs more recovery to be consistent
ORA-01110: data file 1: '/u01/oradata/p1/system01.dbf'
I've discover I need to apply archive logs until this query reports all datafiles as FUZZY=NO , but this only works by guessing at some time periord to roll forward to, then checking the FUZZY column, and try again. Is there a way to know, I have to roll forward to a specific SNC in order for all my datafiles to be consistent?
select file#
     , status
     , checkpoint_change#
     , checkpoint_time
     , FUZZY
     , RECOVER
,LAST_DEALLOC_SCN
from v$datafile_header
order by checkpoint_time
Thanks,
Jason

The minimum point in time is the time when the last backup piece for datafiles in that backup was completed.
Your alert.log should show the redo log sequence number at that time.
You can query V$ARCHIVED_LOG and get the FIRST_CHANGE# of the first archivedlog generated after that backup piece completed.
A
LIST BACKUP;in RMAN should also show you the SCNs at the time of the backups.
You can also query SCN_TO_TIMESTAMP -- eg
select timestamp_to_scn(to_timestamp('15-MAR-09 09:24:01','DD-MON-RR HH24:MI:SS')) from dual;will return an approximation of the SCN.
Hemant K Chitale
http://hemantoracledba.blogspot.com
Edited by: Hemant K Chitale on Mar 17, 2009 9:41 AM
added the LIST BACKUP command from RMAN.

SCN number showing unknown intigers

Hi,
I was checking the scn number of both Primary and Standby database and got this value
SQL> select current_scn from v$database;
CURRENT_SCN
5.9654E+12
How to make is in correct format?

Richa wrote:
Hi,
I was checking the scn number of both Primary and Standby database and got this value
SQL> select current_scn from v$database;
CURRENT_SCN
5.9654E+12
How to make is in correct format?
SQL> select current_scn from v$database;
CURRENT_SCN
3.5255E+10
SQL> SET NUMWIDTH 20
SQL> /
CURRENT_SCN
35254650995http://docs.oracle.com/cd/E11882_01/server.112/e16604/ch_twelve040.htm#SQPUG094
Thanks,
Hussein

About SCN number generation

Hi all,
1.what is SCN number?
2.when it will happens?
3.when will happen to commit single transaction?
4.which BG process write the SCN to each transaction?
Thanks in advance.

jp wrote:
Hi all,
1.what is SCN number?System Commit Number, a no which is incremented with every commit.
2.when it will happens?
Almost all the time.
3.when will happen to commit single transaction?No idea what you mean here!
4.which BG process write the SCN to each transaction?Not everything is done by a process. SCN is a mechanism in its own.
Search this forum for many discussions about the same topic. There are MANY threads about it.
HTH
Aman....

Find SCN number of a transaction

Is it possible to find SCN number of a transaction made yesterday?

Hi,
I guess you are using atleast oralce 8i and if your answer is yes you can use oralce new utility called logminer.if you want to know the exact scn of the particular trancation you can use v$logminer_contents view to get the desired scn,but prior of that you need to execute some steps to get your logminer work.
thanks
Alok ....

SCN Number of DDL Statements

Hi Gurus
I m using Oracle 10G R2 in Unix. Can you please tel me how to get the scn number and its corresponding DDL and grant Statement executed in a database?
Thanks
Ram

If you audit, you can select the statement and scn from aud$.
1 select scn, sqltext from aud$
2* where sqltext is not null
SYS AS SYSDBA@dummy1> /
       SCN
SQLTEXT
    677135
create table test1 (id integer)
SYS AS SYSDBA@dummy1> select current_scn from v$database;
CURRENT_SCN
     677178
SYS AS SYSDBA@dummy1> select sys.dbms_flashback.get_system_change_number from dual;
GET_SYSTEM_CHANGE_NUMBER
                  677179

Current scn number

how to get the current scn number.i m not using flashback.

You can also use Log Miner to get the SCN corrosponding to DML or DDL , which I think you looking to use , may be for some recovery purpose.do let us know the purpose of knowing the current SCN.
hare krishna
Alok

To find SCN number in standby database with Oracle 9i.

