Re: Protecting against unexpected zero-pages: proposal

On Mon, Nov 8, 2010 at 12:53 PM, Greg Stark <gsstark(at)mit(dot)edu> wrote:
> On Mon, Nov 8, 2010 at 5:00 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> So maybe Aidan's got a good idea here.  It would sure be a lot easier
>> to shoehorn checksum checking in as an optional feature if the checksums
>> were kept someplace else.
>
> Would it? I thought the only problem was the hint bits being set
> behind the checksummers back. That'll still happen even if it's
> written to a different place.

The problem that putting checksums in a different place solves is the
page layout (binary upgrade) problem. You're still doing to need to
"buffer" the page as you calculate the checksum and write it out.
buffering that page is absolutely necessary no mater where you put the
checksum, unless you've got an exclusive lock that blocks even hint
updates on the page.

But if we can start using forks to put "other data", that means that
keeping the page layouts is easier, and thus binary upgrades are much
more feasible.

At least, that was my thought WRT checksums being out-of-page.

a.

--
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