RE: Current Redo got deleted
Date: Tue, 24 Mar 2015 10:05:38 -0400
Message-ID: <29cb01d0663b$9c40cb20$d4c26160$_at_rsiz.com>
Okay, so the first step of RECOVERY is to back up the online redo logs and the controlfile. (There is a religious war about whether online redo should be in routine backup sets centering on risk having some complete archive even if someone does something stupid, like delete the online redo logs, versus the risk of stupidly restoring old online redo logs over the top of the current online redo logs [which might be the only place the latest commits survive]).
Backing up the online redo logs and the controlfile as part of RECOVERY, however, is the only way I know of that allows you to try again from the current state if during the RECOVERY attempt you encounter something unexpected (which includes anything, but common examples are additional hardware glitches and software bugs) or a problem exists between the keyboard and the chair (PEBKAC).
Since you’ve already lost your online redo logs this bit of the RECOVERY is reduced to your controlfile.
I’d make two for anything important to two isolated stores, preferably at least one of which is physically removable and can be put beyond the reach of whoever started this circus.
The next bit is a physical backup of all the datafiles. It is a good idea to have a list somewhere that is not down when your database or server is down. Just like your long term performance repository should not use production cycles, your information to facilitate RECOVERY should not be in a single location nor dependent on a single point of failure.
Old school we would use triplex raid images (translation: when folks write “mirror” they usually mean duplex, and each “image” is plex. Triplex means you have three plexes defined and you usually have a least duplex active all the time but have the capability to detach a plex or reassociate a plex to the overall volume image (aka as “resilvering” in the mirror metaphor).
New school you use something like EMC timefinder, and even newer school something like Delphix.
Doing this quickly revolves around non-RMAN physical backup. (which may be built into some packaged solutions.)
Then I’d try the step Tim Gorman mentioned. You may in fact find that everything in the last used online redo log was archived before the retries to switch through all the remaining missing logs resulted in a hang or crash. Since lgwr had your last current online redo log open, any reasonable operating system would prevent the data going “poof!” due to a deletion until it is closed.
IF you have an expert on your storage media handy, it may still be possible to locate the file’s extent map at the operating system level and use OS level utilities to copy the correct physical blocks to construct a new image. Before they play games, read the bit about preserving the existing state above.
OH and look in your recycle bin (or the analog to a recycle bin). Your lost online redo might be there just waiting to be retrieved. Just be careful about the recycle of the one that was currently being written – the possible options depending on OS implementation beggar the imagination.
Good luck.
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Ram Raman
Sent: Monday, March 23, 2015 11:36 PM
To: kaygopal_at_gmail.com
Cc: dba.tyagisumit_at_gmail.com; Oracle L
Subject: Re: Current Redo got deleted
Wonder how the step #2 "MAKE A COMPLETE BACKUP of CURRENT STATE OF THE DATABASE" will work in the case of a big database where backing up the current state might take a long time. Especially when the users are screaming in the ears to get things up ASAP.
On Sun, Mar 22, 2015 at 4:48 PM, K Gopalakrishnan <kaygopal_at_gmail.com> wrote:
Sumit--
1..OPEN AN SR -- SEV-1 with Oracle Support
2....MAKE A COMPLETE BACKUP of CURRENT STATE OF THE DATABASE
- Try to mimic an incomplete recovery -- Recover database using backup control file
- You can either use '_allow_resetlogs_corruption=true' and try opening the db with resetlogs
- alter database open reset logs;
- Rebuild the database --probably with datapump/ export
- Duplex the redologs / run the db in archive log mode.
Sent from my iPhone
On Sun, Mar 22, 2015 at 12:31 PM, sumit Tyagi <dba.tyagisumit_at_gmail.com> wrote:
Hi Guys ,
How to deal with this " Current redo got deleted & DB crashed " . What are the option we have as a DBA
--
BR
Sumit Tyagi
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Received on Tue Mar 24 2015 - 15:05:38 CET