Friday, September 12, 2008

How to make a file read in Windows not become a write

A little known, and even less used, feature of all Windows versions from XP and forward is that they support a property called 'Last Access' on all files. On the surface, this seems neat, if not so useful. You can see whenever a file was last accessed using this property.

But think about it. What does this mean? It means that every time you open a file for reading, Windows needs to write something somewhere on the disk! If you're in the process of enumerating, lets say 500 000 files, this is equal to slow! Does anyone ever use that property? Not that I know of.

I'm working with file based persistent storage in my solutions, not with a database, so file access is pretty important to me. By disabling this 'feature', I speeded up enumerating the file system by about a factor of 10! Generally speaking, you'll speed up any system with many file accesses by turning this feature off.

It's really simple too. At a DOS-prompt write:

fsutil behavior set disablelastaccess 1 

When you're at it, you might also want to do:

fsutil behavior set disable8dot3 1 

This last command disables generation of 8-dot-3 legacy file names, effectively halfing the size of directories in NTFS, which must be a good thing. Beware that there might be 16-bit software out there which actually need those 8-dot-3 names to find your files...

No comments:

Post a Comment