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Re: Confusion why online redo logs should never be backed up.

From: Tim Gorman <tim_at_sagelogix.com>
Date: Mon, 26 May 2003 10:31:41 -0800
Message-ID: <F001.005A2B29.20030526103141@fatcity.com>


Having just watched the movie "Mystery Men" with my kids last night, I thought I'd channel the Sphinx for a moment:

    "Backing up in order to recover, is less important than     recovering what was backed up."

...and for those who prefer to channel the Spleen, "Pssssssssssst!"... :-)

on 5/26/03 4:26 AM, Richard Foote at richard.foote_at_bigpond.com wrote:

> Hi Hemant,
> 
> I appreciate you're comments but I honestly haven't missed Jared's point and
> I remain unconvinced. I just don't accept the argument that such backups are
> warranted in case of junior DBA inabilities to perform clean backups or open
> with resetlogs. "Junior DBAs" in charge of important production databases
> that can't do the above are the issue, not the backup strategy. They're just
> as likely to overwrite the current online logs with the backups during a
> normal recovery or lock themselves in the toilet or some such ;)
> 
> Then again, it might serve the organisation right for employing such DBAs
> based only on OCP credentials !!
> 
> Cheers ;)
> 
> Richard
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> Sent: Monday, May 26, 2003 2:21 AM
> 
> 

>>
>> Richard,
>>
>> I think that you are still missing Jared's point.
>> It is quite right of you to say that a DBA should do a consistent backup
>> and that
>> one who does not run his backups properly is committing a sin.
>>
>> Jared has already explained two examples of why you would want the online
>> backups
>> included in a Cold Backup. And I reiterate them here.
>>
>> 1. On Windows, the Stop Oracle Service doesn't always do a SHUTDOWN
> NORMAL

>> or SHUTDOWN IMMEDIATE. See Bug 1568668
>> "With releases 8.1.5 and 8.1.6 stopping the database via the
>> services, shuts the database down immediate, whereas 8.1.7
>> kills the process. This means recovery is always required on
>> startup and customers backup strategies my become invalid.
>> If a customer takes cold backups without redo they will not
>> be able to open the database. "
>> So what happens if you have a database that hasn't been patched and you
>> or your colleague or the previous DBA had been happily using the Stop
> Service

>> and backing up the database without the online redo logs and one day you
>> need to recover the database and ..... uh oh ! "Hey ! Why does Oracle
>> ask for the redo log file ?!"
>>
>> 2. You are a consultant or a service provider or are implementing a
> system

>> for a customer and ask the customer to send you a backup of his database.
>> The SA or the trainee-DBA executes a SHUTDOWN ABORT and send you the
> database

>> files [he might say "I did try a SHUTDOWN but it was 'hanging' for
>> 10minutes so I
>> finally killed it and ran a SHUTDOWN ABORT before backing up the
> database"]

>> Always insist that the person at the other end sends you a full backup,
>> including
>> online redo logs and the init<SID>.ora.
>> [Of course, instead of the other person being a customer's SA or
> trainee-DBA

>> he could be your own colleague [SA/trainee-DBA/Damager] with whom you have
>> split the
>> responsibility of managing the 50 or 100 odd databases in your enterprise
>> or the backup scripts
>> may have been written by the former DBA and, although you have reviewed
>> and verified or fixed 99 backup scripts in your first 5 days, the 100th
>> database
>> crashes on your 6th day on the job].
>>
>>
>> I always run a switch logfile or archive log current before backing up
> archive

>> logs in a Hot Backup but do not backup online redo logs with the Hot
> Backup.

