[mirror-admin] enabling keep-alives

[Axel Thimm]

We did have this discussion a year ago, and I think one also needs to
show the negative sides of keepalives. It isn't black or white
otherwise it wouldn't be an option.

On Wed, Apr 18, 2007 at 11:27:52PM +0200, Axel Thimm wrote:
> On Wed, Apr 18, 2007 at 03:46:48PM -0500, Matt Domsch wrote:
> > I'm working on the mirrormanager crawler, and have run across several
> > sites which offer content via http, but which don't have http
> > keepalives enabled.  Keepalives let downloads go much faster, as the
> > client doesn't have to establish a new TCP connection for every file
> > downloaded.
> 
> But note that keepalives are meant for speeding up small requests
> where setting up and tearing down the connection has a significant
> cost compared to the request's reply. For example a web site with many
> images. Or when yum did pull in the headers one by one (yum 2.0.x
> era).
> 
> Using it when downloading large chunks brings no real benefits, while
> there can be severe drawbacks: Keepalive keeps the slots open for a
> given time even when the client has stopped downloading, so you get
> more processes doing nothing compared to non-keepalive. This may make
> load and memory explode, if this is a busy mirror. And indeed my
> mirrors using keepalive sometimes go to valhalla when there is an FC
> release, and I need to turn keepalive off during the storm.
> 
> > Both end users with yum, and mirrormanager's crawler, will be much
> > happier if you can enable keepalives.
> 
> crawler yes, but yum probably not, since yum doesn't pull in little
> chunks anymore, but rather big *.xml.gz or *.rpm bits.
> 
> Just a warning that keepalive is not always a blessing, and needs to
> be evaluated on a per mirror basis by the mirror admin.

-- 
Axel.Thimm at ATrpms.net
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