RE: Archive Mode On for Read Only DB
- From: "Gene Sais" <Gsais@xxxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 04 Mar 2004 08:01:15 -0500
Carel-Jan - Thanks for your email, but I think you misunderstood my
question :). I would never backup an open read write database and
assume its good (i.e. w/out altering tbs begin backup, etc.).
My question was: I am backing up a open READ ONLY database (using alter
database open read only, not by tbs) and questioning if archive log mode
turned on could benefit me? From some responses, it seems there is no
need to have archive mode turned on for a read only database. Thanks
for Connor's link, good stuff.
Gene
>>> cjpengel.dbalert@xxxxxxxxx 3/3/2004 4:16:49 PM >>>
At 06:18 PM 3/3/2004, you wrote:
Gene - Perhaps someone on the list has directly tried this.
Yes, I have. It's a war story with a happy ending. Last October I was
called in with a custome for one day of consultancy, discussing a
backup/restore strategy (I prefer to create a restore/backup strategy)
for a DWH they were going to setup for a customer of them.
So far, so good. The delivery day was somewhere at the beginning of
this year, but got postponed to Feb 1st.
Jan 29th I received a phone call. They accidently dropped a 300 million
row facttable. No worries I said, you have implemented the backup
strategy we discussed in October, haven't you?. 'No, we haven't, the
system isn't production yet' they answered sadly. The only thing we have
is a tar backup of an open database, created last Sunday. I discussed
the possibilities to do the restore, but somehow they didn't try and
recovered otherwise.
Wednesday Feb. 18 the phone rang: 'We were testing a database reorg and
now we've accidently dropped a multi-multi-GIG tablespace issuing 'Drop
tablespace <TS> including contents and datafiles;' After issuing the
command we discovered we were connected to the production schema ISO the
test schema'. No worries I said, this time you have enabled your
backup'. He responded: '.............' (silence). 'OK, that silence
lasts to long, what do you have'. There was a backup of an open
database, created at Monday, while the database was rebuilding indexes.
There were several logswitches whilst the backup bas made. To mak things
even worse they created the problem at Tuseday and started fiddling
around with the remains of the database without first making a proper (I
would suggest physical, i.e. dd-backup). It is all on Sun Slowaris with
Mirrored DAS. They called me in, and we worked two nights on the
subject. First night was simulating the whole situation with backing up
an open index building database, do some more work, and drop the
tablespace.
I had some phonecalls with Peter Gram and Johannes Djernaes from
Miracle. These Miracle-full guys are amazing at this.What we planned and
did was this:
Backup everything that was left ot a separate area on disk. Free up
enough space to hold the SYSTEM, UNDO, TOOLS and dropped tablespace.
Restore the mentioned tablespaces from the Monday tape with the open
backup. We were lucky: there was a controlfile more recent than the
datafiles of these tablespace on the tape Startup mount the database
ALTER DATABASE DATAFILE # OFFLINE for all unrestored datafiles RECOVER
DATAFILE # for all restored datafiles ALTER DATABSE OPEN. This worked,
and now this tablespace was available again. After some struggling with
constraints/indexes causing the tablespace not to be selfcontained the
tablespace was exported using the transportable tablespace feautures.
Next steps were: Backup the transported tablespace to another disk
Restore all datafiles/controlfiles/redologfiles that were backupped
during the first step Startup this database Import the restored
tablespace At this point, theoratically one can start rebuilding
indexes/re-enabling constraints.
Just to stay on the safe side, an extra tablespace was created and all
objects in the restored tablespace were moved to this tablespace.
Transportable tablespaces come with some bugs, and we wouldn't risk to
hit anyone of them. After moving all objects (inlcuding some LOB's)
indexes were recreated an constraints enabled.
Everything is fine now.
Remark: The tablespace that was dropped wasn't hit by any objects for
several days before the backup was made.
This case illustratetes my opinion that, from the view of a DBA, 'EVERY
DATABASE IS A PRODUCTION DATABASE'. Excepth maybe the test-thing on your
laptop/desktop.
The argument, that a database (or DWH in this case) hasn't reached
production state yet is stupid. What have the consultants, setting up
the database for over three months been doing then? Is development no
production? Lack of time to implement a backup-procedure is no excuse.
Maybe it is for the DBA, but it isn't for his manager.
They've learned their lesson. They called in a consultant to implement
the backup rightaway.
Regarding READONLY databases, please read also Connor McDonalds note
about slow readonly at www.oracledba.co.uk, look under Administration,
the note is from 14/06/2002
Regards, Carel-Jan
===
If you think education is expensive, try ignorance. (Derek Bok)
===
It is
theoretically possible to get a good backup on a quiet but open
database
with just a cold backup, but not the sort of thing you want to bet your
job
on. One idea would be for you to take your backup and restore it on a
test
system. It is always a good practice to test your database restore
anyway.
Then you would be assured throughout the year that you do indeed have
a
valid backup. But I would do it each year since there might be some
condition that would make the backup succeed 50% of the time, you would
be
covered all the time.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams@xxxxxxxxxxxxx
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On
Behalf Of Gene Sais
Sent: Wednesday, March 03, 2004 10:12 AM
To: oracle-l@xxxxxxxxxxxxx; DENNIS WILLIAMS
Subject: RE: Archive Mode On for Read Only DB
Dennis - The database is opened in read only mode. The database
changes
once a yr to be updated w/ new images. At that time, I put the db in
read
write mode, add the images, then open db in read only and back it up
while
db is open. It is a web query db that I would like to minimize down
time.
Is there any benefit to putting this db in archive log mode? I don't
see
any, but I may be missing something :).
Thanks for your help,
Gene
>>> DWILLIAMS@xxxxxxxxxxxxx 3/3/2004 10:47:26 AM >>>
Gene - By read only, do you mean the contents of the database are
never
changing? Do you ever take it out of read only mode, like to change
something? Why back it up occasionally? Just do a cold backup once and
save
the tapes.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams@xxxxxxxxxxxxx
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [
mailto:oracle-l-bounce@xxxxxxxxxxxxx]On
<mailto:oracle-l-bounce@xxxxxxxxxxxxx]On>
Behalf Of Gene Sais
Sent: Wednesday, March 03, 2004 9:04 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Archive Mode On for Read Only DB
I have an 8i read only database that is used for query of images.
Occassionally, I back it up using OS utilities (cp, tar, TSM, etc)
while the
db is open.
Question: Is there any benefit to having this db in archive log mode?
Since
it is in read only mode, I see no benefit or am I missing something?
Thanks for any insight you may provide,
Gene
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