Issue #3924 has been updated by Xavier Shay.


Progress update:

Didn't get much time to work on this today, but came up with a benchmark to measure performance with a full $LOAD_PATH (suspected issue with slow rails loading), which indeed shows mine to have the same performance curve as 1.9.3, but with a higher multiplier:
https://gist.github.com/985224 (graph in the comments)

Doubling the number of available extensions (.bogus, .bogus2, etc...) doubled the multiplier, suggesting improvement in rb_locate_file_with_extensions could be a win.
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Bug #3924: Performance bug (in require?)
http://redmine.ruby-lang.org/issues/3924

Author: Carsten Bormann
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 1.9.3
ruby -v: ruby 1.9.2p0 (2010-08-18 revision 29036) [x86_64-darwin10] 


=begin
 Running irb < /dev/null in 1.9.2 causes 3016 calls to lstat64.
 
 For instance, there is a sequence of 28 repetitions each of lstat calls to all 6 non-empty path prefixes of /opt/local/lib/ruby1.9/1.9.1/irb.rb -- a total of 170 lstats apparently just to load this file; another set of lstats then occurs later for another 18 (times 6) times.  Clearly, something is running amok in the calling sequence rb_require_safe -> realpath_rec -> lstat.
 
 Another example: Running a simple test with the baretest gem causes 17008 calls to lstat.  According to perftools.rb, 80 % of the 1.2 seconds of CPU is used in Kernel#gem_original_require (and another 12 in GC, some of which may be caused by this).
=end



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