I just found another interesting observation. That regex I was using matches 125,277 times (16.3% of the lines) in the example file I was using. If I change the regex to /^ ?QueryXXX/; so that it matches nothing I get: 
0.114286 read lines from disk and do RE; n=769114.
0.104568 read lines from in-memory file and do RE; n=769114.

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This is probably more for the perl developers or cygwin distribution people, but still pretty quirky.

In reply to Re^2: RE on lines read from in-memory scalar is very slow by Danny
in thread RE on lines read from in-memory scalar is very slow by Danny

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