Re: Block-level CRC checks

Andrew Chernow <ac@esilo.com> writes:
> I read through this patch and am curious why 0xdeadbeef was used as an 
> uninitialized value for the page crc.  Is this value somehow less likely 
> to have collisons than zero (or any other arbitrary value)?

Actually, because that's a favorite bit pattern for programs to fill
unused memory with, I'd venture that it has measurably HIGHER odds
of being bogus than any other bit pattern.  Consider the possibility
that a database page got overwritten with someone's core dump.

> Would it not be better to add a boolean bit or byte to inidcate the crc 
> state?

No, as noted that would give you a one-in-two chance of incorrectly
skipping the CRC check, not one-in-2^32 or so.  If we're going to allow
a silent skip of the CRC check then a special value of CRC is a good way
to do it ... just not this particular one.
        regards, tom lane