Re: 16-bit page checksums for 9.2

Alvaro Herrera <alvherre@commandprompt.com> writes:
> Excerpts from Robert Haas's message of jue mar 01 21:23:06 -0300 2012:
>> and that, further, you were arguing that we should not support
>> multiple page versions.

> I don't think we need to support multiple page versions, if multiple
> means > 2.

That's exactly the point here.  We clearly cannot support on-line
upgrade unless, somewhere along the line, we are willing to cope with
two page formats more or less concurrently.  What I don't want is for
that requirement to balloon to supporting N formats forever.  If we
do not have a mechanism that allows certifying that you have no
remaining pages of format N-1 before you upgrade to a server that
supports (only) versions N and N+1, then we're going to be in the
business of indefinite backwards compatibility instead.

I'm not entirely sure, but I think we may all be in violent agreement
about where this needs to end up.
        regards, tom lane