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Is strip-nondeterminism causing performance regressions in your packages?




Hi -devel,

In #877418 we discovered that strip-nondeterminism was degrading the
performance of clojure applications.

This turned out it was because strip-nondeterminism was normalising the
timestamps of both the source and compiled files (in this case, .clj and
.class files respectfully) to the same time. 

Clojure was then, at runtime, inferring that the .class files were out-of-
date with respect to the .clj's, resulting in a costly recompilation.

At the time of writing, the fix for #877418 has yet to be decided — and
please keep such discussions there! — I am writing this to -devel now in
case there are any other languages in Debian that may be suffering a
parallel problem.

Any which we do not ship compiled files cannot be affected (eg. we do not
ship Python's .pyc files; they are generated at installation-time), we
should just have a think about what other package sets:

 a) Ship both compiled & source in the .deb

and

 b) Do a *runtime* timestamp comparison between the two.


(Curiously, this is not the first time Reproducible Builds have caused
unintended side-effects; see, for example:)

  http://lists.alioth.debian.org/pipermail/reproducible-builds/Week-of-Mon-20170508/008717.html


Regards,

-- 
      ,''`.
     : :'  :     Chris Lamb
     `. `'`      lamby@xxxxxxxxxx / chris-lamb.co.uk
       `-