Shell Scripts v. Command Options (was: Re: small bug in who(1) of SVR3)

[John F Haugh II]

In article <1991Jan14.202053.20054 at zoo.toronto.edu> henry at zoo.toronto.edu (Henry Spencer) writes:
>Add up the costs of writing the C code, the costs of maintaining it, the
>costs of enhancing it to add the next round of silly "features", and so
>forth.  Now consider how many times per second "who" gets run, and how
>critical its performance is -- i.e., not very many and not very.  The
>optimization is not worth the price.

Studies have shown that the cost of maintaining code is largely independent
of the language and depends primarily on the amount of code.  A three line
change to a C file should be just as easy to maintain as a three line shell
script.

As for performance, benchmarks will indicate the fork() is an extremely
expensive system call.  When I was a Pinnacle Systems, one of my jobs was
to perform benchmarks on competitors equipment.  The average system that
I evaluated fork()'d less than 100 times per second, with many well below
30 or 40.  A certain 3 letter company's product fork'd about 20 times
per second.

Script is typescript, started Tue Jan 15 08:28:02 1991
rpp386-> cat fork.c
main ()
{
	int	i;

	for (i = 0;i  1000;i++)
		if (fork ())
			while (wait (0) != -1) ;
		else
			exit (0);
}
rpp386-> cc -o fork fork.c -O -s
fork.c
rpp386-> timex ./fork
execution complete, exit code = 1

real	        14.53
user	         0.83
sys	        12.72
rpp386-> calc 1000 / 14.53
	 68.82312456985548
rpp386-> exit
Script done Tue Jan 15 08:28:53 1991

>>... fork() and exec() are neither free nor even cheap - shell
>>scripts are just not the right answer.
>
>Odd; we've found that shell scripts are the right answer for an enormous
>range of applications.  "ls" is a shell script on utzoo (it invokes the
>Sun ls with the -1 option).  The question is not whether fork() and exec()
>are free -- obviously not -- or cheap -- thanks to manufacturer stupidity
>and greed, often they aren't -- but whether they are cheap *enough*.  The
>answer is usually "yes".

If you have more than 68 users on your system and it only forks 68 times
per second, you are likely to find that shell scripts run pretty damned
slow.  The command

who | cut -d' ' -f1 | sort | pr -6 -l1

will stop being fast *enough* the first time some collection of people
start kicking off the other shell scripts the have replaced the other
commands on the system.
-- 
John F. Haugh II                             UUCP: ...!cs.utexas.edu!rpp386!jfh
Ma Bell: (512) 832-8832                           Domain: jfh at rpp386.cactus.org
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