Hi all,
1.how to find SCN number in standby database with Oracle 9i.
note:
1.it is in mount stage.
2.oracle 9i.
regards,
Jayaprakash.

Hello;
I have no Data Guard 9 to review. However I might try this :
select * from "_DBA_APPLY_PROGRESS";
OR
select time_mp,time_dp, scn_wrp, scn_bas, scn from smon_scn_time;Also found this: ( almost certainly NOT a physical Standby )
SELECT APPLIED_SCN, NEWEST_SCN FROM DBA_LOGSTDBY_PROGRESS;Best Regards
mseberg
Not worth another post but I think v$database on Oracle 9 has these columns only :
v$database on Oracle 9
DBID
NAME
CREATED
RESETLOGS_CHANGE#
RESETLOGS_TIME
PRIOR_RESETLOGS_CHANGE#
PRIOR_RESETLOGS_TIME
LOG_MODE
CHECKPOINT_CHANGE#
ARCHIVE_CHANGE#
CONTROLFILE_TYPE
CONTROLFILE_CREATED
CONTROLFILE_SEQUENCE#
CONTROLFILE_CHANGE#
CONTROLFILE_TIME
OPEN_RESETLOGS
VERSION_TIME
OPEN_MODE
PROTECTION_MODE
PROTECTION_LEVEL
REMOTE_ARCHIVE
ACTIVATION#
DATABASE_ROLE
ARCHIVELOG_CHANGE#
SWITCHOVER_STATUS
DATAGUARD_BROKER
GUARD_STATUS
SUPPLEMENTAL_LOG_DATA_MIN
SUPPLEMENTAL_LOG_DATA_PK
SUPPLEMENTAL_LOG_DATA_UI
FORCE_LOGGING              ."_DBA_REGISTERED_ARCHIVED_LOG" has a "NEXT_SCN"
Edited by: mseberg on Dec 19, 2011 10:03 AM
Edited by: mseberg on Dec 19, 2011 10:29 AM
Much later
Also found this :
select dbms_flashback.get_system_change_number scn from dual;
Edited by: mseberg on Dec 19, 2011 11:06 AM

Checkpoint number and SCN number

Hi,
I am getting confused between these two terminology, i have asked a couple of people and every where i get different explanation.
Can anyone please clarify these -
a) Is checkpoint point number and SCN number same kind of number (SCN# will be greater than checkpoint#)?
b) I was told that checkpoint also gets incremented when log switch happens, but when I issue alter system switch logfile, the checkpoint_change# in v$database does not get incremented. It gets incremented when i issue alter system checkpoint
Thanks in advance
Neel

816153 wrote:
Thank you all.
Can someone help me understanding - why checkpoint_change# of v$database does not get incremented when i issue "alter system switch logfile"?
What do you think can be the reason? Let's hear from you first. And by the time you prepare the answer, please have a read of this pdf as well,
http://prutser.files.wordpress.com%2F2008%2F12%2Fcheckpointsukoug.pdf
HTH
Aman....

