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Slow stat() on noacl mounts due to x permission check
- From: Christian Franke <Christian dot Franke at t-online dot de>
- To: cygwin at cygwin dot com
- Date: Fri, 03 Feb 2012 19:20:57 +0100
- Subject: Slow stat() on noacl mounts due to x permission check
Cygwin stat() may be much slower on noacl mounts than on acl mounts.This
is because on noacl mounts the x-permission bit is guessed by checking
for "#!", ":" or "MZ" in the first bytes of the file. AFAIKS this is
done for all files except *.exe, *.lnk and *.com.
A real world testcase with 20120201 snapshot on a (C++/Java development)
tree with ~52000 files in ~12000 dirs:
. noacl acl
find -size ... (after boot) 518s 51s
find -size ... (disk cached) 13s 8s
find -name ... (disk cached) 3s 3s (does not need stat())
Is it really needed to do the header check for each file?
Would it break important use cases if the check is only done for files
with typical script file extensions?
For example: no extension, .sh, .csh, .pl, .py, ...
Another more flexible solution would be a mount option to configure this.
(xguess=0: no check; 1: some extensions only; 2: all files)
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