Comments on: SCN – What, why, and how?

By: Riyaj Shamsudeen

Riyaj Shamsudeen — Mon, 03 Jun 2013 15:25:58 +0000

Hello Hrishikesh
I don’t understand your question. What is not working? Please describe the problem.
Thanks for reading
Cheers
Riyaj

By: Hrishikesh

Hrishikesh — Mon, 03 Jun 2013 06:03:39 +0000

Hi,
I want to alter below SCN parameters , but it’s not happening.Help is much appreciated
=============
_external_scn_logging_threshold_seconds= 600;
_external_scn_rejection_delta_threshold_minutes= 10080;
================
I used below alter command to set the parameters, but it’s not helping out
SQL> alter system set “_external_scn_logging_threshold_seconds”= 600 comment=’Set threshold on 31/05/2013 – See SR#497386-326095900′ scope=spfile;

System altered.

SQL> alter system set “_external_scn_rejection_delta_threshold_minutes”= 10080 comment=’Set threshold on 31/05/2013 – See SR#497386-326095900′ scope=spfile;

System altered.

SQL>

Thanks,
Hrishi

By: Riyaj Shamsudeen

Riyaj Shamsudeen — Wed, 17 Apr 2013 20:11:31 +0000

Hello Udit
There is no specific number of SCNs generated for a DDL command such as create table, create index etc. It depends upon many variables, such as table definition, index definition, data etc.

Cheers
Riyau

By: udit

udit — Wed, 17 Apr 2013 18:10:21 +0000

how many times scn generated during create command….thks in adv …

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By: Riyaj Shamsudeen

Riyaj Shamsudeen — Wed, 18 Apr 2012 17:08:31 +0000

Hello Robert
Yes, that’s correct. That’s the infamous 31-day bug. Oracle code assumes 31 days while calculating number of seconds elapsed from 1-1-1989. This does not mean that Oracle Date calculation is incorrect, it is just an code optimization to calculate elapsed seconds quickly.

Cheers
Riyaj

By: Robert

Robert — Wed, 18 Apr 2012 10:16:43 +0000

Hello Riyaj,

col current_scn format 99999999999999999999999
col maxscn format 9999999999999999999999
select
dbms_flashback.get_system_change_number current_scn,
((
((to_number(to_char(sysdate,’YYYY’))-1988)*12*31*24*60*60) +
((to_number(to_char(sysdate,’MM’))-1)*31*24*60*60) +
(((to_number(to_char(sysdate,’DD’))-1))*24*60*60) +
(to_number(to_char(sysdate,’HH24′))*60*60) +
(to_number(to_char(sysdate,’MI’))*60) +
(to_number(to_char(sysdate,’SS’)))
) * (16*1024)) maxscn
from v$instance
;

In your Query ‘maxscn’ ist calculated fix with 31 Days per month over timeperiod – is this the way oracle calculates the ‘scn softlimit’ ?
We have calculated with the real count of Days per month over timeperiod – is this wrong?

VG
Robert

By: Riyaj Shamsudeen

Riyaj Shamsudeen — Thu, 29 Mar 2012 22:09:35 +0000

Hello Andrey
A SGA variable array keeps track of the state at a file level. Meaning, each file has 8 bytes allocated in the SGA and the status of backup mode is indicated in that byte.

Cheers
Riyaj