From: vasudevram <vasudevram@...>
Date: 2006-07-27T00:20:06+09:00
Subject: Re: For performance, write it in C

> > On Wed, 26 Jul 2006 17:47:13 +0900, Peter Hickman wrote:
> > > In this post I want to clear some things up and provide benchmarks as to
> > > why you should take "Write it in C" seriously.

Interesting series of messages! Got to save and read them through at
leisure ...

Just adding my 2c:

[I worked on a fairly complex performance tuning job once, involving
HP-UNIX boxes (multiple),
Informix ESQL/C batch programs, IBM MQ series (now called Websphere
MQ), UNIX IPC, and got a chance to do tuning at several different
levels - SQL queries, MQ logs/partitions, the C code, algorithms in it,
etc. Was very educational ... just sharing some insights gained from
that, from reading on the subject, and from smaller hobby projects
tuning my own code ...]

[Not implying that previous posters on this thread haven't done any of
the below].

Performance tuning in general is *very* complicated. Guesses or
assumptions like "this code tweak should make it run faster" often do
not work. The only way is a (semi)scientific approach to
measure/profile, study profile results, make hypotheses, change code
accordingly, then re-measure to see if the change made a difference.

Tuning can be done at any of several different levels, ranging from:

- hardware (even here, not just throwing more boxes or faster boxes at
the problem, but things like hardware architecture - obviously only if
the skills are available and the problem is worth the effort)

- software architecture

- algorithms and data structures optimization

- plain code tuning (things like common subexpression elimination, e.g.
using C syntax, changing:

for (i = 0; i < getLength(my_collection); i++) { /* do something with
my_collection[i] */ }

to

collLength = getLength(my_collection);
for (i = 0; i < collLength; i++)  { /* do something with
my_collection[i] */ }

/* which removes the repeated/redundant call to the function
getLength() */

Jon Bentley's book "Writing Efficient Programs" is a very good book
which discusses rules, examples and war stories of tuning at almost all
of these levels, including really excellent advice on code-level
tuning, which may sometimes be the easiest one to implement on existing
code.
Though the examples are in a pseudo-Pascal dialect (easily
understandable for those knowing C), and though it may be out of print
now, for those who have a real need for tuning advice, its worth trying
to get a used copy on eBay, from a friend, whatever.

Its chock-full of code examples with the tuning results (verifiied by
measurement, as stated above), when (and when not) to apply them, and
the war stories are really interesting too ...

Googling for "performance tuning" and variants thereof will help ...

There's another book (for Java, mostly server-side programming) by a
guy called Dov (something - forget his last name and the book title, if
I remember it, will post here) that's *really* excellent too - he shows
(again, with actual measurements) how some of the "expected" results
were actually wrong/counter-intuitive. He worked with IBM on the web
software for one of the recent Olympics.

HTH
Vasudev
----------------------------------------------------------------------------------
Vasudev Ram
Custom utility development in UNIX/C/sh/Java/Python/Ruby
Software consulting and training
http://www.dancingbison.com
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