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Re: Severe performance problem and proposed solution

From: Zack Weinberg
Subject: Re: Severe performance problem and proposed solution
Date: Tue, 26 Feb 2002 17:21:14 -0800
User-agent: Mutt/1.3.27i

On Tue, Feb 26, 2002 at 04:56:10PM -0800, Paul Eggert wrote:
> > From: Zack Weinberg <address@hidden>
> > Date: Tue, 26 Feb 2002 08:37:08 -0800
> > 
> > According to David Edelsohn <address@hidden>, AIX's /bin/sh and
> > /bin/ksh support $LINENO but have the same performance problem with
> > here documents.  That means the _test_ as implemented is not good
> > enough.  It may be possible to detect the problem and add a check for
> > it to the probe logic
> I thought about it a bit, but I don't see how to do this portably,
> using just shell commands.

In this case, we know that the problem is due to the creation of
thousands of temporary files which each subshell invocation creates
hard links to.  If, I say if, someone can generate a small script
that causes the shell to do this, then it could look into /tmp for the
scratch files.

> Can you assume that the people with the performance problems have
> access to a better shell like Bash?  If so, you can ask them to put
> CONFIG_SHELL=/path/to/bash before running configure.  That should
> solve the problem.

That is the currently recommended workaround; however, we would prefer
an automatic solution.

> For example, you might try using 'case' rather than 'if'.  Sometimes
> that avoids weird performance bugs in /bin/sh.  E.g. instead of:

Oh really?  That might indeed be worth trying, thanks.


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