[ic] Iterations slow with mv_matchlimit incrementations

[Mike Heins]

Quoting Stefan Hornburg (Racke) (racke at linuxia.de):
> Gert van der Spoel wrote:
> >> -----Original Message-----
> >> From: interchange-users-bounces at icdevgroup.org [mailto:interchange-
> >> users-bounces at icdevgroup.org] On Behalf Of Grant
> >> Sent: Tuesday, May 12, 2009 9:16 AM
> >> To: interchange-users at icdevgroup.org
> >> Subject: Re: [ic] Iterations slow with mv_matchlimit incrementations
> >>
> >>>>> I have a somewhat complex chunk of IC code about 500 lines long.
> >>>>> If I
> >>>>> set the mv_matchlimit of the main loop to a small number, each
> >>>>> iteration takes less than a second to execute.  However, as I
> >>>>> increase
> >>>>> the mv_matchlimit, each iteration takes longer to execute until
> >> it's
> >>>>> quite slow.  I've been over my code again and again but I can't
> >>>>> find a
> >>>>> cause for this behavior.  The only clue I have is that each
> >> iteration
> >>>>> executes much faster when the loop is almost done with all of its
> >>>>> iterations.
> >>>>>
> >>>>> I'm wondering if the problem is "under the hood" of IC.  Does this
> >>>>> scenario ring a bell for anyone?
> >>>>>
> >>>>> Thanks,
> >>>>> Grant
> >>>> I'm baffled by this.  I have no idea why increasing mv_matchlimit
> >>>> would drastically increase the amount of time required for *each*
> >> loop
> >>>> iteration.  Please let me know if you have any ideas.
> >>> Is there any way you can post the relevant piece of code?  Without
> >>> knowing what's being iterated over, it's hard to offer suggestions.
> >>> In particular, are there any parts which are perl blocks of any
> >>> particular flavor (calc, calcn, perl, prefix-exec, etc)?  Are there
> >>> perhaps multiple nested loop constructs?
> >>>
> >>> Regards,
> >>>
> >>> David
> >> Here's another illustration of my problem.  I set up 15 [email] tags
> >> throughout my code so I get an email whenever certain points are
> >> reached.  With ml=10 I get maybe 20 or so emails per second.  With
> >> ml=999999 I get much less than 1 email per second.  My understanding
> >> is that the first 10 iterations should take the same amount of time in
> >> either scenario.
> >>
> >> Does anyone know why IC would execute a single iteration at a
> >> drastically slower rate, just because it has more total iterations to
> >> execute?
> >>
> >> My installation is a year or two old.  Does this sound like a problem
> >> an upgrade could fix?
> > 
> > e-mail does not seem to be the most useful medium to do performance tests.
> > Servers can start holding e-mails or other external influences can cause
> > e-mails to arrive less frequently.
> > 
> > Why not have 15 timestamps written to a logfile, so you can look at this
> > data and see if you can find any trends. Is it that the 15 timestamps are
> > increasing in interval equally?
> > So it was with 
> > ml=10:   time,  time+I,   time+I+I,  time+I+I+I    (10, 15, 20, 25 etc)
> > ml=999999:   time,   time+(Ix10),  time+(Ix10+Ix10),  time+(Ix10+Ix10+Ix10)
> > (10, 60, 110, 160 etc)
> > 
> > or does ml=999999  show a less regular pattern where it has a spike between
> > two timings?
> > 
> > But you can imagine that it is shooting in a black hole here without
> > actually seeing the code.
> 
> I agree :-). A possible explanation would be that the memory consumption on
> larger mv_matchlimit values slows things down (due to problems in the
> unknown code?).
> 

Two words: 

  string copying

-- 
Mike Heins
Perusion -- Expert Interchange Consulting    http://www.perusion.com/
phone +1.765.328.4479  <mike at perusion.com>

In character, in manners, in style, in all things, the supreme excellence
is simplicity. -- Longfellow