Max SCN Number in redolog file

Hi ,
I have configured a data guard environment using below configuration
STANDBY TYPE : - PHYSICAL STANDBY
LOG TRANSPORT SERVICE : - ARCH [ ARCHIVE PROCESS ]
STANDBY LOG :- NO STANDBY LOG IN PRIMARY AND STANDBY
SYNC STATUS OF PRIMARY AND STANDBY : - FULLY SYNC
OPERATION : - FAIL OVER USING 'ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;'
ACTIVATING THE STANDBY USING ' ALTER DATABASE ACTIVATE STANDBY DATABASE;'
PRIMARY AND STANDBY ARE IN FULLY SYNC
ON PRIMARY
LAST ARCHIVED SEQUENCE NUMBER IS 12 AND FIRST AND LAST SCN ASSOCIATED WITH SEQUENCE 12 IS AS BELOW
SELECT SEQUENCE#,FIRST_CHANGE#,NEXT_CHANGE# FROM V$ARCHIVED_LOG WHERE SEQUENCE#=12;
SEQUENCE# FIRST_CHANGE# NEXT_CHANGE#
12 669447 670246
ON STANDBY
THE ARCHIVE LOG WITH SEQUENCE NUMBER 12 HAS ARCHIVED AND APPLIED ON STANDBY DATABASE SUCCESSFULLY.
NOW I AM DOING A FAIL OVER BY USING THE BELOW COMMANDS
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
ALTER DATABASE ACTIVATE STANDBY DATABASE;
ALERT LOG ON STANDBY DATABASE
Media Recovery Log /data/PRD_DR/arch/arch_1_11_834360625.arch
Media Recovery Log /data/PRD_DR/arch/arch_1_12_834360625.arch
Media Recovery Waiting for thread 1 sequence 13
Error 12154 received logging on to the standby
FAL[client, MRP0]: Error 12154 connecting to PRD for fetching gap sequence
Errors in file /apps/oracle/diag/rdbms/stand/PRD/trace/PRD_mrp0_7865.trc:
ORA-12154: TNS:could not resolve the connect identifier specified
Thu Dec 26 18:00:36 2013
alter database recover managed standby database cancel
Thu Dec 26 18:00:36 2013
MRP0: Background Media Recovery cancelled with status 16037
Errors in file /apps/oracle/diag/rdbms/stand/PRD/trace/PRD_mrp0_7865.trc:
ORA-16037: user requested cancel of managed recovery operation
Shutting down recovery slaves due to error 16037
Recovery interrupted!
Errors in file /apps/oracle/diag/rdbms/stand/PRD/trace/PRD_mrp0_7865.trc:
ORA-16037: user requested cancel of managed recovery operation
MRP0: Background Media Recovery process shutdown (PRD)
Waiting for MRP0 pid 7865 to terminate
Managed Standby Recovery Canceled (PRD)
Completed: alter database recover managed standby database cancel
Thu Dec 26 18:00:59 2013
alter database activate standby database
ALTER DATABASE ACTIVATE [PHYSICAL] STANDBY DATABASE (PRD)
tkcrrxms: Killing 2 processes (all RFS)
RESETLOGS after incomplete recovery UNTIL CHANGE 670246
Resetting resetlogs activation ID 1898010833 (0x712158d1)
Online log /data/PRD_DR/REDOLOG11.LOG: Thread 1 Group 1 was previously cleared
Online log /data/PRD_DR/REDOLOG21.LOG: Thread 1 Group 2 was previously cleared
Online log /data/PRD_DR/REDOLOG33.LOG: Thread 1 Group 3 was previously cleared
Standby became primary SCN: 670244
Thu Dec 26 18:01:01 2013
Setting recovery target incarnation to 3
Converting standby mount to primary mount.
ACTIVATE STANDBY: Complete - Database mounted as primary (PRD)
Completed: alter database activate standby database
IN STANDBY ALERT LOG I CAN SEE BELOW THINGS
RESETLOGS after incomplete recovery UNTIL CHANGE 670246
Standby became primary SCN: 670244
MY QUESTION IS ON 'SCN NUMBER OF 'Standby became primary SCN: 670244'.
I HAVE CHECKED THE SCN NUMBERS OF THE ARCHIVE LOG OF SEQUENCE 12 [ USING LOGMINER ] THE MAX SCN ASSOCIATED WITH THE ARCHIVE LOG IS 670242
SELECT MAX(SCN) FROM V$LOGMNR_CONTENTS; [ FOR LOGMINER I HAVE USED '
EXECUTE DBMS_LOGMNR.START_LOGMNR(OPTIONS => DBMS_LOGMNR.DDL_DICT_TRACKING + DBMS_LOGMNR.DICT_FROM_REDO_LOGS); ]
MAX(SCN)
670242
- WHY IN LOGMINER MAX(SCN) IS NOT SHOWING AS 670246 ?
- HOW I CAN SEE THE SCN 670244 FOR ARCHIVE LOG FOR SEQUENCE NUMBER 12 ?
Thanks,

