RE: Split Blocks on Instance Crash

 I think the questioner is asking about the 512 byte components of the write of the Oracle block.

In a non-RMAN backup, the operating system utilities have no particular interest by default in copying chunks (n of the usually 512 byte pieces) in anything like an
alignment matching Oracle's blocks. DBWR, on the other hand, will definitely submit Oracle blocks as integral sets of the pieces that make up the Oracle blocks from the underlying OS pieces.

So the risk goes way, way down. I'd quibble slightly with Tanel's "always" remark. If you restart and it tells you media recovery is required, then a file really did get crashed and one of the cases of a file getting trashed is that it is not marked fuzzy and a block's header and tail don't match. Then you would have to get a previous backup of the file (or block) and roll it forward. So the recovery is just the same as if you lose a file for any other reason. When I've gotten a file trashed (...never on a client of mine with at least duplex plex images, but frequently in the dim past when lots of folks used single plex images) I never saw a block that looked complete except for a mismatch, so I'm thinking this is very rare.

Regards,

mwf
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Tanel Põder Sent: Thursday, December 22, 2005 10:49 AM To: ORACLE-L
Subject: Re: Split Blocks on Instance Crash

Hi,

Because in case of instance crash, you can always read the previous image of block from disk and all subsequent changes to this block can be read from online logfiles, in media failure case you might not be able to do so.

Tanel.

• Original Message ----- From: "Charlotte Hammond" To: Sent: Thursday, December 22, 2005 9:31 AM Subject: Re: Split Blocks on Instance Crash

>
> Thanks David - but why is this different from the
> backup situation? You would have the (archived) redo
> available then too, but you must still use BEGIN/END
> BACKUP to avoid split blocks.
>
> Charlotte
>
>
>
> --- David Sharples wrote:
>
>> because the information is available from redo /
>> undo and can easily be
>> replayed in case of a failure
>>
>> On 12/22/05, Charlotte Hammond
>> wrote:
>> >
>> > Hi All,
>> >
>> > Why does instance crash recovery not encounter the
>> > split blocks that you might get doing a backup
>> without
>> > BEGIN/END BACKUP?
>> >
>>
>
>
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