sbwait state for loaded Apache server

From: Michael Conlen (meconlen_at_obfuscated.net)
Date: 07/22/03

  • Next message: Simon J Mudd: "Re: Tuning for PostGreSQL Database" 
    Date: Tue, 22 Jul 2003 12:49:08 -0400
To: freebsd-performance@freebsd.org

    I'm working with an Apache webserver running 1400 apache processes and
    the system pusing somewhere in the area of 50-60Mbit/sec sustained. The
    system seems to top out around 60Mbit/sec and I see some minor
    degradation of server response times. The server response times are
    generally very very stable otherwise. Most of the apache processes are
    in the sbwait state. I've got 4Gig of memory, so I can play with some of
    the values (nmbclusters has been turned up and I never see delayed or
    dropped requests for mbufs).

    I don't see in my old Design & Implementation of 4.4BSD (Red Book?) much
    about the state, and I don't a copy of TCP/IP Illustrated 2 handy these
    days, but if memory serves sbwait is waiting on a socket buffer
    resource. My guess is that these are processes waiting on the send
    buffer to drain.

    $ netstat -an | egrep '[0-9] 3[0-9]{4}' | wc -l
         297

    seems to indicate that I've got a lot of processes waiting to drain.
    Looking at the actual output it shows most of these are ESTABLISHED.

    So my thought is by increasing the send queue size I could reduce this.
    I've got a pretty good idea on the size of the files being sent and my
    thoughts were to increase the send-q size to where Apache can write()
    the file and go to the keep alive state quickly instead of waiting. So
    the questions are

    Would this affect actual network performance
    Would this reduce load on the machine (a handy thing to do, but secondary)
    given c = number of connections and q = queue adjustment and s = size of
    mbuf do I just need to make sure I have (c*q)/s buffers available, and
    any fudge?
    How do I know when I need to increase the overall system buffer size
    beyond 200 MB? 

    --
Michael Conlen
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  • Next message: Simon J Mudd: "Re: Tuning for PostGreSQL Database"