Re: Cost of XLogInsert CRC calculations

"Mark Cave-Ayland" <m.cave-ayland@webbased.co.uk> writes:
> Wow, a 64-bit CRC does seem excessive, especially when going back to Zmodem
> days where a 50-100k file seemed to be easily protected by a 32-bit CRC. I'm
> sure there are some error rates somewhere dependent upon the polynomial and
> the types of error detected.... Try the following link towards the bottom:
> http://www.ee.unb.ca/tervo/ee4253/crc.htm for some theory on detection rates
> vs. CRC size.

When the CRC size was decided, I recall someone arguing that it would
really make a difference to have 1-in-2^64 chance of failure rather than
1-in-2^32.  I was dubious about this at the time, but didn't have any
evidence showing that we shouldn't go for 64.  I suppose we ought to try
the same example with a 32-bit CRC and see how much it helps.

			regards, tom lane