RE: db_block_checking

From: Noveljic Nenad <nenad.noveljic_at_vontobel.com>
Date: Fri, 29 Nov 2019 14:52:28 +0000
Message-ID: <9259_1575039170_5DE130C2_9259_2308_1_8c95905e6207475fa60c470f22507f28_at_vontobel.com>

Thanks, Mladen.

Yes, DB_BLOCK_CHECKING verifies the structure in memory. It's also worth mentioning that this happens with each DML. As you mentioned, the block isn't written and reread for verification purposes.

Would you happen to know the difference between LOW and MEDIUM?

So, with DB_BLOCK_CHECKING=MEDIUM the worst that can happen is that a corrupt index block gets written to disk? In other words, there's a possibility of a downtime between detecting this problem and rebuilding the index.

Best regards,

Nenad

https://nenadnoveljic.com/blog/

-----Original Message-----
From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of Mladen Gogala Sent: Freitag, 29. November 2019 15:21
To: oracle-l_at_freelists.org
Subject: 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

---

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†Ûiÿü0ÁúÞzX¬¶Ê+ƒün– {ú+iÉ^ Received on Fri Nov 29 2019 - 15:52:28 CET