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

[Joachim Durchholz]

Hi all,

I'm having some trouble with a PmWiki installation that may, in fact, be 
more related to Apache/Linux configuration issues, but I haven't been 
able to exactly pin the problem down so my main question is whether 
anybody else has seen similar behavior.

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.)

I have done some server twiddling, reducing the number of processes that 
Apache preforks (it used to prefork an unreasonable number of processes, 
only to have them swapped out to disk - which is *not* what preforking 
is about *gg*). Either that or a decrease in server load has returned 
PmWiki to normal, sane behavior.


Here are my questions related to this issue:

1) Has anybody seen similar behavior?
2) Does anybody have a clue why PmWiki hangs, instead of returning an 
error message or simply abruptly terminating the connection? Or is it 
normal that the browser continues to wait for data when a PHP process 
was killed due to CPU/memory over-use?
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 :-)

Regards,
Jo