It uses a consistent hashing library that the guys from last.fm
released a week or two ago so hashes should stay the same. If a
server fails while the program is executing it should mark it as dead
and stop using it but I haven't tested this very well. However there
is no way to mark a server as dead currently so it will continue to
attempt connections on every new page due to some restrictions in
libketama which I need to fix :)
Alex Stapleton
[EMAIL PROTECTED]
T: 0207 0700 956
On 29 Apr 2007, at 05:04, Don MacAskill wrote:
Very cool. Can't wait to take a look.
Does your library support the idea of server state? In other
words, if a server crashes or is otherwise marked offline (but is
planned to return, so not removed from the list), does the hashing
still stay consistent?
Ideally, we don't want items to get re-hashed to a new server
(unless, of course, the server is permanently removed from the
pool) because then there's the chance for stale cache reads in the
future. Instead, we want the hashing to take the same # of servers
into account, but for the client to simply not attempt reads/writes
to servers marked "down".
The PECL extension added similar functionality in 2.1.0, and I
believe it's fairly common practice.
Alex Stapleton wrote:
Well I mentioned I had written a UDP capable C library for working
with memcached a couple of days ago and here it is. It requires
libketama, libevent and uses Boost.Build currently. Included is a
PHP library that provides access to it, and pretty much zero
documentation. There is a fairly comprehensive example program and
a test PHP script as well. It works pretty well but has not been
tested in any sort of failure scenario yet.
libevent: http://www.monkey.org/~provos/libevent/
libketama: http://www.last.fm/user/RJ/journal/2007/04/10/392555/
Here's the README with more info
=======
cmemcache - C memcached client
authors: Alex Stapleton <[EMAIL PROTECTED]>
version: 0.5 - Dedicated to Varablese, the Greek God of
uncertainty.
date: 28 Apr 2007
This is the first revision of this client, it seems to mostly work
and valgrind
doesn't report any massive memory issues with it. *crosses
fingers* This is
probably usable. It supports TCP and UDP and relies on libketama,
libevent and
Bost.Build. Links to dependencies are down below. Currently it is
assumed all
servers are operating in both UDP and TCP mode with the UDP port 1
higher than
the TCP port listed in the ketama server file. This is a lame hack
I know.
It should be pretty easy to add support to force a server to only
do TCP though.
The PHP module has been tested under PHP4 and PHP5. This extension
has not
been used in a high load situation yet. Proper QA and bugfixing
has not
been done. This is going to be happening over the next week or two
as we
roll it out onto our web servers.
Get requests are sent aynchronously using libevent which means you
get pretty
good performance using large numbers of servers for batch requests.
I am almost certain there are horrendously evil bugs in this code.
If anything
breaks and loses your customers or sets your parents on fire, it's
not my fault.
=======
You can only get it from SVN right now the repo is at
svn checkout http://cmemcache.googlecode.com/svn/trunk/ cmemcache
Just type bjam to build it (assuming you have Boost.Build v2
installed.)
I'd appreciate any feedback (especially in the form of patches ;)
no matter how scathing.
Alex Stapleton
[EMAIL PROTECTED]
