[Pan-users] Re: Inefficiencies in Pan threading?

[Duncan]

Calin A. Culianu posted
<address@hidden>,
excerpted below,  on Sun, 14 Sep 2003 01:21:25 -0400:

> I am still a little puzzled by the sporadic delays and stalls I get while
> downloading from my news server.  I previously thought this was dead time
> Pan was spending decoding downloaded chunks, but perhaps it is caused by
> something else outside of Pan (such as the news server itself).  From your
> description it sounds like Pan may not be the source of the delay -- it is
> after all trying to minimize "dead time" by interleaving downloading with
> decoding.. is this a correct assessment?
> 
> Would you have any insights into how I can prevent the stalling I am
> seeing?  Or should I look outside of Pan altogether to solve the problem
> (like maybe my news server is being slow sporadically..)?

As you mention, that addresses the threading issues, but doesn't do
anything for the idle time issues.  When I've seen that, which isn't
often, it has been due to stale "dead" connections that the server still
thinks I'm using, because they didn't get closed properly, for whatever
reason.  Three questions..

Are you sure your news provider allows you four connections to the server?
Obviously, if not, and you have PAN configured for four, it's going to
cause problems when PAN keeps trying to get more connections than the
server will allow.

What are your caps like, both on your overall pipe, and on each
connection?  If you have dialup or a low bandwidth DSL, and the
connection caps are high enough, only one or two full connections may fill
your available bandwidth, meaning you are not using your available
bandwidth to best efficiency in the best case, and possibly causing
connections to starve and be dropped as idle.  If that's happening, and
the pipe is already full, the connection termination may not be able to
get thru properly and the server may think the old connections are still
active.  If these stale connections fill up your quota, then PAN won't
have any choice but to keep waiting and trying, until one of them times
out, and it can connect again.

In either of the above cases, dropping your number of connections to
something more in line with the resources available may actually improve
your throughput, eliminating most of the idle time.  Since PAN tends to be
fairly efficient using the connections available, it's possible you need
fewer connections to fill your pipe to capacity than might have been
needed with another news client.

What is your connection quality?  Do you have any problems with dropped
packets?  Does your ping time to the general internet or that server in
particular have large swings?  (Try installing the program "MTR", "Matt's
TraceRoute", if you don't have it installed already, and see what it says
the connection is like.  It's an invaluable tool for checking out route
stability.)  If the connection quality isn't the best, it could be
connections dieing on the vine, so to speak, due to ACKs being dropped
somewhere along the line.  This will exacerbate the problems above if you
have them as well, as some of the connection maintenance messages just
won't make it thru, causing even MORE problems.  This can be quite common
on dialup, as its reliance on analog isn't an ideal solution anyway, and
even the slow connections dialup has are made worse by the unreliability
in far to many cases.  On broadband, assuming you aren't having
the always possible physical connection issues, the problem is often
overloaded routers or pipe segments somewhere between you and the server
in question.  This can be at the gateway hop, others under control of your
ISP, or further out on the internet backbone, if your news provider isn't
located on all-private network from you.  Unfortunately, lowering the
connection count or pretty much anything else you may do doesn't have a
lot of effect here, except for switching providers, either ISP or NSP,
depending on where the problem is, to something more reliable.

BTW, this belongs on the user list, not the devel list, as it's not a
devel issue.  It was possible it might BECOME a development issue, from
your standpoint, if PAN indeed DID have bad threading or whatever, but
unless you KNOW that's the case and have a proposed solution, the user
list is the appropriate place for the post.  Not that it matters a /whole/
lot as the developers are normally active in both, but it /does/ help to
keep things more organized if posts are kept on topic for the list in
question, meaning user for anything that isn't known to be specifically
development related.  Just a friendly reminder for next time, OK?

-- 
Duncan - List replies preferred.   No HTML msgs.
"They that can give up essential liberty to obtain a little
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Benjamin Franklin