On Wed, 2010-12-22 at 10:45 -0500, Tom Lane wrote:
> Aidan Van Dyk <aidan@highrise.ca> writes:
> > With this statement, you just moved the goal posts on the checksumming
> > ideas. In fact, you didn't just move the goal posts, you picked the
> > ball up and teleported it to another stadium.
>
> What he said. I can't imagine that anyone will be interested in any
> case other than "set the CRC immediately before writing, and check it
> upon first reading the page in". Maintaining it continuously while the
> page is in shared memory is completely insane from a cost-versus-benefit
> perspective.
If you insist on setting hint-bits, then that is probably true.
Many people experience almost no I/O these days, and there's a strong
correlation between people caring about their data and also being
willing to spend big $s on cache. We need to protect our users, however
much money they spent on cache; I would argue the more money they spent
on cache the harder we should be trying to protect them.
I'm sure it will take a little while for everybody to understand why a
full CRC implementation is both necessary and now possible. Paradigm
shifts of thought do seem like teleports, but they can be beneficial.
-- Simon Riggs http://www.2ndQuadrant.com/books/PostgreSQL Development, 24x7 Support, Training and Services