Summary: Web Server Performance
Jeff Mogul provided just the right information. There is an
easy fix for DEC UNIX 3.2C and the Web page he refers to is
impressive. Thanks, Jeff.
Jim Skoog
From: mogul_at_pa.dec.com (Jeffrey Mogul)
Newsgroups: comp.unix.osf.osf1
Subject: Re: Web Site Performance
Date: 30 May 1996 00:50:25 GMT
Organization: DEC Western Research
In article <skoogDs54BH.9pF_at_netcom.com> skoog_at_netcom.com (Jim Skoog) writes:
>Where are the performance bottlenecks for Alpha AXP running the
>Netscape Commerce Server 1.12 with high volume internet traffic?
>We are evaluating network performance for a variety of Alpha AXP
>runing DEC UNIX 3.2C, which run DEC's seal firewall and behind
>that Alpha 1000 and 2100 webservers.
Our experience (running such Web servers as altavista.digital.com
and www.digital.com) is that there is one important kernel tuning
knob to adjust in order to get good performance on V3.2C. You
need to patch the kernel global variable "somaxconn" (use dbx -k
to do this) from its default value of 8 to something much larger.
How much larger? Well, no larger than 32767 (decimal). And
probably no less than about 2048, if you have a really high volume
(millions of hits per day), like AltaVista does.
This change allows the system to maintain more than 8 TCP
connections in the SYN_RCVD state for the HTTP server. (You
can use "netstat -An |grep SYN_RCVD" to see how many such
connections exist at any given instant).
If you don't make this change, you might find that as the load gets
high, some connection attempts take a very long time. And if a lot
of your clients disconnect from the Internet during the process of
TCP connection establishment (this happens a lot with dialup
users), these "embryonic" connections might tie up your somaxconn
quota of SYN_RCVD-state connections. Until the kernel times out
these embryonic connections, no other connections will be accepted,
and it will appear as if the server has died.
The default value for somaxconn in Digital UNIX V4.0 will be quite
a bit larger than it has been in previous versions (we inherited
this default from 4.3BSD).
Digital UNIX V4.0 includes some other performance-related changes
that significantly improve its maximum HTTP connection rate. However,
we've been using V3.2C systems to front-end for altavista.digital.com
with no obvious performance bottlenecks at the millions-of-hits-per-day
level.
We have some Webstone performance results available at
http://www.digital.com/info/alphaserver/news/webff.html
I'm not sure if these were done using V4.0 or an earlier version
of Digital UNIX, although I suspect they were done using a test
version of V4.0.
-Jeff
Received on Fri May 31 1996 - 01:35:22 NZST