[ic] Iterations slow with mv_matchlimit incrementations

Stefan Hornburg racke at linuxia.de
Tue May 12 07:20:26 UTC 2009

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?).


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