Re: [Mod-pubsub-developer] PHP push

[<kr...@po...>]

Derek Robinson writes:
> I wrote a proof-of-concept demo of 'Pushlets' in PHP a few months ago for
> my own amusement. I concluded (as did the Java Pushlets guy) that pushing
> content over http to more than 20 or so clients puts an unnecessarily big
> burden on the server. (In fact the Pushlet guy has been pushing 'pullets'
> for quite a while now.) 

Well, it depends.  Most web servers can handle ten hits a second
without any trouble; assuming 10 kilobytes per hit, 20 hits a second
saturates a T1.  If you have no inline images, and your users spend an
average of 60 seconds on each page, that's only 1200 users.  And if
you're trying to get out real-time updates to these folks by means of
"pull", you have a maximal latency of 60 seconds; if you want updates
to be twice as frequent, it takes twice the bandwidth and server load.

Now, by contrast, IRC servers on the Undernet regularly handle 20 000
clients.  When I first performance-tested the push_manager included in
mod_pubsub back in 2000, it could handle 4 000 simultaneous push
connections on a 1GHz box without any trouble, and that's on Linux
without any compile-time kernel tuning.  IRC servers generally run on
FreeBSD because its network stack scales better, or at least used to.

Typically, an IRC client sends a notification every 10-20 seconds, and
receives a message 1-10 times a second.

So, anyway, pushing out updates when they happen can impose a much
smaller load on the server's bandwidth than having the client poll in
common circumstances.

> But hey, if anyone's interested I could dig it out & dust it off ...

I'd love to see it.

-- 
<kr...@po...>       Kragen Sitaker     <http://www.pobox.com/~kragen/>
Edsger Wybe Dijkstra died in August of 2002.  The world has lost a great
man.  See http://advogato.org/person/raph/diary.html?start=252 and
http://www.kode-fu.com/geek/2002_08_04_archive.shtml for details.