Hiyas Steve, Steve Snyder wrote:
What do the new epoll and COSS options offer to me as the administrator of a lightly-loaded Squid server? Anything?
On a "lightly-loaded" server, not much. It will help scale the use of this server (giving the possibility of handling more users with the same hardware). If this is not an issue for you, there's no need to worry right now.
I usually read of epoll in the context of being recommended for a Squid server with very high CPU utilization. I'm not clear on the advantages of COSS over other disk storage schemes.
Unix daemons (squid included) usually calls poll() or select() to handle file descriptors. Specifically to squid, it will mean how much users your machine is able to handle.
The use of poll() by itself is not a problem. It starts to be a an issue when your process (squid) needs to handle hundreds of file descritors at the same time, as it will use more and more processor time.
In the other hand, epoll() is a newer interface to handle file descriptors (specific to Linux, using kernel 2.6). It is way smarter then poll() or select(), as it uses less resources then both syscalls, and scales better. Processes using epoll() will be able to open more FDs at the same time (using less processor power for that), when comparing to poll() or select().
Surelly Chad (or someone else) will correct me if I'm wrong, but COSS is a different aproach to storing objects on a disk cache. It is not just meant to be "faster" then ufs, aufs or diskd, but, "smarter". Basically talking, it tries to create a "raw device" (be it a real disk partition or a simple file), and store all cache objects on this device. Objects will then be stored/retrieved in a faster/lighter/smarter way then other cache mechanisms.
Unfortunatelly, COSS is not quite stable as ufs/aufs/diskd. And if I'm not wrong, is not recommended for production use (yet). Of course, the squid developers will be really glad to find another beta tester for this item.
I am currently using UFS on a single ReiserFS-formatted cache, on Linux. This setup is working fine, but I am always looking for improvement. (Given that I do not suffer from high CPU use, improvement would be defined as reduced latency in cache look-ups.) Any thoughts on what these new option might mean for a lightly-loaded server?
If I was you, I would use squid 2.6stable2, reiserfs (with the options "noatime,notail"), and "aufs" as the storage system. Also, if you're using kernel 2.6 on your linux machine, epoll() would be a fine option to use too.
COSS would be real fine for a devel or test machine, or if you feel the need to help testing (and mature) it.
Thanks.
Regards, Domingos. -- Domingos Parra Novo Coordenador de Projetos Terra Networks Brasil S/A Tel: +55(51)3284-4275
