RE: db_block_checking
Date: Fri, 29 Nov 2019 15:34:05 +0000
Message-ID: <13163_1575041663_5DE13A7F_13163_4079_1_b836ce91288e4752a8e108a2c3b41d35_at_vontobel.com>
Simply put, LOW calculates the checksum just for block headers, and MEDIUM for the whole data block content. So, "full semantic checks" in the documentation means "both headers and data".
This also explains why the performance with LOW doesn't depend on the block size (unlike MEDIUM and FULL, which is proportional to the block size): https://nenadnoveljic.com/blog/slow-dmls-with-larger-blocks/
Many thanks,
Nenad
-----Original Message-----
From: Mladen Gogala <gogala.mladen_at_gmail.com>
Sent: Freitag, 29. November 2019 16:21
To: Noveljic Nenad <nenad.noveljic_at_vontobel.com>; oracle-l_at_freelists.org
Subject: Re: db_block_checking
Hi Nenad!
That is described here:
Basically, LOW performs only the header validations. MEDIUM performs the full check (blood pressure, triglycerides, cholesterol, EKG) on all blocks except the index blocks. Full checks the index blocks as well. So, your assessment is correct: the worst that can happen with MEDIUM is to have a corrupt block written to your index, which would render it unusable.
Regards
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