Re: CRC checks WAS: How much do the hint bits help?

> I believe that most of the people talking about and wanting checksums
> so far have been wanting them to verify I/O, not to verify that PG has
> no bugs, that RAM is staying charged correctly, and that no stray bits
> have been flipped, and that nobody else happens to be scribbling over
> our shared buffers.

I agree that this should be our first goal. Yes, we want to protect
users against memory errors as well. However, that's a much tougher
feature to implement; I've done some hashing this out with engineers on
other DBMSes and nobody has good answers right now. The overhead of
what Simon proposes would be enormous, and few users would be interested
in paying that cost.

Doing a CRC check-on-write, as well as checking for format corruption
before write would catch a majority of real-world problems. Please
don't hold that up in pursuit of the bit-flipping problem, which
*nobody* has solved.

--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com