Re: Block-level CRC checks

Aidan Van Dyk <aidan@highrise.ca> writes:

>> Wal logged changes are safe because of full_page_writes. Hint bits are  
>> safe because either the old or the new value will be on disk and we  
>> don't care which. It doesn't matter if some hint bits are set and some  
>> aren't.
>> 
>> However the checksum won't match because the checksum will have been  
>> calculated on the whole block and part of it was never written.
>
> Correct.  But now doesn't full-page-writes give us the same protection
> here against a half-write as it did for the previous case?
>
> On recovery after a torn-page write, won't the recovery of the
> full_page_write WAL + WAL changes get us back to the page as it was
> before the buffer+checksum+write?  

Hint bit setting doesn't trigger a WAL record.

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