[Pan-users] Re: Weird cache problem

[Jim Henderson]

On Sat, 29 Aug 2009 03:31:16 +0000, Duncan wrote:

> I've seen absolutely nothing like that here, multiple servers, but not
> multiple authenticated ones (one authenticated, some time ago, none for
> awhile tho).

Good to know.  I actually have a total of 4 servers plus one dummy 
(0.0.0.0 - which I use for my default posting profile so I don't 
accidentally post to a group with a bad profile - had that happen too 
many times).

There is actually another weird piece to this that I had forgotten about, 
and that's that occasionally when posting a reply, I'll get a "no such 
group:  <group.goes.here>" when posting a reply.  The dumb thing is that 
the group, while hosted on the server I'm posting to, isn't actually the 
group I'm posting to; it's nowhere in my headers.  So I might be posting 
to, say, opensuse.org.help.install-boot-login and when I post, I get a 
message saying "no such group:  novell.community.chat".  Now o.o.h.i is 
hosted on the same server as n.c.c.  Both groups are actually hosted on 
both servers (forums.novell.com and forums.opensuse.com - they're 
actually the same server with two different DNS addresses).  I recently 
became a moderator on forums.opensuse.org so I use a set of login 
credentials to access some private groups.  I also use a different set of 
credentials on forums.novell.com.

And to really confuse things, I read the forums.opensuse.org groups using 
the forums.novell.com address, but when I got the new credentials, I 
switched servers (to make it easier to deal with the authentication).

Both of the groups above are public groups - accessible with or without 
authentication.

Come to think, there is a third oddity that I just realized was new - 
occasionally when hitting groups on forums.opensuse.org, a group's 
headers will completely redownload, and old messages (that haven't 
expired) will show up as unread.

> Two observations:
> 
> One:  I /have/ seen occasional problems with posts that show no bodies
> at all.  From my troubleshooting, this almost always involves posts with
> some exotic non-ASCII character, say a UTF-8 no-wrap-blank-space (IDR
> for sure what the technical term for them is ATM, is that correct?, I
> just woke up and my mind is still coming back up to speed) or the like.

I see this from time to time, in two different forms.  If I see that the 
article is cached and I can't see anything, I toggle quoting - one state 
it shows, one state it doesn't.

If it isn't cached (as occasionally happens when reading this list or 
others through gmane), if I read a few messages (or I've found, just hit 
"enter" repeatedly on the message), eventually it'll download and I'll 
see it.

> But I don't see how that's directly connected to the behavior you're
> seeing.  It just came to my mind as a similar oddity.  

Yeah, this is something different - but it is a similar oddity.

> It is possible
> that it's that oddity triggering it, but with different results due to
> some other oddity, or if you're on 32-bit, maybe it's the same oddity
> expressed in 32-bit where mine is 64-bit (x86_64 aka amd64).

I'm actually on x86_64 here as well.

> Two: About how pan's cache works:  Pan saves the actual messages using
> the message-ID as the filename, translating filesystem-invalid
> characters where necessary.  It's thus possible to troubleshoot if you
> can figure out the message-ID (say from the attribution of a reply, or
> by grepping the cache for a file containing the subject, author, group,
> etc.

Hmmm, that's a good idea.  I'll give that a try - I usually can see a 
reply to the problem message (in fact, so far, I think I always have been 
able to open other messages and read them without a problem).

> If you save the message text, pan uses the same message-id for saving
> that, possibly just copying the cache file to wherever you save the
> message, possibly copying the message as in pan's own memory buffer but
> using the same message-id as a filename.  It could be worthwhile to try
> that with both the original "duplicated" message, and the
> fake-duplicate, when you see the problem, as an initial troubleshooting
> measure.

The weird thing is that if I restart the problem goes away for a while - 
it's not reproducible with a specific message.  But next time I see it 
happen, I'll have a look at the cache directory.

> Meanwhile, it seems to me the problem must be that for some reason, pan
> isn't updating its message-ID pointer when you change messages, so you
> see the same one, instead of the new one.  There must be some code path
> without that critical update, or perhaps more likely, with a race
> condition between two threads.  (Most of pan is single-threaded, but
> worker threads are hatched in certain cases, generally where there was
> an observed bottleneck.)

The really odd thing is that this didn't ever happen until I changed that 
authentication setting.  There seems to be a correlation.

> Which brings up the question in regard to threading:  How many
> connections do you have running to each of the servers concurrently, and
> how many CPU cores is your machine?  For the programmers out there (I
> speak and understand the lingo and concepts to some degree, but don't
> claim to be a programmer), it should be clear where I'm going with this.
> Multiple threads, multiple cores processing them, very good recipe for
> thread-races if the code isn't 100% concurrent-multi-entrant.

2 core system, 4 connections per server.

With the total of three oddities now, I'm wondering if I ought to wipe 
the config and start over and see if the problem persists.  Maybe 
something in my config is borked.

Jim
-- 
 Jim Henderson
 Please keep on-topic replies on the list so everyone benefits