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Home -> Community -> Usenet -> c.d.o.server -> Re: Online backup: Backup online redologs?
On Mon, 7 May 2001, Spencer wrote:
> the risk that an "old" backup copy of an online redo log
> will be "restored" over top of a perfectly good online
> redo log file, which could very well "wipe out" valid redo
> entries that are needed for complete recovery.
> so, including "backup" copies of online redo log files in
> a "hot backup set" is of dubious value... since the backup
> copy of the online redo log file should never be restored,
> is not just useless, it is downright dangerous.
> when the pressure is on to get the database files restored
> and the database recovered, how are you going to make
> sure that the junior dba restores ONLY datafiles and does
> NOT restore the online redo log files ? having the backup
> copies of the files available only raises the risk that these
> files will be restored. Yikes!
I have 3 reasons why I am going to reject your argument on what I consider to be extremely valid grounds.
Number one:
You probably didn't notice the following SQL in my backup script:
# The ugly SQL below selects only a single member from each group. print -p "$CONNECT
set sqlprompt ''
set sqlnumber off
set trimout on
set head on
set pagesize 2048
set linesize 2048
SELECT
'+ '|| RTRIM(x.member)
FROM
v\$logfile x
WHERE
x.member IN
(
SELECT
member
FROM
v\$logfile
WHERE
group# = x.group# AND rownum < 2
);
quit"
ASSUMING that each log group has dual members, this code is only going to select for hot backup a SINGLE member, so that is all that is going to be available for my impetuous junior dba to restore. Granted, one of the members might have been lost, and this might overwrite the only remaining good member. HOWEVER, if archive logs still exist, then the recovery will be complete until the last log switch.
Also, my script dumps copies of all the data into a single $DEST directory. If the system is laid out under OFS guidelines, then it will be impossible to wipe out both log members just by doing a simple restore from tape.
Number two:
What if the server catches fire? What if some idiot spills a coke into the disk array? What if we have a tornado and I see my server sailing past my office window?
It might be a tad difficult to extract the online redo logs in that case.
I ABSOLUTELY MUST have everything that I need to restore the database on a tape that I can hold in my hand, and it must be from a hot backup. If I can't have that, then I don't want Oracle (and I don't know why anybody else would).
I don't know why there isn't a furious uproar of people asking the same set of questions about this that I am. I just don't understand it.
Number three:
I need to clone from time to time from our production to development systems. My backup method works great double-duty.
p.s. There is actually a case where I could get stung pretty badly by this procedure. If when I start copying the redo logs, the active log group is the LAST log group, and it is nearly full, and granted that I get a complete copy of the first log group, but also granting that before I get to the last log group, a log switch occurs, then there will be no active log group in the backup set, and my goose will be cooked when I try to restore. However, things are pretty quiescent when I am doing this, but maybe I ought to look into forcing the first log group to go active before I take the hot backups.
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