Oracle doubt...backup/recovery

Question

Hi all,
1.Can anyone help me understand the significance of checkpoint_change# parameter in v$datafile,v$datafile_header and v$database in the context of recovery? And various situations explaining their values?
2.If anyone give me some link for practising some test cases on this I will be grateful and hope by doing the concept will be clear.
2.When do we fire "recover database using backup controlfile until cancel"?
Regards,
Saikat

Answer 1

v$database---checkpoint_change#,current_scn
checkpoint_change# is the scn number written to control file during checkppoint and current_scn is the SCN in the database at the current time.
current_scn will be ahead of checkpoint_change# as the background process do the work continuously and gets incremented. Once checkpoint occurs
both checkpoint_change#=current_scn
V$DATAFILE --checkpoint_change#  is the last SCN   recorded for each datafile when last checkpoint occured.
V$DATAFILE_HEADER---This view displays datafile information from the datafile headers.
When your db is in open mode, checkpoint_change# form v$database,v$datafile,v$datafile_header are same.
sql> select name, CHECKPOINT_CHANGE# dbcheckpoint,current_scn dbcurrscn,a.*,b.* from (select checkpoint_change# datafilechkpt, count(*) from v$datafile group by checkpoint_change#) a, (select checkpoint_change# datafilehdrckpt, count(*) from v$datafile_header group by checkpoint_change#) b,v$database;
NAME DBCHECKPOINT DBCURRSCN DATAFILECHKPT COUNT(*) DATAFILEHDRCKPT COUNT(*)
REPO 232905378354 232905387977 232905378354 5 232905378354 5
From mount to open mode of database, if checkpoint_change# in v$datafile_header and v$database does not match your database does not come to OPEN mode.
2) When you loose your current controlfile , and restore the control file from backup. In this case your checkpoint_change# from v$datafile_header would be greater than checkpoint_change# from v$database(since it is old control file) and hence it asks for recovery
Edited by: vreddy on Aug 13, 2012 10:19 AM
Edited by: vreddy on Aug 13, 2012 10:22 AM
Edited by: vreddy on Aug 13, 2012 10:22 AM
Edited by: vreddy on Aug 13, 2012 10:23 AM