NotesFromClass-BackUP & Recovery

From: Bruce Walker <rbwalker1_at_mindspring.com>
Date: Sun, 25 Mar 2001 19:56:59 -0500
Message-ID: <3ABE93DB.5843E09D@mindspring.com>

To All - I am taking a class for OCP Oracle 8i. These notes are a reflection of my classroom teaching and are published here to receive feed back from 'professionals' who do the job I am training for now. any and all input is appreciated for clarity.

this week 03/25/2001 * BACKUP & RECOVERY **

commit is the most prevalent event to write from redo log buffer to redo log files
thru the log writer LGWR.

fast start begins to empty the datablocks (dirty)from the db buffer to dbase datafiles.

lgwr is most active process. Writes all the time. original and mirror makes one group. there are at least two groups.

for each block from redo log buffer that is written, each file in the group gets a duplicate of the other.

DBWR, LGWR, ARCH defines OFA Optimal Flexible Architecture simply saying the 3 processes don't block/lock up each other.

this means put them on different disks. when you put them on the same drive, they conflict.

log switch causes a checkpoint.checkpoint induced by log switch EXCESSIVE I/O FAST_START_IO_TARGET = 20 block size is 8k, redo log size is 320k, which means you have 40 blocks.

every 20 blocks it will write to redo log files, CHECKPOINT.

redo log buffer works cyclically.
when checkpoint kicks in, goes point a to point end. it is sequential. this, I was told, is important. the fact it is sequential.

SMON is in charge of instance recovery------------------

instance recovery SMON

roll forward -
committed - in redo log file
not sychronized -
will OPEN database

roll back
not committed -
sychronized
you will not be looking for something you didn't commit. I need a little elaboration on this part.

once you enable archive log mode, there must be space in archive log folder. Automatic archiving is important, you must turn it on. with NO archive log mode, there is NO recovery.

configure archiving
manage space in archive folder - with no space for archives oracle will HANG. waiting for you.
Is this true, will stop the system dead in its tracks?

BUSINESS      Online backup     offline backup 
24 x 7        warm              cold 
8am - 5pm      oracle is        oracle is 
               up & running     down & cold

oracle should be in archive log mode.

recover automatic database;

every file has a header record. those files without an up to date header record, oracle will figure it out. those files that are out of synch will be recovered.

restore only required data files
if oracle did not shutdown, recover in opened mode.

in a crash
- how many files are involved ??

what files do I need for recovery ??

must restore datafile

Investigate
startup PFILE='d:\path\init.ora' MOUNT

 V$RECOVER_FILE 
 V$RECOVERY_LOG 
 v$datafile

if file status is ONLINE, then take it OFFLINE alter database datafile 2 OFFLINE

never restore on a file that is NOT OFFLINE

recovery process
1 restore datafiles
2 recover automatic database;
3 bring back file ONLINE

system tablespace is important for DATA DICTIONARY. so you cannot recover online. you must take this offline. this coincides with a shutdown.

a file number is consistent with the file for the life of that file. It won't change.

DON'T put your REDO logs on a RAID array. as the redo logs are sequential.
could someone elaborate on this....

Can you recover if you cannot restore ? Received on Sun Mar 25 2001 - 18:56:59 CST