[ic] mod_interchange and Apache MaxClients

Kevin Walsh kevin at cursor.biz
Thu Nov 17 15:33:50 EST 2005

I'm thinking about the PSP hanging issue and how that could effect things
and I'm lead to believe that the following is happening:

    1. User submits a request that causes a call to the PSP to be

    2. The PSP is taking its sweet time, so IC waits for a response.

    3. 10 seconds later, mod_interchange gives up and resubmits the
       user's request.  This compounds the problem.

    4. Loop back to #2 ten times, with a two second delay between

The above will probably wind up eating a lot of sockets, and also munch
its way through your processes leading to the problems reported.

I believe the following, posted earlier in this thread, is a symptom
of the later failures, rather than the initial cause:

> [Thu Nov 10 20:15:11 2005] [error] [client x.x.x.x] Malformed header
>  return by Interchange: 
> [Thu Nov 10 20:15:11 2005] [error] [client x.x.x.x] Premature end of
> script headers: /home/xxxxxx/public_html/favicon.ico

Can you check your logs to see if you can spot anything that looks like
"Failed to select the response header."

I could be wrong, but the above sounds plausible.

Possible workarounds, if you find the above error message.

    1. Upgrade Interchange.  Upgrade it now!  See the wget comments.

    1.1. Upgrade everything else while you're at it.  I see people are
       still using Red Hat 7 and Perl 5.6 for some reason.

    2. Add "ConnectTries 1" to the mod_interchange <Location>
       parameters in your Apache configuration.  This will cause the
       initial timeout to force a failure, rather than retry the request.

    3. Increase the mod_interchange timeout.  This can only be done by
       editing mod_interchange.c, to increase the IC_DEFAULT_TIMEOUT
       definition, and recompiling mod_interchange.so.  Perhaps I should
       make that configurable in the Apache config.

Give the above a try and see if any of it works.

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