Re: Restore and Recover Fuzzy datafiles

It seems, that Mark W. Farnham's reply didn't get into the list, so I'll quote his valuable response.

Probably, things have changed in some way at least starting from 9i. Now there is always an extra block at the beginning of each datafile (so called "zero" block) with some info about platform, actual file size etc, so the total file size is BLOCKS+1.

I've dumped the last block before and after "begin backup", with checkpoint and log switch - nothing was changed there and the datafile size was not changed either.

HTH

• Andrey

Mark W. Farnham wrote:
>
> All versions I'm aware of, though I haven't dumped the end of a 10g,
> and maybe not a 9i, either.
>
>
>
> If you create a datafile, you'll probably notice that the size on disk
> is at least 1 datablock size larger than you asked for. The very last
> OS set of blocks adding up to the database block size is the same as
> the very first one, except for a few key values that get
> resynchronized at checkpoints if I remember correctly. If I recall
> correctly one of the values in these blocks is also whether the
> tablespace was in backup. Prior to being able to lie to the database
> with a command and "end backup" (intended really not for copies of
> datafiles, but the current datafiles which cannot be block fractured
> in the case that the database crashes while in backup mode), you had
> to manually adjust that ending shadow end of the file block or Oracle
> would still know something was "wrong" with the file.
>
>
>
> This is also the reason why you have to make raw partitions a little
> bigger than the datafile you want to create there. I always thought it
> was funny (strange, odd sense of funny) that Oracle gave you one block
> less than the create size and took up one block more than the create size.
>
>
>
> If someone remembers the precise details of which programs update
> these blocks and under what conditions, and is free to disclose it,
> I'd enjoy reading that as well.
>
>
>
> In the case below, if DB writer is suspended for the split and the
> plex split operation generates a clean copy (note that that
> engineering detail is not necessarily required if the volume manager
> is only promising that the plexes remaining associated with the volume
> are identical, and there is possibly extra work flushing things at
> split time), then you're not going to have fracture blocks.
>
>
>
> You get fractured blocks when an OS utility copying OS sectors
> (usually 512 bytes) ends a particular read in the middle of an Oracle
> block and then the database writer writes the Oracle block before the
> next OS read starts.
>
>
>
>
>
> Regards,
>
>
>
> mwf
>
>
>
> -----Original Message-----
> *From:* oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org]*On Behalf Of *Andrey Kriushin
> *Sent:* Thursday, May 25, 2006 10:05 AM
> *To:* mwf_at_rsiz.com
> *Cc:* Oracle-L Freelists
> *Subject:* Re: Restore and Recover Fuzzy datafiles
>
>
>
>
> Never heard of "ending block". What version it was then? Mark, could
> you, please, clarify?
>

[skipped]
>
> TIA
>
> - Andrey
>
> Mark W. Farnham wrote:
>
> Before you could tell the database to "end" backup, you also had to
> patch the beginning and ending blocks of the file (lie to Oracle) so
> that Oracle did not consider the file to be "fuzzy," but I doubt
> you're working with a vintage of the Oracle software that old. If you
> are, you'll need some kind of binary block editor.
>

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