>> With a Cold Backup I always backup the online redo logs as well. [Tough
> luck

>> for me if I join an organisation and I am the guy that got hit on that 6th
> day

>> because the previous DBA's scripts weren't doing a proper shutdown].
>>
>> Also, although many DBAs know that you can bring up a properly shutdown
> and

>> backed up cold database without the online redo logs as they know the
>> OPEN RESETLOGS command, not all DBAs know this. Suppose the
>> person is a trainee-DBA or an SA or a Damager. He's going to curse
>> Oracle when he finds that he can't bring up his database although he
>> did a "complete" backup [using the guidance provided in the 9iR2 manual
>> which so helpfully told him not to backup the online logs but he has never
>> read about how and when to run an OPEN RESETLOGS].
>>
>> Therefore, the advice NOT to backup online redo logs is patently
> dangerous.

>>
>> The advice should be to backup online redo logs already on disk before
>> beginning a restore. In fact, that is always a standing instruction in
> any

>> Oracle Database recovery -- backup what you currently have on disk,
>> no matter how badly "hosed" before you begin the recovery.
>>
>> Hemant
>>
>>
>>
>> At 04:56 AM 25-05-03 -0800, you wrote:
>>>> Richard,
>>>> 
>>>> You must have missed one. :)
>>> 
>>> Hi Jared,
>>> 
>>> I think we're going to have to introduce quotas, no more than two
>>> contributions per thread ;)
>>> 
>>>> 
>>>> There have been 2 occasions where someone has
>>>> sent me 200 gb worth of database on tape, and
>>>> the database had not been shutdown properly.
>>>> 
>>>> Since the system datafile needed recovery from
>>>> the online logs, I was very glad to have them.
>>> 
>>> I guess my point is that making a backup without shutting down the system
>>> properly is a sin akin to scratching a rare David Bowie LP, ie. somewhat
>>> unforgivable (although I admit the second sin is far worse). Make a
>>> consistent backup and/or have the database in archivelog mode, you then
>>> don't require the online redo logs ....
>>> 
>>>> 
>>>> I have encountered this on a very few other
>>>> occasions, but can't recall the circumstances
>>>> of those events.
>>>> 
>>>> They are also useful when cloning a DB (without RMAN),
>>>> though not required.  Depends on how the clone
>>>> will be used.
>>> 
>>> I guess my point here is the "though not required" bit. It simplifies the
>>> process I agree but even in this case, the online logs are not strictly
>>> required.
>>> 
>>>> 
>>>> As with many things, this is not a black and white
>>>> issue.  There are shades of gray.  While it certainly
>>>> not necesssary to normally backup the online logs
>>>> during a cold backup, it is incorrect to say that
>>>> they are never useful.
>>>> 
>>> 
>>> I guess we're going to have to agree to disagree. However, getting back
> to
>>> the subject of sins, including online redo logs in a cold backup is not
>>> really an issue that would cause me loss of sleep (unlike scratching DB
>>> LPs). Like, it doesn't really hurt. But if someone were to accidentally
>>> incorrectly restore them in a recovery scenario, ouch, that would be a
> sin
>>> worth having a chat about ;)
>>> 
>>> Cheers
>>> 
>>> Richard
>>> 
>>> 
>>> --
>>> Please see the official ORACLE-L FAQ: http://www.orafaq.net
>>> --
>>> Author: Richard Foote
>>>   INET: richard.foote_at_bigpond.com
>>> 
>>> Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
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>>
>> Hemant K Chitale
>> Oracle 9i Database Administrator Certified Professional
>> My personal web site is : http://hkchital.tripod.com
>>
>>
>> --
>> Please see the official ORACLE-L FAQ: http://www.orafaq.net
>> --
>> Author: Hemant K Chitale
>> INET: hkchital_at_singnet.com.sg
>>
>> Fat City Network Services -- 858-538-5051 http://www.fatcity.com
>> San Diego, California -- Mailing list and web hosting services
>> ---------------------------------------------------------------------
>> To REMOVE yourself from this mailing list, send an E-Mail message
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>>

>
-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Tim Gorman
  INET: tim_at_sagelogix.com

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Received on Mon May 26 2003 - 13:31:41 CDT

Original text of this message

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