db_block_checking
Date: Fri, 29 Nov 2019 09:49:58 +0000
Message-ID: <27382_1575021007_5DE0E9CF_27382_8324_1_614a3a2698c84359825d895af20a2965_at_vontobel.com>
I've been always setting db_block_checking to FULL(TRUE). However, it wasn't until recently, that I measured a significant impact on DML performance when db_block_checking is set to MEDIUM or FULL. Further, this degradation is clearly more severe with larger block sizes.
This prompted me to think of other options. Now, I need your help in understanding the risks associated with different settings.
First of all, I don't want to use OFF - for obvious reasons.
Second, the difference between LOW and MEDIUM are "full semantic checks", see Oracle documentation https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/DB_BLOCK_CHECKING.html#GUID-23700E5C-6BFC-48C2-9728-EB1F93F95DD6 .
What are these "full semantic checks" and what would be the risk of omitting them (i.e., setting db_block_checking to LOW)?
Finally, the only difference between MEDIUM and FULL - according to the documentation - is that the aforementioned "full semantic checks" aren't performed for the index blocks. A little side note, though: I measured a significant DML performance difference between MEDIUM and FULL even on non-indexed tables.
What do you think could happen in case of an unnoticed index block corruption (that is, with MEDIUM)? Wrong results or some ORA-0600/ORA-07445, perhaps?
If you're using anything less than FULL, could you explain your decision?
Best regards,
Nenad
https://nenadnoveljic.com/blog/
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-- http://www.freelists.org/webpage/oracle-lReceived on Fri Nov 29 2019 - 10:49:58 CET