Re: 16-bit page checksums for 9.2

On Mon, Feb 20, 2012 at 6:22 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Mon, Feb 20, 2012 at 12:53 PM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
>> On 2/20/12 5:57 AM, Robert Haas wrote:
>>> 3. You're rearranging the page header in a way that I find ugly and baroque.
>>
>> Guys, are we talking about an on-disk format change?  If so, this may
>> need to be kicked out of 9.2 ...
>
> Yes, we are.  Simon's gone to some pains to make it backward
> compatible, but IMHO it's a lot messier and less future-proof than it
> could be with some more work, and if we commit this patch than we WILL
> be stuck with this for a very long time.

No, we aren't. The format is not changed, though there are 3 new bits added.

The format is designed to be extensible and we have room for 10 more
bits, which allows 1024 new page formats, which at current usage rate
should last us for approximately 5000 years of further development.
Previously, we were limited to 251 more page formats, so this new
mechanism is more future proof than the last. Alternatively you might
say that we have dropped from 1271 page formats to only 1024, which is
hardly limiting.

This has already been discussed and includes points made by Bruce and
Heikki in the final design. The "more work" required is not described
clearly, nor has anyone but RH requested it. In terms of messier, RH's
only alternate suggestion is to split the checksum into multiple
pieces, which I don't think yer average reader would call less ugly,
less messy or more future proof.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
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