On Sat, Apr 13, 2013 at 06:14:28PM +0300, Ants Aasma wrote: > > CRCs are known to be good for that sort of thing; it's what they were > > designed for. I'd like to see some evidence that any substitute > > algorithm has similar properties. Without that, I'm going to vote > > against this idea. > > Sorry for creating confusion here by playing fast and loose with the > terminology. We are not talking about that hash function at all. What > we are talking about here is Fowler-Noll-Vo-ish > (http://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function) > hash function that is restructured to be parallelisable with SIMD > instructions with the explicit goal of being as fast as possible. The > resulting hash function is roughly two orders of magnitude faster than > 1-byte-at-a-time CRC32 currently in use. Performance is about > comparable with optimized fixed size memcpy running in cache. > > Based on current analysis, it is particularly good at detecting single > bit errors, as good at detecting burst errors as can be expected from > 16 bits and not horrible at detecting burst writes of zeroes. It is > quite bad at detecting multiple uncorrelated single bit errors and > extremely bad at detecting repeating patterns of errors in low order > bits. > > All in all I would say that the performance is worth the loss in > detection capability as we are not talking about using the checksum to > prove correctness.
Agreed. It would be good to get these details into the patch so others are not confused in the future. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
