[mod_python] requests are blocking when using req.sendfile

Graham Dumpleton graham.dumpleton at gmail.com
Tue Sep 23 21:19:15 EDT 2008

2008/9/23 Matt Barnicle <mattb at wageslavery.org>:
> i'm having an issue with our site, which seems to be directly
> related to using req.sendfile.  on our site, we have secure music
> downloads.  the user has to go through a series of steps in order to
> gain access to the music (fyi, we run a legitimate service, not a
> pirate or warez site).  just some background info..  basically we
> can't offer a direct download link or the security can be bypassed.
> so downloading is done through the handler, which runs the checks,
> and if everything looks good, the file is sent to the browser using
> req.sendfile with the local path to the file on disk.
> it works..  but the problem is, requests start backing up whenever a
> download is being sent.  it looks like new requests are being sent
> to the apache process that is tied up sending the download file.  i
> don't understand why this is happening though.  i would think that
> while it's sending the file, no new requests would be queued in that
> process.  i can verify this easily by downloading a file, and while
> it's downloading, clicking on a link on the site from the same
> window in which i downloaded in.  the request will stay in the WAIT
> state (according to mod_status) until the download is finished, then
> the page will load and the queue will clear up.  now if i change the
> download link to a static file, served directly by apache, this
> problem disappears.
> what can i do to fix this?  it's a major issue right now.  many
> times a day you can go to the site and it will hang for perhaps 1 to
> 3 minutes, then it will load, due to the above described situation.
> version notes:
> CentOS release 5 (Final)
> apache 2.2.3
> mod_python 3.2
> using prefork compiled into apache.  misc apache configuration:
> KeepAlive Off
> <IfModule prefork.c>
>  StartServers       8
>  MinSpareServers    5
>  MaxSpareServers   20
>  ServerLimit      256
>  MaxClients       256
>  MaxRequestsPerChild  4000
> </IfModule>
> thank you for your time and consideration..

Are you setting a content length on the response before calling req.sendfile()?

How many concurrent requests for these files are you receiving and how
long does it take to download a file?



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