[pmwiki-users] PmWiki seems to "hang" on overloaded boxes

[Joachim Durchholz]

Radu wrote:

> At 08:11 AM 5/22/2005, Joachim Durchholz wrote:
> 
>> Here's what happened: PmWiki suddenly started to "hang", i.e. it
>> would not respond at all, or display only part of the output and
>> "hang". With "hang", I mean that the browser still has the
>> data-is-forthcoming animation, but no new data ever arrives. (For
>> an "forever" value of one or two minutes.)
> 
> Um. Have you tried deleting the .flock file? If after the one or two
>  minutes you actually do get the page, this is not the issue.

Well, once PmWiki hanged, calling up the site in another browser window
would stall as well, and deleting .flock would fix that.

>> 1) Has anybody seen similar behavior?
> 
> Similar, yes, but not being able to modify server setup, I've no idea
> if it's the same problem. Does it happen when you have a vanilla
> pmwiki or is it caused by some mods?

There are some mods installed, and indeed that was my first conjecture.
However, tweaking the Apache config has eliminated the problem, so I'm
tracing this to some overload condition.

To make it a bit clearer: I don't mind if PmWiki fails under overload -
it has every right to do so. What I don't like is its failure mode: no
error message, but a browser that keeps waiting for data that never
comes, and a dysfunctional site (.flock-induced, though I don't know
whether that's because the stalled PmWiki call never got around to
cleaning out .flock or due to some other reason).

>> 3) Does anybody know how to diagnose server load well? (I have a 
>> Debian Linux.) I need to see what processes go to swap, how much of
>>  each process got swapped out, CPU usage, and similar data. "top"
>> seems to fit the bill, but I find it difficult to interpret the
>> data (this may just be a case of RTFM, but I'd like to hear whether
>> there are friendlier alternatives before delving too deeply into
>> the "top" manual page - it's over 1000 lines...) "top" also seems
>> to be limited to giving a current-situation snapshot, no overview
>> over time - and I'd like to do a post-hoc analysis of how loaded
>> the system was at, say, three o'clock in the morning when I'm in
>> bed :-)
> 
> I would suggest debugging a top command very well, until it does
> exactly what you need, then place it on the crontab with a pipe into
> a log file.

Um... well... I wanted to avoid having to read all those man pages ;-)

Regards,
Jo