Subject: odd load patterns

From: Miles Fidelman <[email-masked]>
Date: Tue, 13 Sep 2016 20:09:26 -0400

Hi,

I wonder if anybody might have some thoughts on this:

Lately, our server has been showing high loading, but top shows that the 
CPU is mostly in wait mode, and iotop shows low disk i/o traffic.

Usually, the system shows high load when either

a. Someone is indexing our web server (which shows up as CPU load on 
apache).

b. Our list manager is processing a bunch of traffic (most of the load 
comes from spam and virus filtering - which shows up as cpu load on 
amavisd, and clamd, as well as a lot of disk i/o).

The one place I see this effect behavior, if for email clients accessing 
IMAP - I've been seeing timeouts, and exceptionally high delays to load 
an inbox, or move stuff to the trash.

This pattern is new - and there's really nothing that I've changed in 
terms of configuration or loading that I can see.

So... any thoughts?  Any diagnostic approaches?

Thanks much,

Miles Fidelman

-- 
In theory, there is no difference between theory and practice.
In practice, there is.  .... Yogi Berra

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From: Curt <[email-masked]>
Date: Wed, 14 Sep 2016 08:00:29 +0000 (UTC)

> CPU is mostly in wait mode, and iotop shows low disk i/o traffic.

I'm looking here (maybe a little outdated from 2010?):

https://www.tummy.com/articles/isolating-heavy-load/

Maybe an idea or two.

-- 
“Whatever is rejected from the self, appears in the world as an event.” 
C.G. Jung

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From: Frédéric Marchal <[email-masked]>
Date: Wed, 14 Sep 2016 08:53:31 +0200

> CPU is mostly in wait mode, and iotop shows low disk i/o traffic.

How do you know the load is high? Where is the indication coming from?

> So... any thoughts?  Any diagnostic approaches?

Could the heat sink or fans be clogged with dust?

If heat can't be extracted properly, the CPU will lower its frequency and 
appears sluggish. The fan will turn at top speed too.

I'm interested in more opinions and diagnostic tools too because my laptop 
suddenly became very slow and unresponsive yesterday until I restarted it. top 
was showing a mostly idle cpu but kde system activity was displaying a lot of 
"disk sleep".

The computer was fast again if I stopped firefox and libreoffice calc. It went 
slow again if I started any of them. Restarting the computer solved the 
problem.

Frederic

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From: Miles Fidelman <[email-masked]>
Date: Wed, 14 Sep 2016 10:14:42 -0400

Well, I found out where all that load was coming from.

Looks like a recent Thunderbird update reset its config to "keep all 
messages for this account on this computer" - for all accounts

Given that I'm the admin for some servers, and a bunch of email lists, I 
keep filtered spam and viruses for analysis, and I keep email going back 
about 30 years....  that kind of causes a lot of synchronization traffic 
- to the point of really bogging down our imap daemon.

Consider this a friendly warning for those of you who use Thunderbird & 
IMAP!

Cheers,

Miles Fidelman

> Lately, our server has been showing high loading, but top shows that 
> the CPU is mostly in wait mode, and iotop shows low disk i/o traffic.
>
> The one place I see this effect behavior, if for email clients 
> accessing IMAP - I've been seeing timeouts, and exceptionally high 
> delays to load an inbox, or move stuff to the trash.
>

---

From: Tanstaafl <[email-masked]>
Date: Wed, 14 Sep 2016 10:41:21 -0400

> messages for this account on this computer" - for all accounts

The first time this fiasco happened - the update happened that enabled
GLODA for all accounts and reset all individual offline folder settings
for all accounts - was sometime around the TB 3 - 3.1 update. This was
the one time I seriously looked for an alternative to TB, it made me so
furious, as I have many (15+) IMAP accounts, most with a LOT of email
AND a lot of folders, and with very specific OFFLINE settings for
certain folders.

If the devs cause this to happen again, I will be even more furious than
I was then, even if it is an accident.

So, hopefully you are wrong, or it is some obscure bug (maybe triggered
by a misbehaved Addon) that will not hit me (or most users).