IN STANDBY ALERT LOG I CAN SEE BELOW THINGS
RESETLOGS after incomplete recovery UNTIL CHANGE 670246
Standby became primary SCN: 670244
MY QUESTION IS ON 'SCN NUMBER OF 'Standby became primary SCN: 670244'.
I HAVE CHECKED THE SCN NUMBERS OF THE ARCHIVE LOG OF SEQUENCE 12 [ USING LOGMINER ] THE MAX SCN ASSOCIATED WITH THE ARCHIVE LOG IS 670242
in fact, it is really intelligent question.
First you have to know the sequence 12, next_change# is not belongs to 12 but it belongs to the 13th sequence first_change...
So in the real, the seqeunce 12 change number is only up to 670245 and the change 670246 is the starting change of sequence numebr 13.
It is not using any real time apply, Now as per the my above conclusion the sequence number last change is only 670245 , As per the recovery concepts.. If you want to perform recovery change up to 100, you need to mention as "until 100 + 1", i.e. 101.. So if you mention 101 then it performs recovery until 100.
1) the 12 sequence max change is 670245
2) when it performs recovery until that sequence, then then usually it performs recovery until 6740244 as per the recovery rules.
From http://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12033.htm
UNTIL CHANGE integer
Processes managed recovery up to but not including the specified system change number (SCN).
Still at this point am not giving conclusion 100%, am testing same as you using log miner and will let you know sure..
- WHY IN LOGMINER MAX(SCN) IS NOT SHOWING AS 670246 ?
When you analyze archive redo log file, Have you used starttime and end time? Note that if you give end time bit less then there is chance to truncate to gather information for log miner and important thing is Oracle writes checksum information and change information in terms of metadata into headers.Also note that oracle uses some of records for SYSTEM CHANGE, so some of them may not visible.
HTH.

SCN number difference in primary and standby databases

Hi All,
Is it possible that primary database SCN is 20 and standby database SCN is 22 ? If yes , how it works ?
Thankyou !

I agree that it is possible depending on your setup. However, I read your posting and BLOG entry but it does not address out the Standby database has a GREATER SCN than the Primary.
The answer will depend on the type of standby database you have configured (LOGICAL vs PHYSICIAL) and perhaps if it is a SNAPSHOT Standby that has been used and not rolledback.
In what I would consider "Normal" situations the SCN of the standby database would always either be at the same SCN or be lagging.
I have not tested it but I could see where if you had a standby database that you converted to a SNAPSHOT Standby (11g ability), made changes to the standby and had not converted it back to a normal Standby then your SCN can be ahead in the standby because the changes had not been discarded yet.
Regards.
Tim

Want to see whole SCN number instead with +E number

SQL> SELECT CURRENT_SCN FROM V$DATABASE;
CURRENT_SCN
1.0254E+13
SQL> select name,database_role,open_mode,CURRENT_SCN FROM V$DATABASE;
NAME DATABASE_ROLE OPEN_MODE CURRENT_SCN
P89889 PHYSICAL STANDBY MOUNTED 1.0254E+13
how can i see the whole number instead with +E
Thanks in advance
Edited by: Dharmesh Kumar on Aug 4, 2009 7:48 AM

SQL> column current_scn format 999999999999999999
SQL> SELECT CURRENT_SCN FROM V$DATABASE;
CURRENT_SCN
5183434

Scn and seq number

is there any difference between the scn number and the log sequence number.please say me
Regards
Aram

do NOT cross/multi-post
scn number

How can i generate a large SCN for database

Hi,
On databases where SCN number is larger that 2^32 , my application seems to work in a weird way. Am trying to get this re produced in my test setup , but am unable to pump up the SCN number to such a large value.
I am trying this on RHEL5-64 bit and WIN2003-64 bit with Oracle 11gR2 using a script which does some table creation , deletion etc.
Does any one know any method to increase the SCN value ? This would be of great help.
--Amith

Simply selecting a row from v$database, in a loop, will increase the current SCN. Don't ask me why this happens as I do not have an answer for the same.
SQL> select current_scn from v$database;
CURRENT_SCN
2944216219
1 row selected.
SQL> select current_scn from v$database;
CURRENT_SCN
2944216221
1 row selected.
SQL> select current_scn from v$database;
CURRENT_SCN
2944216222
1 row selected.
SQL>

SCN Number

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