Re: db_block_checking

Hi Nenad!

DB_BLOCK_CHECKING is a syntax check only which verifies the block structure in memory. It's different from DB_BLOCK_CHECKSUM, which writes the full checksums into block header. To my knowledge, Oracle doesn't do the write verification with re-reading the block back to memory and recomputing the checksum because of fairly dramatic performance impact. I usually do DB_BLOCK_CHECKING on medium, unless the database is so critical that I cannot afford to rebuild indexes.

Regards

On 11/29/19 5:08 AM, Noveljic Nenad wrote:
> Thanks, Stefan.
>
> The article discusses the problem of switching it off completely, that is, compares he default block tail mechanism with check summing in general. It, however, doesn't deal with differences between LOW and MEDIUM.
>
> Best regards,
>
> Nenad
>
> https://nenadnoveljic.com/blog/
>
>
> -----Original Message-----
> From: Stefan Koehler <contact_at_soocs.de>
> Sent: Freitag, 29. November 2019 11:00
> To: Noveljic Nenad <nenad.noveljic_at_vontobel.com>; ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org>
> Subject: Re: db_block_checking
>
> Hello Nenad,
> I think David Loinaz ( https://twitter.com/DavidLoinaz ) or Gabriel Alonso ( https://twitter.com/Gaalons0 ) are the go-to-guys for this question as they deal / dealt with this kind of stuff all day :)
>
> David has also written a more general blog post about it here but not particular to your question about LOW / MEDIUM: https://davidloinaz.wordpress.com/2016/02/24/db_block_checksum-and-risk-perception/
>
> Best Regards
> Stefan Koehler
>
> Independent Oracle performance consultant and researcher
> Website: http://www.soocs.de
> Twitter: _at_OracleSK
>
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