[tex-k] Speed of kpsewhich when querying the repertories of the TeX installation

[Reinhard Kotucha]

On 2015-05-01 at 16:10:17 +0900, Norbert Preining wrote:

 > > There must be at least one initial hard-coded path no? I can't
 > > relocate kpsewhich anywhere on my system or can I ?
 > 
 > You can relocate, check the installation of TeX Live, you can
 > choose whereever you want.
 > 
 > kpsewhich searches for the initial texmf.cnf in a (long) list
 > of defined locations, that allows for relocation, plus some
 > fixed locations.
 > 
 > > Are you sure kpsewhich does not do, apart from evaluating the
 > > contents of the texmf.cnf files, do some un-needed parsing of ls-R
 > 
 > Of course it does ls-R parsing, but it is not unneeded. Because 
 > the ls-R is used to find the other files, including other texmf.cnf
 > files (as far as I know).

Kpathsea needs the ls-R files in order to find all the *other* files
but it has to read the texmf.cnf file[s] *first* in order to know
where the ls-R files are i.e., which directory trees are defined in
the config file[s].

  kpsewhich --debug=-1 --expand-path=\$TEXMFHOME 2>&1 | grep 'Search path'
  kdebug:Search path for cnf files (from compile-time paths.h)
  kdebug:Search path for ls-R files (from texmf.cnf)

It seems that kpsewhich first evaluates 2015/texmf.cnf and then looks
for web2c directories in a list of pre-definened paths.

Finally it loads ls-R files but it doesn't search for any other web2c
directories in additional local trees.  Hence I think that the ls-R
files are not needed for variable expansion and evaluation may be
omitted for some particular kpsewhich options.

This is at least what I deduce from the output of 

  kpsewhich --debug=-1 --expand-path

but I fear that only Karl knows the whole story.

After all, I'm convinced that reading ls-R files is the most expensive
part here because the file system is involved.  If only variables have
to be expanded everything should be doable within a few milliseconds,
including the creation of the kpsewhich process itself.

Regards,
  Reinhard

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Reinhard Kotucha                            Phone: +49-511-3373112
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