RE: What happens during open resetlogs?
- From: Tanel Poder <tanel.poder.003@xxxxxxx>
- To: veeeraman@xxxxxxxxx
- Date: Thu, 24 Aug 2006 12:46:54 +0800
That's normal, SCN for a database is ever-increasing, you can not roll it
back even with RESETLOGS open. The RESETLOGS_CHANGE# will be set to current
SCN during a RESETLOGS operation.
Only the log sequence numbers are reset to zero due RESETLOGS, not SCN. And
the log sequence number is something which resides in controlfile, not
datafile headers. Internally only the SCN's matter for deciding whether a
log is needed for recovery or not, log sequence numbers are here just for
our convenience again.
If Oracle did reset the database SCN back to zero during RESETLOGS then we
would have to go through every block in datafiles and reset the last update
SCN in their headers back to zero as well, lot's of functionality is
dependent on that info. Also, all undo segments would need to be reset, etc.
Even when you plug a transportable tablespace with much higher SCNs in to
your database, then Oracle has to bump up SCN to match the highest SCN in
the datafile headers.
Oracle doesn't ever reset SCN back for a database, it's only the changed
RESETLOGS_CHANGE# which determines a new incarnation of the database, all
other things going on are done just for our convenience...
Tanel.
_____
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Ram Raman
Sent: Thursday, August 24, 2006 04:37
To: tanel.poder.003@xxxxxxx
Cc: alever@xxxxxxxxx; oracle; oracle-l
Subject: Re: What happens during open resetlogs?
I recently cloned and opened a database with resetlogs option. I thought I
would find the RESETLOGS_CHANGE# to be something like 1 or 10, instead I
found it to be some 17 digit number carried over from production. Any
thoughts on that.
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