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authorShawn O. Pearce <spearce@spearce.org>2006-12-14 11:15:57 (GMT)
committerJunio C Hamano <junkio@cox.net>2006-12-16 06:11:19 (GMT)
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Avoid accessing a slow working copy during diffcore operations.
The Cygwin folks have done a fine job at creating a POSIX layer on Windows That Just Works(tm). However it comes with a penalty; accessing files in the working tree by way of stat/open/mmap can be slower for diffcore than inflating the data from a blob which is stored in a packfile. This performance problem is especially an issue in merge-recursive when dealing with nearly 7000 added files, as we are loading each file's content from the working directory to perform rename detection. I have literally seen (and sadly watched) paint dry in less time than it takes for merge-recursive to finish such a merge. On the other hand this very same merge runs very fast on Solaris. If Git is compiled with NO_FAST_WORKING_DIRECTORY set then we will avoid looking at the working directory when the blob in question is available within a packfile and the caller doesn't need the data unpacked into a temporary file. We don't use loose objects as they have the same open/mmap/close costs as the working directory file access, but have the additional CPU overhead of needing to inflate the content before use. So it is still faster to use the working tree file over the loose object. If the caller needs the file data unpacked into a temporary file its likely because they are going to call an external diff program, passing the file as a parameter. In this case reusing the working tree file will be faster as we don't need to inflate the data and write it out to a temporary file. The NO_FAST_WORKING_DIRECTORY feature is enabled by default on Cygwin, as that is the platform which currently appears to benefit the most from this option. Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
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