Re: Block-level CRC checks

On Thu, Oct 2, 2008 at 7:42 PM, Jonah H. Harris <jonah(dot)harris(at)gmail(dot)com> wrote:
>> It's not the buffeting it's the checksum. The problem arises if a page is
>> read in but no wal logged modifications are done against it. If a hint bit
>> is modified it won't be wal logged but the page is marked dirty.
>
> Ahhhhh. Thanks Greg. Let me look into this a bit before I respond :)

Hmm, how about, when reading a page:

read the page
if checksum mismatch {
flip the hint bits [1]
if checksum mismatch {
ERROR
} else {
emit a warning, 'found a torn page'
}
}

...that is assuming we know which bit to flip
and that we accept the check will be a bit
weaker. :) OTOH this shouldn't happen too
often, so performance should matter much.

My 0.02

Best regards,
Dawid Kuroczko

[1]: Of course it would be more efficient to flip
the checksum, but it would be tricky. :)
--
.................. ``The essence of real creativity is a certain
: *Dawid Kuroczko* : playfulness, a flitting from idea to idea
: qnex42(at)gmail(dot)com : without getting bogged down by fixated demands.''
`..................' Sherkaner Underhill, A Deepness in the Sky, V. Vinge