I'm using a slightly modified FNV hash in my client (http://
codeplex.com/EnyimMemcached), taken from here: http://
bretm.home.comcast.net/hash/6.html
The site has a good evaluation of common hash functions, good read.
a.
On Aug 30, 2007, at 1:32 PM, Mikael Johansson wrote:
Hi,
My vote is on using Brad's implementation but switch from SHA1 to
CRC32 for
simplicity's sake and to get a nice 32bit hash, MD5 is slow and
generates a long
digest of which we only need the first bytes.
Richard Jones wrote that he would compare the CRC32 to FNV with
regards to
distribution and speed. If FNV would indeed be a better/faster
choice I'd propose
to use FNV-1a to generate 32bit hashes using the FNV_prime and
offset_basis from
http://isthe.com/chongo/tech/comp/fnv/
"Some people use FNV-1a instead of FNV-1 because they see slightly
better
dispersion for tiny (<4 octets) chunks of memory." -
i.e. short keys
An argument for using CRC32 over FNV could be that many script
languages ship
with a native CRC32 implementation, so it'd easier and result in
higher
performance for folk who writes clients in these languages.
//Mikael
On Thu Aug 30 10:48 , dormando sent:
A couple, I think ;)
Mikael, I think now's as good of a time as ever to decide on the
hashing
standard. Believe brad's asked a few times if anyone has any
complaints
with the Perl version, or any reasons/preferences as to one
implementation or the other. There's no authority on this other
than the
people who respond here and have compelling arguments :)
I only know of (offhand):
- Yours
- libketama
- Set::ConsistentHash
... maybe Dustin wrote one? Maybe apr_memcache has one? I forget.
All that really matters is that an approach not everyone completely
absolutely hates is decided on, so this can get into use. Based on
MD5?
Based on CRC32? What works best?
-Dormando
Mikael Johansson wrote:
Hi,
I believe there's already people using consistent hashing on large
installs out there. As to the pecl/memcache client the code is not
released and still in CVS, but it is stable (and certainly ready
to be
evaluated/tested), also a release is coming up so you can either
wait
for that or build from source like
cvs -d :pserver:[EMAIL PROTECTED]:/repository checkout pecl/
memcache
cd pecl/memcache
phpize
./configure
make && make install
Enable it by setting an php.ini entry like
memcache.hash_strategy = consistent
Please note that the consistent hashing implementation might still
change in the future when a standard is reached on the subject.
//Mikael
Ajinkya Nahar wrote:
Hi all,
I want to know whether consistent hashing technique can be used in
production environment.
Is it still too young or is it of production quality?
Also, what configuration needs to be done in the PHP client when
using
consistent hashing?
Please let me know.
Thanks in advance.
Regards,
Ajinkya
)
