Re: Log Switches in RAC
- From: Yong Huang <yong321@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Thu, 12 Nov 2009 09:07:58 -0800 (PST)
> There is (or was?) the concept "force archive
> SCN". I know of two sources
> where this is talked about. Rama Velpuri's
> "Oracle(8) Backup and
> Recovery Handbook" and Lawrence To's
> "Archiving Tips and Hints". The
> latter can be found at
> https://support.oracle.com/cgi-bin/cr/getfile.cgi?p_attid=75071.1:219081
If you have problems accessing that URL, just search for Note 75071.1.
Rama Velpuri actually calls it "force SCN" (without "archive"). With that
I find a couple of notes and bug reports on MOS. But the most clear
explanation is on Steve Adams's site at
http://www.ixora.com.au/notes/log_switch_triggers.htm:
"Whenever a log file is reused in any thread, the force SCN recorded
in the database entry of the controlfile is advanced to 1 beyond the
high SCN of the reused log file (unless the force SCN was already
higher). If the low SCN for the current log file in any enabled
thread thereby falls behind the force SCN, a log switch is forced
in that thread."
If you dump controlfile (alter system set events 'immediate trace name controlf
level 3'), you'll see it in the trace like this:
Arch list: Head=5, Tail=17, Force scn: 0x0007.c7f1cc74scn: 0x0007.c7f938be
Yong Huang
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