key length

I would like to start a discussion about key length.

Cache Digests and Hint Caches both use md5 keys in
similarly central roles. However, Squid uses 16-byte digests and
Hint Cache uses 8-byte digests. Hint Caches distribute keys as part
of our updates, and so we are sensitive to key size, whereas Cache
Digests do not. We figured that that 64 bits is sufficient guard
against hash collisions, in a world that has less than 2^64 atoms.

Thoughts on a merge?

I could create two separate hash tables, with separate key-handling
code, to handle this (and suspect that's what's going to happen), but
it seems silly.

If we raise our size from 8 to 16 bytes, the current Hint protocol
structure rises from 20 to 28 bytes, raising per-update overhead 40%
and making the protocol that much less attractive in banwdwidth-scarce
spots.

Mike, I hope you don't mind that I cc'ed you, since I think
8 bytes was your decision originally.

-- 
Jon Kay        pushcache.com                      jkay@pushcache.com
http://www.pushcache.com/                             (512) 420-9025
Squid consulting				  'push done right.'