[mod_python] mod_python or apache scalability?

> Are you using mod_python sessions at all though?

No, we are not using sessions anywhere.

Alec.

> -----Original Message-----
> From: Graham Dumpleton [mailto:graham.dumpleton at gmail.com]
> Sent: Monday, October 01, 2007 4:00 PM
> To: Alec Matusis
> Cc: Jim Gallacher; mod_python at modpython.org
> Subject: Re: [mod_python] mod_python or apache scalability?
> 
> Are you using mod_python sessions at all though?
> 
> On 02/10/2007, Alec Matusis <matusis at matusis.com> wrote:
> > > Are you using Sessions, specifically DbmSession?
> > >
> > > Jim
> >
> > We are not using DbmSession
> >
> > Alec
> >
> > > -----Original Message-----
> > > From: Jim Gallacher [mailto:jpg at jgassociates.ca]
> > > Sent: Monday, October 01, 2007 4:55 AM
> > > To: Alec Matusis
> > > Cc: mod_python at modpython.org
> > > Subject: Re: [mod_python] mod_python or apache scalability?
> > >
> > > Are you using Sessions, specifically DbmSession?
> > >
> > > Jim
> > >
> > >
> > > Alec Matusis wrote:
> > > > I am sorry in advance if this turns out to be an apache-related
> > > issue, but
> > > > when I posted this on apache list, it has been suggested that it
> > > might be an
> > > > application issue, so I am reposting it here.
> > > >
> > > >
> > > > We are running a busy mod_python/3.1.4 Python/2.4.1 server on
> 2.6.9
> > > kernel,
> > > > that suddenly becomes very slow- requests either time out, or it
> > > takes
> > > > 10-20sec to serve a 1K thumbnail.
> > > > It is somewhat correlated with load spikes, but not perfectly (by
> > > looking at
> > > > the bandwidth graph, it never happens during the low bandwidth
> > > periods at
> > > > night, but it does not coincide with peaks of b/w)
> > > >
> > > > When we initially encountered an apache overload, it was always
> > > accompanied
> > > > with
> > > >
> > > > [error] server reached MaxClients setting, consider raising the
> > > MaxClients
> > > > setting
> > > >
> > > > in the apache error log. We also got
> > > >
> > > > kernel: possible SYN flooding on port 80. Sending cookies.
> > > >
> > > > in /var/log/messages system log.
> > > >
> > > > After that I raised MaxClients from 200 to 300. The problem
> initially
> > > > disappeared, but after our bandwidth grew a bit more, we got this
> > > behavior
> > > > again.
> > > > Now apache crashes (becomes very slow) silently, with no warning
> in
> > > apache
> > > > error logs at all (although we still get SYN flood message in the
> > > system
> > > > log)
> > > > When apache is this 'slow' regime, /server-status still shows
> > > available
> > > > slots, i.e. MaxClients is not reached.
> > > >
> > > > This is the relevant part of httpd.conf:
> > > >
> > > > ServerLimit 300
> > > > # we are using prefork MPM
> > > > StartServers 10
> > > > MinSpareServers 5
> > > > MaxSpareServers 20
> > > > MaxClients 300
> > > > MaxRequestsPerChild 10000
> > > > MaxMemFree 2500
> > > >
> > > > The server has 4GB of physical RAM and 4GB of swap. During these
> > > apache
> > > > "slowdowns", the swap size is still 0 and vmstat shows no
> swapping at
> > > all.
> > > > I suspect the problem may be in
> > > >
> > > > MaxMemFree 2500
> > > >
> > > > but then I would expect some kind of  "out of memory" errors in
> the
> > > logs?
> > > >
> > > > I am posting it on this list since I have not gotten a response
> in
> > > the users
> > > > list, and I think it's a bug for two reasons:
> > > >
> > > > 1) When apache is in this slow "degraded" regime, I would expect
> a
> > > log
> > > > message in the apache error log, with an explanation why.
> > > >
> > > > 3) If this is related to resource exhaustion, I would expect the
> > > server to
> > > > recover from this regime by itself when the load subsides, but
> this
> > > is not
> > > > the case. Only apachectl start/stop recovers the server.
> > > >
> > > >
> > > >
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> >
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