[pmwiki-users] pmwiki.org slow again

[Patrick R. Michaud]

On Wed, Apr 20, 2005 at 10:10:15PM +0200, Joachim Durchholz wrote:
> Just a short note to Pm: pmwiki.org just started to show latencies 
> again. I did a few measurements with a wall clock and got latencies 
> between 4 seconds (not very good but tolerable) and 85 seconds 
> (absolutely horrible).

Earlier today I got hit by a couple of nasty spiders that really
loaded down the server -- in fact, I ended up blocking the spiders'
IP addresses entirely.

> Once pmwiki.org begins to deliver, the page is completed within 
> fractions of a second, so it seems that the process is held up and 
> queued until the server gets around to serving the request.

This can be it, but PmWiki also does most of the formatting before
it delivers any portion of the page, so it could still be a formatting
issue.  The load levels on my site have been high all day due to heavy
traffic -- and a lot of it is non-wiki traffic so it's not just slowness
in PmWiki.

> I don't think it's a stuck harddrive, since then I'd expect pauses 
> between, say, serving the sidebar and the main contents (these are 
> separate file accesses).  

Actually, the sidebar is usually read and rendered after the main 
contents-- otherwise things like (:noleft:) can't work.

> That the latencies occur only at request start 
> points towards a simpler problem: server overload. 

It is server overload, but the server overload seems to be coming from
stuck disk accesses.  (The disk in this case is a shared network/virtual
drive, so the delay is not necessarily mechanical.) The webserver or PmWiki
will ask to read a file and the whole systems pauses waiting for the 
file to be retrieved.  I can actually see this from the command line
or while I'm editing, as a simple command such as "ls" hangs for 5-6
seconds before giving output.  And in that short hang time, several
more requests come into the webserver, spiking further the load for
limited CPU resources.

Pm